Hello All Edd, Norm,
There is a selenium rectifier that is used to supply a voltage to the pre-amp to power up the filament in one of the 12AX7s and the light bulb. Which diode and resistor would you choose to replace it. Will the usual 1N4007 (1N4005, 1N4006, whatever) and 100 ohm current limiting resistor work here? It seems to me that it would.
I like that massive speaker transformer and the use of a filter choke. The pre-amp is another one will a lot of Phono equalizations.

Dave

Don't remember if that was a tandem SR unit , for the DC filament supply , providing FW vs 1/2 w, but the appropriate 1N4xxx diode(s) used on that units ~60 source should work fine, with its appropriately selected companion pwr dropping resistor for compensation when replacing of an original SR unit.

That should keep that pre amps front end as quiet as a meece urinating on cotton.

73's de Edd

Edd,
It's a 12AX7 Filament and a #47 lamp. The lamp has a 100 ohm resistor across it. The schematic is provided with each component. It's on a label attached to the chassis. The sams shows only one of the 12AX7 filaments, the label shows both filaments in series with the lamp. So it may be 18 - 20 volts. Th filter capacitor is 500mf @ 50 volts. The selenium rectifier has fewer rectifier sections that in a table radio but the squares are a little larger. In other words, there's less squares but they have larger (X, Y) dimensions. The Z dimension is smaller (shorter).
In another area of the schematic, the SAMS was wrong on a capacitor value. Some of the capacitors that actually said 103 (Brown, Black, Orange) .01 on them were valued at .001 (102) in the SAMs.

Thanks,

Dave
:Don't remember if that was a tandem SR unit , for the DC filament supply , providing FW vs 1/2 w, but the appropriate 1N4xxx diode(s) used on that units ~60 source should work fine, with its appropriately selected companion pwr dropping resistor for compensation when replacing of an original SR unit.
:
:That should keep that pre amps front end as quiet as a meece urinating on cotton.
:
:73's de Edd

Edd,
It's a 12AX7 Filament and a #47 lamp. The lamp has a 100 ohm resistor across it. The schematic is provided with each component. It's on a label attached to the chassis. The sams shows only one of the 12AX7 filaments, the label shows both filaments in series with the lamp.

THE 12AX7 IN SERIES OPERATION WITH THE LAMP WOULD REQUIRE ~18v AT 150 MA...IF THAT LAMP IS A PILOT LIGHT FUNCTION, THEY MIGHT BE TRYING TO COAX A LITTLE MORE LAMP RELIABILITY WITH THEIR SLIGHT SHUNTING TECHNIQUE TO DERATE IT.... BUT BOBBLE UP THE FIL SUPPLY A BIT..UNLESS IT WAS A BIT HIGH ALREADY ?

So it may be 18 - 20 volts. Th filter capacitor is 500mf @ 50 volts.

THATS SOMEWHAT CONSERVATIVE FILTERING..UNLESS THAT SR IS A TANDEM UNIT ...(3 LEADS OUT)...

The selenium rectifier has fewer rectifier sections that in a table radio but the squares are a little larger. In other words, there's less squares but they have larger (X, Y) dimensions. The Z dimension is smaller (shorter).

THATS THE NATURE OF SR's..... MORE SURFACTAL AREA FOR MORE CURRENT CAPABILITY OR MORE SECTIONS FOR HIGHER PIV RATINGS
OR A COMBINATION OF THE TWO...TALKING ABOUT SURFACE AREA ...REMEMBER SEEING ANY OLD FIRST GENERATON CAR BATTERY CHARGERS ?

In another area of the schematic, the SAMS was wrong on a capacitor value. Some of the capacitors that actually said 103 (Brown, Black, Orange) .01 on them were valued at .001 (102) in the SAMs.

WHAT WERE THEIR FUNCTIONS, IN AN AUDIO CKT OR IN RF BYPASSING APPLICATIONS ? PLUS THE TYPES OF CAPS AS WELL AS YOUR POSSIBILITY OF MEASURING ANOTHER OEM UNIT...IF AN IDENTICAL BRAND / TYPE / TWIN WAS FOUND BEING USED IN ANOTHER AREA OF THE SET ?

:Edd,
: It's a 12AX7 Filament and a #47 lamp. The lamp has a 100 ohm resistor across it. The schematic is provided with each component. It's on a label attached to the chassis. The sams shows only one of the 12AX7 filaments, the label shows both filaments in series with the lamp. So it may be 18 - 20 volts. Th filter capacitor is 500mf @ 50 volts. The selenium rectifier has fewer rectifier sections that in a table radio but the squares are a little larger. In other words, there's less squares but they have larger (X, Y) dimensions. The Z dimension is smaller (shorter).
: In another area of the schematic, the SAMS was wrong on a capacitor value. Some of the capacitors that actually said 103 (Brown, Black, Orange) .01 on them were valued at .001 (102) in the SAMs.
:
:Thanks,
:
:Dave
::Don't remember if that was a tandem SR unit , for the DC filament supply , providing FW vs 1/2 w, but the appropriate 1N4xxx diode(s) used on that units ~60 source should work fine, with its appropriately selected companion pwr dropping resistor for compensation when replacing of an original SR unit.
::
::That should keep that pre amps front end as quiet as a meece urinating on cotton.
::
::73's de Edd

My Dynaco pre-amp. has DC to the 12AX7s. The amplifier has absolutely no hum. Good idea. It uses seleniums, too. ....And speaking of seleniums and car chargers, the 1954 (and possibly earlier) Chevrolet could have an optional alternator. The rectifier was separate from the alternator, and was copper oxide, though it looked like a selenium. Everything is put into perspective when you see the unit next to the air cleaner, where it's normally mounted (to the intake manifold), and it's almost half the size of the air cleaner! It's a miracle what pellets they use in modern alternators!

T.

Thomas,
I put a 100 ohm resistor in series with the new rectifier but it's not enough current to light the tubes or resistor is hogging most of the voltage accross it. I want to remover it but what do I replace it with? or is the power transformer limiting the current enough so I don't really have to worry about a dropping resistor?
This is the rectifier that supplies filament to two 12AX7s in the pre-amp. Both filaments are in series along with a #47 lamp. There is a resistor accross the lamp as well. I cannot see the filaments lit but the lamp is on dimly. So I need to remove that resistor.

Thanks,

Dave
:My Dynaco pre-amp. has DC to the 12AX7s. The amplifier has absolutely no hum. Good idea. It uses seleniums, too. ....And speaking of seleniums and car chargers, the 1954 (and possibly earlier) Chevrolet could have an optional alternator. The rectifier was separate from the alternator, and was copper oxide, though it looked like a selenium. Everything is put into perspective when you see the unit next to the air cleaner, where it's normally mounted (to the intake manifold), and it's almost half the size of the air cleaner! It's a miracle what pellets they use in modern alternators!
:
:T.

100 ohm resistor is for high voltage low current situations where a selenium is replaced with a silicon. For low voltage high current situations, what's used for filtering in the former will not work well in the latter. For instance, my portable radio uses a 2,000 ohm dropping resistor with 40 MFD condensers before, in the middle, and after the resistor for filtering the filament voltage. If the filaments were fed from a 6 volt transformer with rectifier, they'd need 1000 MFD or higher filter capacitors, and without the extra voltage to work with, filter resistors/chokes would have to be very small, if at all.

With your silicon diode, if you need resistance for filtering, keep it small. You are better off increasing capacitance if you need to remove hum. Increase capacitance first. If you still have hum, check filament voltage. Introduce enough resistance to bring filament voltage down to where it should be, and no more. That's all you can do. If you still have hum problems, add more capacitance. Modern capacitors are small, so you can add quite a bit. You should see the spark I get when I parallel 10 3000 MFD 50 WVDC condensers! I can weld metal! Still, they don't take up much space.

If you add more capacitance, be sure that your diode can handle the initial current.

T.

The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.

T.

Thomas,
That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
If the 100 is too high, I'll take it down to 50.

Thanks,

Dave
:The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:
:T.

Yeah, it helps to know what the transformer voltaqge is.

If nothing else, it's nice to have a high wattage 100 ohm potentiometer lying around. I have one, myself. If you obtain one, you will be able to experiment with stuff like this without knowing all of the variables.

T.

Dave,

The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.

Radiodoc

:Thomas,
: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
: If the 100 is too high, I'll take it down to 50.
:
:Thanks,
:
:Dave
::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::
::T.

Radiodoc,
I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?

Thanks,

:Dave,
:
:The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:
:Radiodoc
:
:
::Thomas,
:: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:: If the 100 is too high, I'll take it down to 50.
::
::Thanks,
::
::Dave
:::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::
:::T.

Dave,

What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.

Radiodoc
*******************

:Radiodoc,
: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:
:Thanks,
:
::Dave,
::
::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::
::Radiodoc
::
::
:::Thomas,
::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::: If the 100 is too high, I'll take it down to 50.
:::
:::Thanks,
:::
:::Dave
::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::
::::T.

Radiodoc,
Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.

Thanks,

:Dave,
:
:What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:
:Radiodoc
:*******************
:
:
::Radiodoc,
:: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::
::Thanks,
::
:::Dave,
:::
:::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::
:::Radiodoc
:::
:::
::::Thomas,
:::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::: If the 100 is too high, I'll take it down to 50.
::::
::::Thanks,
::::
::::Dave
:::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::
:::::T.

Dave,

That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.

Radiodoc

:Radiodoc,
: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:
:Thanks,
:
::Dave,
::
::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::
::Radiodoc
::*******************
::
::
:::Radiodoc,
::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::
:::Thanks,
:::
::::Dave,
::::
::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::
::::Radiodoc
::::
::::
:::::Thomas,
::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::: If the 100 is too high, I'll take it down to 50.
:::::
:::::Thanks,
:::::
:::::Dave
::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::
::::::T.

Radiodoc,
You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?

Thanks,

Dave
:Dave,
:
:That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:
:Radiodoc
:
:
::Radiodoc,
:: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::
::Thanks,
::
:::Dave,
:::
:::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::
:::Radiodoc
:::*******************
:::
:::
::::Radiodoc,
:::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::
::::Thanks,
::::
:::::Dave,
:::::
:::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::
:::::Radiodoc
:::::
:::::
::::::Thomas,
:::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::: If the 100 is too high, I'll take it down to 50.
::::::
::::::Thanks,
::::::
::::::Dave
:::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::
:::::::T.

Radidoc,
Part of this page seems to have the answer to my question:

http://www.triodeel.com/7591.htm

If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.

Thanks,

Dave
:Radiodoc,
: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
:
:Thanks,
:
:Dave
::Dave,
::
::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
::
::Radiodoc
::
::
:::Radiodoc,
::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:::
:::Thanks,
:::
::::Dave,
::::
::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::::
::::Radiodoc
::::*******************
::::
::::
:::::Radiodoc,
::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::::
:::::Thanks,
:::::
::::::Dave,
::::::
::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::::
::::::Radiodoc
::::::
::::::
:::::::Thomas,
::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::::: If the 100 is too high, I'll take it down to 50.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::::
::::::::T.

Dave,

The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.

Radiodoc
***********

:Radidoc,
: Part of this page seems to have the answer to my question:
:
:http://www.triodeel.com/7591.htm
:
:If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
:
:Thanks,
:
:Dave
::Radiodoc,
:: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
::
::Thanks,
::
::Dave
:::Dave,
:::
:::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:::
:::Radiodoc
:::
:::
::::Radiodoc,
:::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::::
::::Thanks,
::::
:::::Dave,
:::::
:::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::::
:::::Radiodoc
:::::*******************
:::::
:::::
::::::Radiodoc,
:::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::::
::::::Thanks,
::::::
:::::::Dave,
:::::::
:::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::::
:::::::Radiodoc
:::::::
:::::::
::::::::Thomas,
:::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::::: If the 100 is too high, I'll take it down to 50.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::::
:::::::::T.

Radiodoc,
I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?

Thanks,

:Dave,
:
:The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
:
:Radiodoc
:***********
:
::Radidoc,
:: Part of this page seems to have the answer to my question:
::
::http://www.triodeel.com/7591.htm
::
::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
::
::Thanks,
::
::Dave
:::Radiodoc,
::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
:::
:::Thanks,
:::
:::Dave
::::Dave,
::::
::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
::::
::::Radiodoc
::::
::::
:::::Radiodoc,
::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:::::
:::::Thanks,
:::::
::::::Dave,
::::::
::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::::::
::::::Radiodoc
::::::*******************
::::::
::::::
:::::::Radiodoc,
::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::::::
:::::::Thanks,
:::::::
::::::::Dave,
::::::::
::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::::::
::::::::Radiodoc
::::::::
::::::::
:::::::::Thomas,
::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::::::: If the 100 is too high, I'll take it down to 50.
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::::::
::::::::::T.

Dave,

That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.

Radiodoc
************

Radiodoc,
: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
:
:Thanks,
:
::Dave,
::
::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
::
::Radiodoc
::***********
::
:::Radidoc,
::: Part of this page seems to have the answer to my question:
:::
:::http://www.triodeel.com/7591.htm
:::
:::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
:::
:::Thanks,
:::
:::Dave
::::Radiodoc,
:::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
::::
::::Thanks,
::::
::::Dave
:::::Dave,
:::::
:::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:::::
:::::Radiodoc
:::::
:::::
::::::Radiodoc,
:::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::::::
::::::Thanks,
::::::
:::::::Dave,
:::::::
:::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::::::
:::::::Radiodoc
:::::::*******************
:::::::
:::::::
::::::::Radiodoc,
:::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::::::
::::::::Thanks,
::::::::
:::::::::Dave,
:::::::::
:::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::::::
:::::::::Radiodoc
:::::::::
:::::::::
::::::::::Thomas,
:::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::::::: If the 100 is too high, I'll take it down to 50.
::::::::::
::::::::::Thanks,
::::::::::
::::::::::Dave
:::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::::::
:::::::::::T.

Giles,
The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.

Thanks,

Dave
:Dave,
:
:That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
:
:Radiodoc
:************
:
:Radiodoc,
:: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
::
::Thanks,
::
:::Dave,
:::
:::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
:::
:::Radiodoc
:::***********
:::
::::Radidoc,
:::: Part of this page seems to have the answer to my question:
::::
::::http://www.triodeel.com/7591.htm
::::
::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
::::
::::Thanks,
::::
::::Dave
:::::Radiodoc,
::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
:::::
:::::Thanks,
:::::
:::::Dave
::::::Dave,
::::::
::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
::::::
::::::Radiodoc
::::::
::::::
:::::::Radiodoc,
::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:::::::
:::::::Thanks,
:::::::
::::::::Dave,
::::::::
::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::::::::
::::::::Radiodoc
::::::::*******************
::::::::
::::::::
:::::::::Radiodoc,
::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::::::::
:::::::::Thanks,
:::::::::
::::::::::Dave,
::::::::::
::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::::::::
::::::::::Radiodoc
::::::::::
::::::::::
:::::::::::Thomas,
::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::::::::: If the 100 is too high, I'll take it down to 50.
:::::::::::
:::::::::::Thanks,
:::::::::::
:::::::::::Dave
::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::::::::
::::::::::::T.

:Radiodoc,
: The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
: I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.
:
:Thanks,
:
:Dave
::Dave,
::
::That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
::
::Radiodoc
::************
::
::Radiodoc,
::: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
:::
:::Thanks,
:::
::::Dave,
::::
::::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
::::
::::Radiodoc
::::***********
::::
:::::Radidoc,
::::: Part of this page seems to have the answer to my question:
:::::
:::::http://www.triodeel.com/7591.htm
:::::
:::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
:::::
:::::Thanks,
:::::
:::::Dave
::::::Radiodoc,
:::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Dave,
:::::::
:::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:::::::
:::::::Radiodoc
:::::::
:::::::
::::::::Radiodoc,
:::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::::::::
::::::::Thanks,
::::::::
:::::::::Dave,
:::::::::
:::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::::::::
:::::::::Radiodoc
:::::::::*******************
:::::::::
:::::::::
::::::::::Radiodoc,
:::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::::::::
::::::::::Thanks,
::::::::::
:::::::::::Dave,
:::::::::::
:::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::::::::
:::::::::::Radiodoc
:::::::::::
:::::::::::
::::::::::::Thomas,
:::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::::::::: If the 100 is too high, I'll take it down to 50.
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
:::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::::::::
:::::::::::::T.

:Giles (oops, this is supposed to be to Radiodoc, I made a typo),
: The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
: I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.
:
:Thanks,
:
:Dave
::Dave,
::
::That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
::
::Radiodoc
::************
::
::Radiodoc,
::: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
:::
:::Thanks,
:::
::::Dave,
::::
::::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
::::
::::Radiodoc
::::***********
::::
:::::Radidoc,
::::: Part of this page seems to have the answer to my question:
:::::
:::::http://www.triodeel.com/7591.htm
:::::
:::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
:::::
:::::Thanks,
:::::
:::::Dave
::::::Radiodoc,
:::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Dave,
:::::::
:::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:::::::
:::::::Radiodoc
:::::::
:::::::
::::::::Radiodoc,
:::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::::::::
::::::::Thanks,
::::::::
:::::::::Dave,
:::::::::
:::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::::::::
:::::::::Radiodoc
:::::::::*******************
:::::::::
:::::::::
::::::::::Radiodoc,
:::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::::::::
::::::::::Thanks,
::::::::::
:::::::::::Dave,
:::::::::::
:::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::::::::
:::::::::::Radiodoc
:::::::::::
:::::::::::
::::::::::::Thomas,
:::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::::::::: If the 100 is too high, I'll take it down to 50.
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
:::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::::::::
:::::::::::::T.

Dave,

Install a 20 Ohm resistor and I think you have got it.

Radiodoc
************

::Giles (oops, this is supposed to be to Radiodoc, I made a typo),
:: The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
:: I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.
::
::Thanks,
::
::Dave
:::Dave,
:::
:::That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
:::
:::Radiodoc
:::************
:::
:::Radiodoc,
:::: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
::::
::::Thanks,
::::
:::::Dave,
:::::
:::::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
:::::
:::::Radiodoc
:::::***********
:::::
::::::Radidoc,
:::::: Part of this page seems to have the answer to my question:
::::::
::::::http://www.triodeel.com/7591.htm
::::::
::::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Radiodoc,
::::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Dave,
::::::::
::::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
::::::::
::::::::Radiodoc
::::::::
::::::::
:::::::::Radiodoc,
::::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
::::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:::::::::
:::::::::Thanks,
:::::::::
::::::::::Dave,
::::::::::
::::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::::::::::
::::::::::Radiodoc
::::::::::*******************
::::::::::
::::::::::
:::::::::::Radiodoc,
::::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::::::::::
:::::::::::Thanks,
:::::::::::
::::::::::::Dave,
::::::::::::
::::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::::::::::
::::::::::::Radiodoc
::::::::::::
::::::::::::
:::::::::::::Thomas,
::::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::::::::::: If the 100 is too high, I'll take it down to 50.
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
::::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::::::::::
::::::::::::::T.

Radiodoc,
Why can't I leave the adjustable resistor there? It seems to work ok.

Thanks,

Dave
:Dave,
:
:Install a 20 Ohm resistor and I think you have got it.
:
:Radiodoc
:************
:
:::Giles (oops, this is supposed to be to Radiodoc, I made a typo),
::: The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
::: I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.
:::
:::Thanks,
:::
:::Dave
::::Dave,
::::
::::That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
::::
::::Radiodoc
::::************
::::
::::Radiodoc,
::::: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
:::::
:::::Thanks,
:::::
::::::Dave,
::::::
::::::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
::::::
::::::Radiodoc
::::::***********
::::::
:::::::Radidoc,
::::::: Part of this page seems to have the answer to my question:
:::::::
:::::::http://www.triodeel.com/7591.htm
:::::::
:::::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Radiodoc,
:::::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::Dave,
:::::::::
:::::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
:::::::::
:::::::::Radiodoc
:::::::::
:::::::::
::::::::::Radiodoc,
:::::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
:::::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
::::::::::
::::::::::Thanks,
::::::::::
:::::::::::Dave,
:::::::::::
:::::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
:::::::::::
:::::::::::Radiodoc
:::::::::::*******************
:::::::::::
:::::::::::
::::::::::::Radiodoc,
:::::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
::::::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
:::::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
::::::::::::
::::::::::::Thanks,
::::::::::::
:::::::::::::Dave,
:::::::::::::
:::::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
:::::::::::::
:::::::::::::Radiodoc
:::::::::::::
:::::::::::::
::::::::::::::Thomas,
:::::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
:::::::::::::: If the 100 is too high, I'll take it down to 50.
::::::::::::::
::::::::::::::Thanks,
::::::::::::::
::::::::::::::Dave
:::::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
:::::::::::::::
:::::::::::::::T.

Dave,

You can and it should work just fine. Just thought you may need the adjustable resistor again some time.

Radiodoc
************

:Radiodoc,
: Why can't I leave the adjustable resistor there? It seems to work ok.
:
:Thanks,
:
:Dave
::Dave,
::
::Install a 20 Ohm resistor and I think you have got it.
::
::Radiodoc
::************
::
::::Giles (oops, this is supposed to be to Radiodoc, I made a typo),
:::: The two tubes are about a volt apart. So when one is 13 volts the other is 12 volts. I am pretty sure that the equivalent voltage to 12.6 volts AC (RMS) in DC is almost 18 volts. So what should I set the tube's DC filament voltage to?
:::: I'll check the tube data at Frank's Electron Tube pages. I hope everyone has heard of the site. No it says 12.6 volts +/- 1.3 volts is fine. I have that. One tube gets 13 and the other gets 12. I think that thats fine and it's about 20 ohms. It goes over 14 volts if I reduce the resistance much further.
::::
::::Thanks,
::::
::::Dave
:::::Dave,
:::::
:::::That is correct. Make sure the tube has its proper voltage. The lamp may have less across it since it has a 100 Ohm resistor across it.
:::::
:::::Radiodoc
:::::************
:::::
:::::Radiodoc,
:::::: I see, you mean make sure they are as close to each other as possible and not exceed about 12 volts. Is that correct?
::::::
::::::Thanks,
::::::
:::::::Dave,
:::::::
:::::::The tube specifications I mentioned are in a tube charasteristics book. What I meant was just measure across one of the tubes at 4 & 5 and set the voltage and then check the voltage on the other tube's 4 & 5.
:::::::
:::::::Radiodoc
:::::::***********
:::::::
::::::::Radidoc,
:::::::: Part of this page seems to have the answer to my question:
::::::::
::::::::http://www.triodeel.com/7591.htm
::::::::
::::::::If the filaments are in series it recommends a resistor value between 1/2 and 2 ohms. So even 25 ohms may be too high. I hope that my adjustable wire wound resistor can be set that low.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::Radiodoc,
::::::::: You mean the tube manufacturer's specs. There don't seem to be any on the schematic. I will measure a tube's filament voltage on pins 4 and 5. I wish I had two meters. I probably do. I will connect both meters when I adjust the voltage. I only have one control. So there's no way I can adjust both at the same time. But it will probably stabilize at 6 volts DC. Usually it's 6.3 volts AC. Wouldn't the DC voltage be a higher number?
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::Dave,
::::::::::
::::::::::That would probably work. I am not sure why the lamp has a 100 Ohm resistor across it unless it is to dampen surge from the rectifier. The tubes probably have a controlled warmup, pretty sure the lamp does not. However, personally I would measure the voltage on the 12AX7 tubes. The filament voltage needs to be close to the manufacturer's specification for proper operation.
::::::::::
::::::::::Radiodoc
::::::::::
::::::::::
:::::::::::Radiodoc,
::::::::::: Would it also work if I measure 6 volts on the lamp? That's easier to measure. Or must I measure pins 4 and 5 on the tubes.
::::::::::: I also have a power resistor with a tap that can be screwed down into place. That is also a rheostat that I can leave inside the amplifier, once the value is established. A very good idea.
:::::::::::
:::::::::::Thanks,
:::::::::::
::::::::::::Dave,
::::::::::::
::::::::::::What would be nice is if you had a 50 or 100 ohm reostat rated around a couple of watts. Install it making sure it was set to the highest resistance. Then gradually adjust it until you had 12 volts on pins 4 & 5 of the 12AX7s. Measure the resistance setting of the reostat and install that value of fixed resistor in its place.
::::::::::::
::::::::::::Radiodoc
::::::::::::*******************
::::::::::::
::::::::::::
:::::::::::::Radiodoc,
::::::::::::: I tried 50 ohms and now the dial light is dim and the tubes seem to work ok. Should I try 25 ohms or 10 ohms? I have no idea. I'm using a 1 amp 1N4xx type diode. OK here is a full discription of the circuit. The winding from the power transformer (unknown voltage, current), one end of the winding is connected to a rectifier diode. It's positive output is connected to a 470 mf 50 volt electrolytic capcitor. There is a 22K ohm resistor across the capacitor. This output is fed into an output pin from the amplifier/power supply unit. In the pre-amp, there is a filament string with the dial lamp in between. Everything is in series. There is a 100 ohm resistor across the dial lamp.
:::::::::::::The filament pins used on the tube are 4 and 5. The negative end of the filter capacitor is connected to the other end of the power transformer winding. This is a simple series circuit. Why is it so difficult to find a current limiting resistor?
::::::::::::: I think that right now each tube filament is seeing 2.5 volts, and amazingly, it works. Without knowing what that winding is capable of, there's no way to tell what the resistor should be. It's just trial and error, and error could be distroying expensive tube filaments. Is it ok to leave the tubes working on 1/2 filament voltage?
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
::::::::::::::Dave,
::::::::::::::
::::::::::::::The 12AX7 filament is rated 12.6 volts at 150MA if filament voltage is applied to pins 4 & 5 only. Pin 9 is the filament center. If pins 4 & 5 are connected together then the filament voltage will be 6.3 volts at 300 MA between 4/5 and 9.
::::::::::::::
::::::::::::::Radiodoc
::::::::::::::
::::::::::::::
:::::::::::::::Thomas,
::::::::::::::: That still doesn't tell me what resistor to use. I know that the 3 items are in series. each tube takes 6 volts (I know it's called a 12AX7 but it's probably 6 volts). The lamp is 6 volts. The tube filaments take 150 mA. So I assume that the current needs to be 150 mA. But we don't know the voltage of the winding in the power transformer.
::::::::::::::: If the 100 is too high, I'll take it down to 50.
:::::::::::::::
:::::::::::::::Thanks,
:::::::::::::::
:::::::::::::::Dave
::::::::::::::::The 100 ohm resistor trick for silicon in the B circuit is kind of a 'one size fits all' trick. When you're dealing with low voltages and high currents, precision requires you to stick more to the E=IR scheme. Resistance affects high current circuits more than it affects low current ones. You must be very accurate in high current circuits if you wish to have proper voltages. As a third example, the corrosion on the prongs of a plug that still allows the lamp to light at full brightness, might not let your car start properly, if at all.
::::::::::::::::
::::::::::::::::T.