Thanks, Steve
Even though your 35Y4 tests good it may have an open section of filament. Check between pins #1, 4 and 8 with an ohm meter. All should show continuity.
Some tube testers check one section of filament. The second section is across the lamp and prevents it from burning out on turn on.
Norm
http://www.nostalgiaair.org/PagesByModel/333/M0002333.pdf
:I have finished repairing an old Bendix model 300 and it works great except for one thing. It blows out the #47 pilot lights as soon as I turn the switch on. If I use the VARIAC and bring the line voltage up slowly, the lights get real bright but do not blow. I've there are no ballast resistors in this radio but the lights act like they are given a shot of very high voltage when the set is turned on (and line voltage is 115v). Could I have a loose connection causing arcing somewhere which would cause a current spike? Tubes all check out OK and voltages are in the green. I can't afford any more pilot lights nor can I keep the radio permanently plugged to my VARIAC. Any ideas??
:
:Thanks, Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
Steve
Good to hear you got the radio working. You should use a #47 lamp if you have a bayonet socket. Other lamps draw more current and will be dim.
If that resistor is in series with your 35Y4 plate you can't go by ohms law reading a meter. Voltage is dropped across this resistor for less than 50% of a cycle. During this 50% twice the current has to be drawn in order to supply voltage during the off time. This is hard to understand but voltage dropped across this resistor is more than twice what a meter reads for less than 50% of the time.
Sometimes resistors were used in series with filaments. They help prevent a turn on surge. If this resistor is in series with filaments it has to be greater than 1/2 watt. 47 ohms drops 7 volts @ .15 amps. 7 times .15 = More than 1 watt.
Norm
:Norm,
:
:I checked the 1,4&8 pins on the 35Y4 tube and they all show continuity. I did find a small power resistor that was open (47ohm 1/2 watt). Looks like it was in series with the tube filaments. I replaced it and now the pilot lights don't blow but they are very dim. Also, why should this "ballast" resistor be needed since all the tube voltages add up to over 115 volts? The new resister has the same rating as the old but acts like it has much more resistance than 47ohms. Appreciate the help.
:
:Steve
:
::Steve
::
Let's talk now as though you're using only one #47 bulb, and I'll describe what is done later with two bulbs. The 35W4 tube has the two part filament wired as such: pin 4 begins the filament through the small section; pin 6 taps the filament, ending the small section, and beginning the large 35 volt section used to actually light the tube. When the tube is wired so that a pilot lamp may be used on it, the line cord is connected to pin 4. Current flows through the small portion of the filament to pin 6, and then on to the large portion to the filament to pin 3, and then out pin 3 to all the other tubes in the series string. If you don't already get the picture, the large filament between 6 and 3 is what actually lights the tube. The filament between 6 and 4 only serves as a ballast for the pilot lamp and other purposes to be described. The pilot lamp is connected across pins 4 and 6, taking advantage of the voltage drop in this small portion of the filament. This voltage, alone, is not enough to drive the pilot lamp to full brightness, so what is also done is the connection to the rectifier plate is made at pin 6. You will notice this in that the pilot lamp will not burn at full brightness until the radio starts to operate. This serves a double purpose. It causes a higher current to flow through the pilot lamp and small portion of filament, and the pilot lamp and tube filament serve in return as a sort of safety fuse. If, for some reason the power supply overloads, these may be blown. Since this extra current is being drawn by hooking B+ to pin 6, it is also important that the pilot lamp be replaced immediately upon burn-out, as having B+ drawn on the filament along with the regular filament current will cause it to burn too brightly with a failed pilot lamp, and eventually this filament will fail as well. At any rate, your radio has two pilot lamps from what it sounds like you're writing. What you must do now to get them to glow at full brightness is to put something in series with the filament in the 35W4 that serves for these bulbs. A rough equivilant to this filament is a 1 watt 47 ohm resistor. As far as tube connections, there should be a 47 ohm resistor with one side connected to the line cord, and one side connected to pin 4 of the 35W4 tube. Now the pilot lamps, which are strung in series, are connected, one end to where the 47 ohm resistor meets the line cord, and the other end to pin 6. Also connected to pin 6 should be a lead either directly connected to or through an additional resistor of small value to the plate of the tube (pin 5). This connection proceedure should yield bulbs of normal brightness. What I have done in the past, though, was to substitute the 47 ohm resistor with a dud tube in which the filament is still good, and linger this tube under the chassis. Since you are using a tube filament, which changes in resistance as it heats, where-as a resistor does not do so as much, you will get truer results. You can either use a 12AV6 tube (pins 3 and 4), or a dud 35W4 tube using pins 4 and 6. The 35W4 gives better results. Connect wires to this tube, and connect these wires to where the resistor would have been. Then wrap the pin part of the tube with electrical tape. A good tape to use is old fashioned electricians' cloth "friction" tape, as it holds well, and won't shrink or come loose like rubber tape. It is available at most True Value stores, and many other hardware stores.
A word of caution is that you must connect your pilot lamps to the 35W4 tube exactly as stated above. These are the correct filament connections. If you connect the 35W4 tube in any other way, you will have poor results. If you connect the pilot lamps to say pins 6 and 3 or 3 and 4, you will have blown pilot lamps. I have seen quite a few basing diagrams in tube diagram books that label the pilot lamp tap on the wrong tube. Evidently they did not proof-read their work. The above way is the correct and only way to connect the pilot lamps.
Hope this helps.
Thomas
:I have finished repairing an old Bendix model 300 and it works great except for one thing. It blows out the #47 pilot lights as soon as I turn the switch on. If I use the VARIAC and bring the line voltage up slowly, the lights get real bright but do not blow. I've there are no ballast resistors in this radio but the lights act like they are given a shot of very high voltage when the set is turned on (and line voltage is 115v). Could I have a loose connection causing arcing somewhere which would cause a current spike? Tubes all check out OK and voltages are in the green. I can't afford any more pilot lights nor can I keep the radio permanently plugged to my VARIAC. Any ideas??
:
:Thanks, Steve
Thomas
:Hello. How many pilot lamps are on your radio?? It sounds like you have two. Of course, like Norm said, they must be #47 bulbs. Commonly, if a wrong type is put in, it'll be the 44, which draws more current, and won't burn brightly with the .15 ampere tubes. 44 is .3 amperes, and 47 is .15 amperes. The pilot lamp tap on your 35W4 tube is designed to run one 47 bulb at full brightness. If your radio has two lamps, they are likely strung in series, and will not burn at full brightness with the 6.3 volt .15 ampere output from the filament tap. This is where the 47 ohm resistor comes into play.
:
:Let's talk now as though you're using only one #47 bulb, and I'll describe what is done later with two bulbs. The 35W4 tube has the two part filament wired as such: pin 4 begins the filament through the small section; pin 6 taps the filament, ending the small section, and beginning the large 35 volt section used to actually light the tube. When the tube is wired so that a pilot lamp may be used on it, the line cord is connected to pin 4. Current flows through the small portion of the filament to pin 6, and then on to the large portion to the filament to pin 3, and then out pin 3 to all the other tubes in the series string. If you don't already get the picture, the large filament between 6 and 3 is what actually lights the tube. The filament between 6 and 4 only serves as a ballast for the pilot lamp and other purposes to be described. The pilot lamp is connected across pins 4 and 6, taking advantage of the voltage drop in this small portion of the filament. This voltage, alone, is not enough to drive the pilot lamp to full brightness, so what is also done is the connection to the rectifier plate is made at pin 6. You will notice this in that the pilot lamp will not burn at full brightness until the radio starts to operate. This serves a double purpose. It causes a higher current to flow through the pilot lamp and small portion of filament, and the pilot lamp and tube filament serve in return as a sort of safety fuse. If, for some reason the power supply overloads, these may be blown. Since this extra current is being drawn by hooking B+ to pin 6, it is also important that the pilot lamp be replaced immediately upon burn-out, as having B+ drawn on the filament along with the regular filament current will cause it to burn too brightly with a failed pilot lamp, and eventually this filament will fail as well. At any rate, your radio has two pilot lamps from what it sounds like you're writing. What you must do now to get them to glow at full brightness is to put something in series with the filament in the 35W4 that serves for these bulbs. A rough equivilant to this filament is a 1 watt 47 ohm resistor. As far as tube connections, there should be a 47 ohm resistor with one side connected to the line cord, and one side connected to pin 4 of the 35W4 tube. Now the pilot lamps, which are strung in series, are connected, one end to where the 47 ohm resistor meets the line cord, and the other end to pin 6. Also connected to pin 6 should be a lead either directly connected to or through an additional resistor of small value to the plate of the tube (pin 5). This connection proceedure should yield bulbs of normal brightness. What I have done in the past, though, was to substitute the 47 ohm resistor with a dud tube in which the filament is still good, and linger this tube under the chassis. Since you are using a tube filament, which changes in resistance as it heats, where-as a resistor does not do so as much, you will get truer results. You can either use a 12AV6 tube (pins 3 and 4), or a dud 35W4 tube using pins 4 and 6. The 35W4 gives better results. Connect wires to this tube, and connect these wires to where the resistor would have been. Then wrap the pin part of the tube with electrical tape. A good tape to use is old fashioned electricians' cloth "friction" tape, as it holds well, and won't shrink or come loose like rubber tape. It is available at most True Value stores, and many other hardware stores.
:
:A word of caution is that you must connect your pilot lamps to the 35W4 tube exactly as stated above. These are the correct filament connections. If you connect the 35W4 tube in any other way, you will have poor results. If you connect the pilot lamps to say pins 6 and 3 or 3 and 4, you will have blown pilot lamps. I have seen quite a few basing diagrams in tube diagram books that label the pilot lamp tap on the wrong tube. Evidently they did not proof-read their work. The above way is the correct and only way to connect the pilot lamps.
:
:Hope this helps.
:
:Thomas
::I have finished repairing an old Bendix model 300 and it works great except for one thing. It blows out the #47 pilot lights as soon as I turn the switch on. If I use the VARIAC and bring the line voltage up slowly, the lights get real bright but do not blow. I've there are no ballast resistors in this radio but the lights act like they are given a shot of very high voltage when the set is turned on (and line voltage is 115v). Could I have a loose connection causing arcing somewhere which would cause a current spike? Tubes all check out OK and voltages are in the green. I can't afford any more pilot lights nor can I keep the radio permanently plugged to my VARIAC. Any ideas??
::
::Thanks, Steve
Thomas
:Speaking of not proof reading, what I meant at the bottom where I was talking about tube diagram books not labeling the 35W4 tube correctly, I meant they had the pilot lamp tap labeled on the wrong >pin<, not the wrong tube. Sorry.
:
:Thomas
:
:
:
::Hello. How many pilot lamps are on your radio?? It sounds like you have two. Of course, like Norm said, they must be #47 bulbs. Commonly, if a wrong type is put in, it'll be the 44, which draws more current, and won't burn brightly with the .15 ampere tubes. 44 is .3 amperes, and 47 is .15 amperes. The pilot lamp tap on your 35W4 tube is designed to run one 47 bulb at full brightness. If your radio has two lamps, they are likely strung in series, and will not burn at full brightness with the 6.3 volt .15 ampere output from the filament tap. This is where the 47 ohm resistor comes into play.
::
::Let's talk now as though you're using only one #47 bulb, and I'll describe what is done later with two bulbs. The 35W4 tube has the two part filament wired as such: pin 4 begins the filament through the small section; pin 6 taps the filament, ending the small section, and beginning the large 35 volt section used to actually light the tube. When the tube is wired so that a pilot lamp may be used on it, the line cord is connected to pin 4. Current flows through the small portion of the filament to pin 6, and then on to the large portion to the filament to pin 3, and then out pin 3 to all the other tubes in the series string. If you don't already get the picture, the large filament between 6 and 3 is what actually lights the tube. The filament between 6 and 4 only serves as a ballast for the pilot lamp and other purposes to be described. The pilot lamp is connected across pins 4 and 6, taking advantage of the voltage drop in this small portion of the filament. This voltage, alone, is not enough to drive the pilot lamp to full brightness, so what is also done is the connection to the rectifier plate is made at pin 6. You will notice this in that the pilot lamp will not burn at full brightness until the radio starts to operate. This serves a double purpose. It causes a higher current to flow through the pilot lamp and small portion of filament, and the pilot lamp and tube filament serve in return as a sort of safety fuse. If, for some reason the power supply overloads, these may be blown. Since this extra current is being drawn by hooking B+ to pin 6, it is also important that the pilot lamp be replaced immediately upon burn-out, as having B+ drawn on the filament along with the regular filament current will cause it to burn too brightly with a failed pilot lamp, and eventually this filament will fail as well. At any rate, your radio has two pilot lamps from what it sounds like you're writing. What you must do now to get them to glow at full brightness is to put something in series with the filament in the 35W4 that serves for these bulbs. A rough equivilant to this filament is a 1 watt 47 ohm resistor. As far as tube connections, there should be a 47 ohm resistor with one side connected to the line cord, and one side connected to pin 4 of the 35W4 tube. Now the pilot lamps, which are strung in series, are connected, one end to where the 47 ohm resistor meets the line cord, and the other end to pin 6. Also connected to pin 6 should be a lead either directly connected to or through an additional resistor of small value to the plate of the tube (pin 5). This connection proceedure should yield bulbs of normal brightness. What I have done in the past, though, was to substitute the 47 ohm resistor with a dud tube in which the filament is still good, and linger this tube under the chassis. Since you are using a tube filament, which changes in resistance as it heats, where-as a resistor does not do so as much, you will get truer results. You can either use a 12AV6 tube (pins 3 and 4), or a dud 35W4 tube using pins 4 and 6. The 35W4 gives better results. Connect wires to this tube, and connect these wires to where the resistor would have been. Then wrap the pin part of the tube with electrical tape. A good tape to use is old fashioned electricians' cloth "friction" tape, as it holds well, and won't shrink or come loose like rubber tape. It is available at most True Value stores, and many other hardware stores.
::
::A word of caution is that you must connect your pilot lamps to the 35W4 tube exactly as stated above. These are the correct filament connections. If you connect the 35W4 tube in any other way, you will have poor results. If you connect the pilot lamps to say pins 6 and 3 or 3 and 4, you will have blown pilot lamps. I have seen quite a few basing diagrams in tube diagram books that label the pilot lamp tap on the wrong tube. Evidently they did not proof-read their work. The above way is the correct and only way to connect the pilot lamps.
::
::Hope this helps.
::
::Thomas
:::I have finished repairing an old Bendix model 300 and it works great except for one thing. It blows out the #47 pilot lights as soon as I turn the switch on. If I use the VARIAC and bring the line voltage up slowly, the lights get real bright but do not blow. I've there are no ballast resistors in this radio but the lights act like they are given a shot of very high voltage when the set is turned on (and line voltage is 115v). Could I have a loose connection causing arcing somewhere which would cause a current spike? Tubes all check out OK and voltages are in the green. I can't afford any more pilot lights nor can I keep the radio permanently plugged to my VARIAC. Any ideas??
:::
:::Thanks, Steve
At any rate, that's strange that the pilot lamps get dim again. They get bright initially, when the set is first turned on cold, because all the tube filaments are cold. When they are cold, they have less resistance, and more current flows through them. You'd think that since the pilot lamp ballast filament in the 35Y4 tube is also cold, it would also pass more current, and bypass this extra current around the pilot lamps. It usually doesn't, though, due to its small size, and they get bright for a split second. Then, after some of the tubes start glowing, and their resistance increases, the pilot lamps get dim. Once all of the filaments have reached full brightness, all resistances are stabilized, and the bulbs get brighter again. The final increase to full brightness is caused by the cathode of the 35Y4 starting to conduct current. As you remember, the rectifier is connected so that it conducts its current through the pilot lamps.
When the lights get dim again, does the radio change in performance? How long does it take before they go dim? This could be caused by some failure in the power section (resistor starting to open up when it gets hot), or a failure in one of the other sections, causing that failing section to not draw enough current from the rectifier to make the bulbs bright. The section that draws the most power is the audio output section (50L6 tube, or in your case, a loctal equivilant). The rectifier, itself, could be weak and failing. Usually rectifier tubes don't work well for one moment and then die down later, though. Sometimes gassy ones do. I'd look elsewhere, first. As for the resistor you replaced in the pilot lamp circuit, resistors usually increase in value when they warm up, which would make the bulbs brighter (more current would flow through the bulbs instead of bypassing through the resistor). On rare occasion you get a resistor that is made of a certain material that decreases in value as it warms. I forgot the name for the material that causes this. Anyway, listen to the radio as everything occurrs. The audio should be loud and undistorted, even after the bulbs dim down. If it gets mushy, your output tube could be gassy, or the control grid biasing resistor could be open, causing the grid to saturate with electrons--causing the tube to draw less current, dimming the bulbs, and also ruining audio quality. The bypass condenser between the first audio tube and output tube could be leaky, causing poor output tube performance. These conditions usually cause very poor audio quality, though, so if the audio is fine, they are likely fine.
At any rate, check all power resistors, and the ballast resistor first. Check for loose solder connections. If that doesn't solve anything, observe the radio's operation and see if anything else is a-miss. If the radio performs superbly, though, leave it alone (audio and rf sections). If this is the case, stick to power resistors, and maybe even electrolytics. If you have no hum, and the radio seems to be alright, electrolytics and tubes are not likely the problem (electrolytics cause hum problems, and low current, where-as tubes just cause low current draw when they become weak). When you replace a resistor, don't go using fancy resistors. Just use normal carbon composition resistors as originally used, and for the ballast resistor, use either a carbon or a wire wound resistor.
Take care,
Thomas
:::
::Thomas,
:Wow! quite a bit of info...are you an instructor? Yes, there are 2 #47 pilot lamps on this radio. they are wired in series with the resistor in parallel to them both. I replaced the resistor with a 5watt unit because I couldn't find a 2watt unit. The resistor is in series with the tube filaments and is connected between the power main and pin 1 on the 35Y4 tube. The Lights are connected on the power main side of the resistor and to pin 4 of the 35Y4 tube. It appears that the pin4 and pin2 (plate) are connected together and this is what appears on the schematic. Pin8 then is connected to all the other tube filaments. When the radio is turned on, the pilot lamps do not burn at full brightness until the radio starts to operate, but THEN....they grow brighter (what I would consider normal) and within a second or two they get dim again and stay that way???
::
: