Hello All,
I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.

Thanks,

Dave

Hi Dave

Best to use a 5 or 6 volt winding for your 2 volt supply. After the rectifier diodes voltage should be regulated by a LM317. The LM317 requires a min voltage between input and output to regulate.

Might be hard to find 180-0-180 volt transformer winding? Little higher will work using an 80 rectifier. You can always drop voltage with a wire wound resistor. A battery powered radio doesn't require as much B+ current so a resistor won't get as hot as in AC radios.

Norm

:Hello All,
: I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
: What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.
:
:Thanks,
:
:Dave

Dave,

If I figured them up correctly, the current draw of all the filaments will be about 570 milliamps so may need some sort of a heatsink on the LM317.

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

:Hi Dave
:
: Best to use a 5 or 6 volt winding for your 2 volt supply. After the rectifier diodes voltage should be regulated by a LM317. The LM317 requires a min voltage between input and output to regulate.
:
: Might be hard to find 180-0-180 volt transformer winding? Little higher will work using an 80 rectifier. You can always drop voltage with a wire wound resistor. A battery powered radio doesn't require as much B+ current so a resistor won't get as hot as in AC radios.
:
:Norm
:
::Hello All,
:: I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
:: What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.
::
::Thanks,
::
::Dave

Radiodoc,
Why not then use a separate 2.5v filament transformer? That should be 3.5 volts, no load, after rectification and filtering. A resistor may bring it down to 2 volts or even 2 1N40x diodes in series. That should do it.
I'll do this after removing the mess of wasp nests from the chassis. Have you ever had a chassis that was loaded with long abandoned wasp nests?

Thanks,

Dave

:Dave,
:
:If I figured them up correctly, the current draw of all the filaments will be about 570 milliamps so may need some sort of a heatsink on the LM317.
:
:Radiodoc
:***********
:
::Hi Dave
::
:: Best to use a 5 or 6 volt winding for your 2 volt supply. After the rectifier diodes voltage should be regulated by a LM317. The LM317 requires a min voltage between input and output to regulate.
::
:: Might be hard to find 180-0-180 volt transformer winding? Little higher will work using an 80 rectifier. You can always drop voltage with a wire wound resistor. A battery powered radio doesn't require as much B+ current so a resistor won't get as hot as in AC radios.
::
::Norm
::
:::Hello All,
::: I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
::: What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.
:::
:::Thanks,
:::
:::Dave

:Radiodoc,
: Why not then use a separate 2.5v filament transformer? That should be 3.5 volts, no load, after rectification and filtering. A resistor may bring it down to 2 volts or even 2 1N40x diodes in series. That should do it.
: I'll do this after removing the mess of wasp nests from the chassis. Have you ever had a chassis that was loaded with long abandoned wasp nests?
:
:
:Thanks,
:
:Dave
:
::Dave,
::
::If I figured them up correctly, the current draw of all the filaments will be about 570 milliamps so may need some sort of a heatsink on the LM317.
::
::Radiodoc
::***********
::
:::Hi Dave
:::
::: Best to use a 5 or 6 volt winding for your 2 volt supply. After the rectifier diodes voltage should be regulated by a LM317. The LM317 requires a min voltage between input and output to regulate.
:::
::: Might be hard to find 180-0-180 volt transformer winding? Little higher will work using an 80 rectifier. You can always drop voltage with a wire wound resistor. A battery powered radio doesn't require as much B+ current so a resistor won't get as hot as in AC radios.
:::
:::Norm
:::
::::Hello All,
:::: I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
:::: What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.
::::
::::Thanks,
::::
::::Dave

You can very easily connect a 2N3055 transistor to a LM317 and get Amperes of current, and if the 317 is on the same heat sink as the transistor, the thermal protection that the 317 provides.

No, I have never had to clean an abandoned wasp nest out of a receiver, but a few occupied ones and a few rats that got into the transmitter and connected with 9,300 Volts and exploded, after overloading the plate power supply, set to trip at 2.5 Amps, if I remember correctly.
Lewis

Norm,
I have lots of LM317s. I didn't know it could supply enough current for the 6 filaments.
So what you're saying is that I need a "nothing fancy" power transformer with a 5 volt winding for the 80 and a 6.3 volt winding for the 2 volt supply. How many mA is enough for the B+ in this set? Probably any Hammond will work. It looks like 240-0-240 is the smallest that has two filament windings (5 and 6.3).

I'm using the 80 or 5Y3 or 5Y4 because that looks better with Antique Radios. The little rectifier diodes in the filament supply can be hidden. I can probably hide the LM317 as well.

Thanks,

Dave
:Hi Dave
:
: Best to use a 5 or 6 volt winding for your 2 volt supply. After the rectifier diodes voltage should be regulated by a LM317. The LM317 requires a min voltage between input and output to regulate.
:
: Might be hard to find 180-0-180 volt transformer winding? Little higher will work using an 80 rectifier. You can always drop voltage with a wire wound resistor. A battery powered radio doesn't require as much B+ current so a resistor won't get as hot as in AC radios.
:
:Norm
:
::Hello All,
:: I will soon be working on a Crosley 27 (Same circuit as 28). I want to build an external power supply for it. B+ is 180 volts and filament is 2 volts DC. I am going to use an 80 for the rectifier. I don't like to bother with inrush current or worry about it. What should the filament winding voltage be? Is 2.5 or 5 ok with a suitable current limiting resistor? For that voltage I will I'll use a solid state rectifier. For B+ should the transformer be 180-0-180 or higher? I have built these power supplies before but I always ask for advice when choosing the power transformer to help make the choice easier.
:: What a mess! This radio has a cabinet that has come apart, there are things inside that look like ancient hornet's nests that have to be vacuumed out, and I have to rewire it. All the tubes are missing but they're easy ones to get. The first thing I'm going to do is clean, rewire and test with batteries before I build the power supply. 20 dollar store 9 volt batteries should work fine for the B+ and somehow I'll come up with the 2 volts for the filaments.
::
::Thanks,
::
::Dave

You definitely want a little more than 180 volts so that you can filter it well (200 should work well). Most of my portables use 1/4 watt resistors in the B circuit--to supply the main voltage to ALL of the tubes. In my Zeniths, a value around 2700 ohms is typical for the main B+ filtering resistor. A few days ago I built a little FM radio that had parallel push-pull output (and it only picked up channel 4...yay!). That was using 1.5 volt subminiature pentodes and triodes. I used 1/8 watt resistors throughout, and none of them got even remotely warm. None of the tubes really got warm, either. Perhaps the output ones did. I wonder if it was my imagination, though. I was running everything either at 45 or 90 volts, depending on when I was doing whatever I was doing. I finally decided on 45 volts simply because everything worked better that way. At 90 volts, though, none of the resistors got warm at all.

If you purchase a 200 to 250 volt transformer with a separate 5.0 volt winding and a 6.3 volt winding, you should be good to go. Use the 6.3 volt winding for the filaments.

T.

Thomas,
The tubes this radio uses are 31s and 32s. There are 3 of each and it's a TRF. I guess it's somewhat similar but it's not a Superhet. I'm pretty sure that there were superhets at the time but this one was a TRF.

Dave
:You definitely want a little more than 180 volts so that you can filter it well (200 should work well). Most of my portables use 1/4 watt resistors in the B circuit--to supply the main voltage to ALL of the tubes. In my Zeniths, a value around 2700 ohms is typical for the main B+ filtering resistor. A few days ago I built a little FM radio that had parallel push-pull output (and it only picked up channel 4...yay!). That was using 1.5 volt subminiature pentodes and triodes. I used 1/8 watt resistors throughout, and none of them got even remotely warm. None of the tubes really got warm, either. Perhaps the output ones did. I wonder if it was my imagination, though. I was running everything either at 45 or 90 volts, depending on when I was doing whatever I was doing. I finally decided on 45 volts simply because everything worked better that way. At 90 volts, though, none of the resistors got warm at all.
:
:If you purchase a 200 to 250 volt transformer with a separate 5.0 volt winding and a 6.3 volt winding, you should be good to go. Use the 6.3 volt winding for the filaments.
:
:T.

Dave

You don't need a lot of current for filaments or B+. 32's draw .06 amps while 31's draw .13 amps. That will be less than 600 ma for all tubes.

B+ wouldn't be more than 30 ma with your 31 tunes drawing full current. The radio probably draws closer to 20 ma.

A small transformer will work and look good. As was suggested you could rectify filament voltage and just filter it. This might leave some hum. Best to use a regulator. Besides setting voltage it removes ripple.

Norm

:Thomas,
: The tubes this radio uses are 31s and 32s. There are 3 of each and it's a TRF. I guess it's somewhat similar but it's not a Superhet. I'm pretty sure that there were superhets at the time but this one was a TRF.
:
:Dave
::You definitely want a little more than 180 volts so that you can filter it well (200 should work well). Most of my portables use 1/4 watt resistors in the B circuit--to supply the main voltage to ALL of the tubes. In my Zeniths, a value around 2700 ohms is typical for the main B+ filtering resistor. A few days ago I built a little FM radio that had parallel push-pull output (and it only picked up channel 4...yay!). That was using 1.5 volt subminiature pentodes and triodes. I used 1/8 watt resistors throughout, and none of them got even remotely warm. None of the tubes really got warm, either. Perhaps the output ones did. I wonder if it was my imagination, though. I was running everything either at 45 or 90 volts, depending on when I was doing whatever I was doing. I finally decided on 45 volts simply because everything worked better that way. At 90 volts, though, none of the resistors got warm at all.
::
::If you purchase a 200 to 250 volt transformer with a separate 5.0 volt winding and a 6.3 volt winding, you should be good to go. Use the 6.3 volt winding for the filaments.
::
::T.

Yeah, an LM317 will work well for the filaments, and shouldn't get too warm.

...and regarding #31 and #32 tubes, they are similar in performance and current draw to 1LA6s, 1LH4s, 1LN5s, and 1LB4s, and their octal equivilants. You can expect your current draw to be very much similar to that found in a 3-way portable radio. The current draw for my Zenith 5-G-500 from the battery is listed as 1 watt. Amazingly low! I don't know if that includes filaments, but wattage of the filaments would be from .36 to .45, so I guess it does. (1.5 x .3 amperes = .45 watts ....if strung in parallel....if in series, 6 volts x .06 amperes = .36 watts).

Actually for the 5-G-500 it would be .36 watts regardless of whether they were wired in parallel or series. I kept wondering why there was a difference, but it was because I was counting 5 tubes instead of 4 whenever I'd do them in parallel (rectifier doesn't count).

T.

Hello All,
I still have this radio sitting around and I want to get it working. In addition to a power supply, I'm going to need a speaker transformer for it. I have a bench top supply for testing the radio for B+, and I have an LM317. I have a 6V car battery. How do I construct the circuit so that I can connect exactly 2V to the radio for filament? 220 ohms from adjust to output and then 110 ohms? V in is going to be 6V. I'll figure it out.

Dave

:Actually for the 5-G-500 it would be .36 watts regardless of whether they were wired in parallel or series. I kept wondering why there was a difference, but it was because I was counting 5 tubes instead of 4 whenever I'd do them in parallel (rectifier doesn't count).
:
:T.