I'm working on a circa 1929 Victor TRF radio that lost its power (fil. & HV)transformer. Should mention it's for an older lady and it was her father's--it's all gratis on my part. The fils for the four '26' tubes were all on one winding, in parallel, with no dropping res. needed. I've had to split them out, using mult. transformers, and use dropping res. as needed; 2 tubes per trans. My grid biases seem to be messed up. Even the first tube, whose grid has the antenna, vol. pot. and a coil hanging off of it has 0 grid volts, (sb 6 or 8) regardless of what I do. My gain per stage is between 1 and 2.

I'm pulling out my hair and can't spare much! I'd appreciate any help, and have a hand-drawn schematic of my changes available to scan and email, should anyone need more details. Thanks, everyone. I've never used a forum like this and I'm eager to get this project off of "dead center".

Just a short suggestion: when I have had to come up with low volage high current filament transformer, I rewind a transformer I have on hand. Say you have a transformer that is rated at 6.3 volt 2 amp, that would give you a rating of 12.6 watts. If you remove the 6.3 volt winding and replace it with fewer turns of a heavier gauge wire and rewind it for 1.5 volts, you can draw a little over 8 amps from the same transformer. This is fairly easy to do since the secondary on many transformers is usually on top or on a seperate split bobbin. You don't have to take apart the laminations. Just count as you unwind and that will give you the approximate volts per turn. I usually use THHN stranded wire because I can easily loop it through the core. Give it a try it works much better than heat generating resistors and it simplifies things. I had to do this on my R-32 "whale mouth" and it worked great. I was able to use the filament structure as shown in the schematic. Just a hint that I hope is usefull to you.

MRO

:I'm working on a circa 1929 Victor TRF radio that lost its power (fil. & HV)transformer. Should mention it's for an older lady and it was her father's--it's all gratis on my part. The fils for the four '26' tubes were all on one winding, in parallel, with no dropping res. needed. I've had to split them out, using mult. transformers, and use dropping res. as needed; 2 tubes per trans. My grid biases seem to be messed up. Even the first tube, whose grid has the antenna, vol. pot. and a coil hanging off of it has 0 grid volts, (sb 6 or 8) regardless of what I do. My gain per stage is between 1 and 2.
:
:I'm pulling out my hair and can't spare much! I'd appreciate any help, and have a hand-drawn schematic of my changes available to scan and email, should anyone need more details. Thanks, everyone. I've never used a forum like this and I'm eager to get this project off of "dead center".

Since 26 tubes are filament type you will end up with bias & hum problems rewiring or using multiple transformers. Mark has a good suggestion. It only takes a few turns of heavy wire for 1.5 volts.

Check near the bottom of this list. There will be power transformers available with 1.5 & 2.5 volt windings.

http://www.oldradioparts.com/2a23efl.txt

Norm

:Just a short suggestion: when I have had to come up with low volage high current filament transformer, I rewind a transformer I have on hand. Say you have a transformer that is rated at 6.3 volt 2 amp, that would give you a rating of 12.6 watts. If you remove the 6.3 volt winding and replace it with fewer turns of a heavier gauge wire and rewind it for 1.5 volts, you can draw a little over 8 amps from the same transformer. This is fairly easy to do since the secondary on many transformers is usually on top or on a seperate split bobbin. You don't have to take apart the laminations. Just count as you unwind and that will give you the approximate volts per turn. I usually use THHN stranded wire because I can easily loop it through the core. Give it a try it works much better than heat generating resistors and it simplifies things. I had to do this on my R-32 "whale mouth" and it worked great. I was able to use the filament structure as shown in the schematic. Just a hint that I hope is usefull to you.
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:MRO
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::I'm working on a circa 1929 Victor TRF radio that lost its power (fil. & HV)transformer. Should mention it's for an older lady and it was her father's--it's all gratis on my part. The fils for the four '26' tubes were all on one winding, in parallel, with no dropping res. needed. I've had to split them out, using mult. transformers, and use dropping res. as needed; 2 tubes per trans. My grid biases seem to be messed up. Even the first tube, whose grid has the antenna, vol. pot. and a coil hanging off of it has 0 grid volts, (sb 6 or 8) regardless of what I do. My gain per stage is between 1 and 2.
::
::I'm pulling out my hair and can't spare much! I'd appreciate any help, and have a hand-drawn schematic of my changes available to scan and email, should anyone need more details. Thanks, everyone. I've never used a forum like this and I'm eager to get this project off of "dead center".

www.tubesandmore.com also sells a power transformer with two 2.5 volt windings and one 5.0 volt winding. If dropping resistors are used, there should be one per side of the winding, each one being half the total resistance required. This will keep the center of your winding in the center, allowing you to use the center tap as a B- tap. Otherwise, if you don't keep the winding centered (use a resistor on only one leg, for instance), you will have to center the B- another way. One way would be to use a 40 ohm wire wound potentiometer with its end terminals tied to the tube filament terminals, and its center terminal tied to B-. Adjust until hum is at a minimum.

Thomas