The AM Forum

Can anyone ID this filament transformer for the insulation or working voltage rating?

G.E. 7477922
5V@7A

or what  came out of?

thanks!

Well unless someone either knows that transformer or has data you are going to have to guess. I looked at the 5V filament rectifier tubes and an 866B is 5V @ 5A but it may have been used in a full wave circuit with two tubes. So maybe a pair of 3B24's.  What did you intend to use it for? I would suspect it is rated at least 2-3K volts.

If was used for HV rectifiers it would normally have HV insulators on the the 5 volt terminals.

Fred

It has insulators about 1/2" tall.

The job is for an 8020 vacuum diode's filament, so it is not the usual 866 or 872 which wants 5A. The filament current is stated as 5.5 to 6.5A.

I believe an open frame 5A unit would do it because it could cool itself.

It's for a negative peak limiter. It will see 7KV peaks if it's right to say that B+ of 3500V plus  100% modulation makes 7000V.

The goal is not to exceed 100% positive by any impressive amount, just prevent the B+ hitting 0V.

If Ashtabulah Bill could run tube diodes on this modulation limiter so can I. It's a question of finding suitable transformers. In the video it shows he used three 866's. He used them for ultramodulation but then he had a bigger modulator. I only want to clamp the negative peaks to 350V.

The diagram shows what I want to do. I'm putting the main parts on the chassis now.

You will need a xfmr with high voltage insulation.  10KV rating should be the lowest you should use.   Using SS diodes is a lot easier.

Fred

I will temporarily use a plug-in replacement for the 8020. It's almost twice as tall as the 866 type stick and the same diameter. More diodes inside I guess. It might need some resistance in series.

I agree it is easier with a SS rectifier.

nothings etched in stone, it might not even work in real transmitting. I tried the idea before with high idle on the 4-1000 and some audio and a battery supply sitting on a piece of thick plastic for the heater.

If nothing turns up I will have to find a  suitable trans. and wind a new secondary with some HV wire. I guess it is not that hard and then I can choose the insulation level by the spec of the wire and wrap the core in nylon tape or something to avoid sharp edges, correct?