I came across a local classified ad offering a few of these transformers for dirt cheap.
I have a solid state amp on my resume. I'd like to build a tube amp next. I haven't selected a design yet.
Can anyone comment on how suitable this power transformer would be and possibly suggest a compatible design (Simple SE or other)?
I have a solid state amp on my resume. I'd like to build a tube amp next. I haven't selected a design yet.
Can anyone comment on how suitable this power transformer would be and possibly suggest a compatible design (Simple SE or other)?
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No good, send them all to me.😱
Just joking, it looks like you could get roughly 530V B+ at 0.185 A for the plate supply ( less tube loss of tube rectification, etc).
That is sufficient for roughly 90W total power. You can get about 45W class AB(PP), or 22 W class A (SE).
Build monoblocks, or use two transformers, one for each channel if you want that much per channel.
I've been concentrating on low voltage amps (B+ = 265V) so I don't have any recomendations for the amp. I'm sure someone will chime in. Maybe a 6V6 20W/Channel design.
Just joking, it looks like you could get roughly 530V B+ at 0.185 A for the plate supply ( less tube loss of tube rectification, etc).
That is sufficient for roughly 90W total power. You can get about 45W class AB(PP), or 22 W class A (SE).
Build monoblocks, or use two transformers, one for each channel if you want that much per channel.
I've been concentrating on low voltage amps (B+ = 265V) so I don't have any recomendations for the amp. I'm sure someone will chime in. Maybe a 6V6 20W/Channel design.
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If they are cheap, pick up a couple. They are well suited for PP monoblocks, or stereo SE, maybe even lower power PP stereo.
A 530V B+ may be a little optimistic; I would guess 475-480V B+ using SS rectification. 730/2*1.41=515V, then subtract volts for R or L in CRC, CLC, etc.
A 530V B+ may be a little optimistic; I would guess 475-480V B+ using SS rectification. 730/2*1.41=515V, then subtract volts for R or L in CRC, CLC, etc.
If you happen to have a 250 mA choke, you could also make a choke-input power supply for a push-pull stereo 6V6 or 6BQ5 amp. With cap input, I think it would be great for the Simple SE (El34 or KT88).
Thanks for your help. I'll scoop up a couple of them.
The seller tells me that they came out of some "military tube audio / rf equipment". I'd expect that means decent quality.
The seller tells me that they came out of some "military tube audio / rf equipment". I'd expect that means decent quality.
I see no reason why it wouldn't run a Simple SE. I have used Mil surplus transformers like these with good results.
I like Tom Bavis' choke I/P filter idea. Used that way, the trafo being discussed would provide everything needed to power an "El Cheapo". Phase up the 5 V. and 30 V. windings and use the "35" V. composite to energize the B- hybrid bridge.
Not much in the way of a "fudge factor" cap. would be needed to bring the B+ rail up to a "perfect" 355 V. Perhaps a Hammond 193M would do as the 1st inductor in the cLCLC filter.
Not much in the way of a "fudge factor" cap. would be needed to bring the B+ rail up to a "perfect" 355 V. Perhaps a Hammond 193M would do as the 1st inductor in the cLCLC filter.
Would this transformer "plug-and-play" into the Simple SE design, or would other modifications be required?
I believe that it should be 'plug and play'.
This transformer has a 12.6 volt 4 Amp centre tapped secondary for the heaters. The Simple SE uses 6.3 volts for the heaters, but does not need a centre tap as it has an elevated reference circuit on the board. You should be able to use the centre tap and one 12.6 volt winding of the transformer, that will give you the 6.3 volts required. The output tubes needing the most heater current would be the KT88 with 1.6 Amps each. The ECC81 (12AT7) needs 0.3 Amp. This comes in at 3.5 Amps heater current total.
The Volts x Amps (VA) rating of the 12.6 volt winding is 50.4VA. With 6.3 volts, that works out to 8 Amps available. Since you will be using half of the winding to get the lower voltage, I am not sure if this halves the current back to 4 Amps, but in any case you are still safe. Someone more knowledgeable than me on transformers might like to speak up here to clarify.
They look like good transformers. Nice case, useful voltages and currents, and multiple primary taps to account for mains voltage variations. If they are cheap, I would pick up a few. Once you build your first amplifier, you will be hooked and want to build more!
Regards,
Chris
Instead of gambling, jumper the PCB to put the KT88 or other O/P tube heaters in series. The 'T7s are designed to work at either "6" or "12" V. Connect the heater bias voltage to the 12.6 V. winding's CT.
Yes, you would only use half of the 12.6 volt winding. Connect the center tap and one end (either one) to the 6.3 volt connections (T1-GRN) connections on the board. The winding is still limited by the current capability of its wire, which is 4 amps. That is enough for a Simple SE.
I don't have this exact transformer, but I have other similar mil surplus transformers like it. In this case it should work as intended. The mil stuff is over designed so it should outlast you and me. I have never blown one up. The only drawback is mounting them. You are stuck drilling some holes that are nearly touching, or cutting slots for the pins.
Ignore (don't connect) the 70 volt winding, and use the 125 volt tap on the primary for initial testing since a lot of line voltage in North America runs around 122 volts. After everything is working, measure the heater voltage and change the tap if it is below 6 volts.
Why would you make multiple trace cuts in a PC board when it is not needed. I spent a lot of time making sure that the layout was hum free, changing it might upset things. The 12AT7's can work on 12 volts, but the PC board layout isn't designed for it.
So it looks like I've been able to pretty much buy out the stock of these Transformers. I have a friend who's going to take a couple but I may still have more than I need.
I've had a few PMs with cash offers, but I'm more interested in a trade for a pair of decent SE Output Transformers. If anyone's interested in a trade, please send a PM and let me know what you've got.
I've had a few PMs with cash offers, but I'm more interested in a trade for a pair of decent SE Output Transformers. If anyone's interested in a trade, please send a PM and let me know what you've got.
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