PP transformer for SE use

[Brian Donaldson]

I had an idea to use a PP transformer in a SE amp by using one half of the primary with the triode like any SET amp, and a current source feeding the same curent into the other end of the tansformer. My thoughts were that I could use a much smaller and cheaper ungapped PP transformer, but wanted to ask if anyone has done this and how did it sound. (actually, I could use a much bigger triode as I can't find a SE transformer over 50W)

I wanted to avoid parafeed because of the big cap needed.

[Tweeker]

On Plitron's site under special designs I found this:

PAT HQ5090 Application: Svetlana SV572 Triode 90 Watts

This Single Ended output transformer is intended for paralleled Svetlana SV572 triode tubes, with a primary impedance of 2.5 or 5 kOhm, depending on secondary loading. Secondary impedances are 2, 4 and 8 Ohms. The -3dB bandwidth is from 8 Hz to 43 kHz with a high frequency Q-factor close to 0.5 (critical damping). The insertion loss is an extremely low 0.15 dB ensuring no loss of audio power and creating excellent damping at the low frequency end of the power spectrum. The DC current capability is 400 mA maximum. This transformer is designed for no overall negative feedback applications, completely relying on the tube characteristics for the purest sound quality.

I couldnt find any further information though.

[Tweeker]

Hammond 1642SE
75watts
5,000ohm impedance
300 ma. max DC bias
4-8-16 ohm taps
3,500 V RMS hipot
28 pounds

[Brian Donaldson]

Thanks

$611 each for the Plitron...ouch

I was looking for 200watts worth for an 833A, but if I can't find the iron at a reasonable cost, I may just do an OTL 6C33C x6 amp.

I was thinking maybe the 280W they sell for PP. Any comment on counter-biasing a PP tranny

I need 1800 ohm or so 400 to 500 ma.

[Giaime]

Why not try to parallel two Hammond 1642se?

[Fuling]

I´ve had similar ideas but never tested anything out.
Maybe pentode for the CCS and a similar pentode (but triode wired) for the signal side?

[Brian Donaldson]

ccs side, I'll go sand. Maybe even OP amp servo controlled mosfet tuned to low frequency like .5 hz.

I may have to try it on a smaller scale first.

[Tweeker]

You might find this thread interesting.

DC compensated SE output transformer.

[Tweeker]

Somewhere there a discussion of an amp with a triode on top and pentode on the bottom, with the gain mostly coming from the triode, but I cant find it.

[tubelab.com]

I was looking for 200watts worth for an 833A, but if I can't find the iron at a reasonable cost

Now that's my kind of amp. I have just about decided to use the Hammond 1642SE. I might go for custom Electra-Prints if I have the bucks. This amp will have to wait till early next year though.

I tried the custom transformer route, through a transformer winder who builds good 300B transformers, but the 200 watt SE transformer didn't quite work as good as his computer program said it would. It is good enough for a 200 watt SE guitar amp, which is currently being breadboarded.

The CCS load on the other half of the transformer trick does work. I tried it at the 8 watt level using a 300B on one leg of the transformer, and an IXYS 10M45 on the other leg. To get 200 watts out of an 833A, I had to run 1500 volts. That voltage tends to turn silicon back to sand if you are not careful. I have been experimenting with hybrid CCS's. There is a thread discussing the results of a few peoples experiments along these lines.

Active load output stage