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sorenj07 21st October 2007 09:32 PM

Triodes that would like a 10K a-a OPT?
Are there any reasonable (price, availability) power triodes that would like a reasonably high primary impedance on such a transformer? I'd been thinking maybe the 6S19P but am open to other options such as a 6EM7 and 6BL7, though 6BL7's seem a little rare...

Eli Duttman 21st October 2007 10:28 PM

Triode wired 6V6s and close relations love 10 K trafos. See Poindexter's "Musical Machine".

sorenj07 21st October 2007 11:51 PM

I might have to do the Musical Machine. I'd probably use some 5V6 tubes.

As for the driver tube: what would be best? The closest substitute I can think of is a 6N7S in that it has a similar gain (35 vs 47), but the 6N7S has a plate resistance of 11K versus 6.7K for the 5865. Is this likely to be an issue?

Eli Duttman 22nd October 2007 12:18 AM

The twin triode is a 5965. High gm is a consideration in a differential splitter. I think that rules the 6N7 out. Of late, Poinz has been experimenting with hand matched 6GK5s in the splitter.

BTW, "El Cheapo" owes much to Poinz's design. We went for a much lower price point. Please notice that, like the 5965, the 12AT7 is a high gm type.

sorenj07 22nd October 2007 04:36 AM

Thanks! I think I'll actually go with 6S19P's, they offer the best price/power ratio for triodes I've seen. I've also been confirmed in my suspicion that 10K a-a actually is reasonable. If you draw the load line you'll see what I mean.

The OPT, without voltage measurements yet.

sorenj07 22nd October 2007 07:18 AM

I might try triode-wired 6AG7's. Looking at the datasheet for the Russian equivalent, the 6P9, things seem pretty hopeful. A 6N23P/6N1P driver stage Musical Machine-style with a negative long-tail supply seems like it should work fine, with a bit of headroom for feedback. And, if I hate the way the amp sounds after tweaking it constantly, I can always turn it into a real Musical Machine by subbing in 6V6's and a 5965.

sorenj07 22nd October 2007 07:12 PM

Update! Measured the various impedances of one of the OPT's (I assume it holds true for both) and got some interesting numbers.

I guess it's "Triodes that would like a 7.5K a-a OPT?" now :smash:

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