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Re: Small Push-Pull Amp.

Posted: Fri Jul 19, 2019 10:15 pm
by Cressy Snr
Paul Barker wrote:
Fri Jul 19, 2019 9:28 pm
Nowt wrong with triode strapped valves. Some prefer gk71 over gm70. I liked 813 triode connected as much as I loved 211 for their unique stand out extra not heard in most amplifiers. Entirely different to each other yet only mood or tastes depending on which way your preference lies.
Just having a laugh Paul. My 13E1 OTL is a triode strapped Tetrode after all.

Re: Small Push-Pull Amp.

Posted: Fri Jul 19, 2019 10:27 pm
by Cressy Snr
6336A curves:
Image

260 ish on the anodes and 90mA idle current at 80 ish Vk looks decent to me.

2K5 loadline.

Re: Small Push-Pull Amp.

Posted: Sat Jul 20, 2019 12:58 pm
by Cressy Snr
Some working out (not mine, but why reinvent the wheel)

Image

The blue line gives 26.1W plate dissipation per section, plus the 31.5W of heaters. This means having to shift 83.7W of heat from a bottle the size of a KT88
The green line at 23.5W per section is a little cooler at 78.5W to manage. The valve is designed to manage this, but it’s a bit warm. I’ll probably go for the green line, even though the max distortion is slightly higher at full power.

Driver needs to swing 160V pk-pk, so a simple 6SN7, or 12AU7 cascade will easily manage it on a shallow load line.

Re: Small Push-Pull Amp.

Posted: Sat Jul 20, 2019 2:17 pm
by izzy wizzy
I see you're plotting as a single valve. So is this a SE amp now?

I've just been playing around with composite curves for PP amplifiers for the first time for the GM70 PP amp and I think it comes out as different to playing around with single sets of curves.

Cheers,
Stephen

Re: Small Push-Pull Amp.

Posted: Sat Jul 20, 2019 2:40 pm
by Cressy Snr
izzy wizzy wrote:
Sat Jul 20, 2019 2:17 pm
I see you're plotting as a single valve. So is this a SE amp now?

I've just been playing around with composite curves for PP amplifiers for the first time for the GM70 PP amp and I think it comes out as different to playing around with single sets of curves.

Cheers,
Stephen
Yes, It’s now SE. I have some Hammond 1627SE output transformers off Steve S (which I still need to pay him for) that are good for 130mA DC and its a shame to leave them lying about. I also have experience with the 6336A and know how good it sounds as a single stereo amplifier valve.

I could have gone big with the 1950s 13E1s I have, but you’re talking 200mA before they start singing in SE; which would have meant having another custom pair of OPTs made to replace the Majestics that I sold, years ago. I don’t have that sort of dosh to chuck around these days.

I’ll have to start another thread.