Sorry - I meant from papa's circuit, using the +60V rail, 20dB gain, how many Watts would be delivered into 4 Ohm loads - now that you have found that it should perform well into a 4 Ohm load. My speakers vary between 4 and 2 Ohm on the low end. Thanks.
I absolutely agree that the first watt makes the most difference - as I am sure Papa does ;-). Having had many puny SE Triode amps driving tough loads, what a 300B can do with 8 Watts driven by an almost anemic 274 rectifier is still a stuff of legends.
But after years of "cobbling together" this and that tube stuff including OTL's, I am rediscovering the joys of solid state. I recently restored a Nakamichi PA7 and while it did things my SET's never could, I do miss the refinement and "liquidity" that seem so effortless on my 300B amps.
So when the VFET Part 1 came out with a promise of Part 2, I was ready to take the plunge and go beyond 30-yr old designs from Papa, I want his latest thinking and evolution. And when I watched him on the BAF2015 video, I was sold - I'm going to do this now, with parts I can get from Mouser.
72 Class A Watts should be plenty to do what I need, and if the amp is stable down to an occasional 2 Ohm, I can even expect (and will welcome) some true slam. This amp could be a very nice intersection between the sublime and the visceral!
I suspect this amp might be one of the best amps I will ever personally hear in my life.
Them's fighting words, my friend! I am very eager to see how this continues to evolve, and thank you for your sims - please keep 'em coming!
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My main speakers are very efficient, but I have a 2.5 way that hits 4 Ohms so I'll test it out on that too.
I think you would also very much like F6 if your speakers have some 2Ohm dips.
Build both. You can never have too many amps. There are many nice amps Nelson has given us, there's also the mini Sony Vfet amp and BA 3. Zen Mod seems to love M2 too.
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Once you have the chassis/heatsinking and power supply for this amp, go and populate pcbs for one channel of each. Throw one channel in at a time in same chassis and compare with the other amp on the other channel.
The wife never needs to know these sought of details. It's therapy for the mind. Hahahaha
I see that you've done this before!
In fact, as I was discussing this with another DIYAudio member privately, my plan is shaping up to be almost exactly as what you are describing: a 1.5kVA isolation transformer feeding a 1kVA Variac so I can change rail voltages at will, feeding the AC into monoblocks and if bias voltages are needed, supply them outboard with my bench supplies. This came to me before Papa's BAF2015 IXFN amp reveal, when I was planing to build the VFET Pt 2.
But the allure of a Class A SE amp that holds the promise of Triode-like sound but solid-state power really makes it logically a no brainer. So I am now on the hunt for caps and heat sinks that can cajole and tame this beauty of a beast.
Currently looking at 4x 68000µF and 500mm length of Austerlitz KS216 per side.
Yes, sir! "4x 68000µF and 500mm length of Austerlitz KS216 per side"...that is the current plan.
I've watched it quite a few times now, just to make sure I didn't miss any morsels of wisdom. The magic show stars at 28:30...
I normally listen to music at night time so not too bad at all really.
I don't leave the amp running all day
When I had my F4 DIY build, which had 180W total dissipation, after an hour of listening I had to open my window, because room temperature raised about 2-3 degrees of Celsius. And on hot summer days it was unbereable. Room is about 4x4 meters.
Our thermostat is set at 21°C all year round so the AC or heat kicks in when needed. But I already have the fan and am also considering liquid cooling - it's not that hard to setup and it's literally silent - since 200W hotplates are commonplace, and there are only 2 devices per side. The wife may veto that on looks though.
It's called ventilation.
Free of charge if it is cold air in at bottom, hot air out at top.
(close to 600W in 4x5)
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