801a amplifier

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Paul Barker
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#61 Re: 801a amplifier

Post by Paul Barker »

andrew Ivimey wrote: Sun Aug 29, 2021 10:05 am Again, nicely put. But as the cooling ashes get even cooler, vt62s/ 801 are a very very nice 2 Watts max in class A so would be in the same league as 46.

I once saw a 47 transformers coupled to pp 46s - nice idea!
Well the design intension of the 46 is to use class A a single 46 grid 2 with anode, interstage phase splitting It to pair of PP class b with both grids connected together at 0 volts bias. So that one tube would serve all purposes. The circuit is RCA pictured in the RCA data sheet for the 46. The 27 makes an ideal alternative as a voltage gain stage.

I must admit I did like the circuit and might add it to the bundle of mental crap slowly trying to delete my mind. But I would run the output valve class A PP and connect grid 2 to plate. But I cant find the interstage phase splitters, so the circuit Ive put in the 46 thread is it for now.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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andrew Ivimey
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#62 Re: 801a amplifier

Post by andrew Ivimey »

Good thinking, great sounds!!! Fingers crossed
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#63 Re: 801a amplifier

Post by Cressy Snr »

RhythMick wrote: Sun Aug 29, 2021 12:38 pm Thanks for sharing Steve. Impossible for a non sufferer like me to properly understand, not even close I'll bet. I hope you didn't take my post as trivialising the issue, if so I apologise.
No worries Mick. No apology necessary because you’ve done nothing wrong.

There’s no cure for depression/anxiety, but steps can be taken to live with it. The steps are far from easy, but the results are certainly well worth the effort required. Mindfulness and meditation is stonkingly good for anxiety in particular. It got me off the antidepressants. Two years free of medication came round this year.
15 years ago I wouldn’t have dared to discuss such things on a public forum. The fact that I and others now can, shows how far we’ve come come with talking about mental health. One good thing about the pandemic, is that it has brought mental health issues into the mainstream environment.
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Paul Barker
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#64 Re: 801a amplifier

Post by Paul Barker »

I’m resurecting this cosept, but in A1 only, Its a lot harder to build for A2 and the better distortion profile is found up to 3 watts per tube. By using parallel 801a’s my 5k OPT’s are just made for it.

The 801a heaters are so easy two 6 v 30 watt Torroids are more than adequate power for one parallel pair each, as theyre wound for 230v and my mains 242v The 801a’s see 7.4 voltes; perfect. You dont really want to starve Tungsten filaments.

A small core transformer heats both D3a’s out of the box to 6.4v: i’ll take that.

The 3 heater transformers are mounted, all three need hooking up and cathode resistors yet to mount with bypasses caps.

Ill take pics tomorrow.

d3a IT to output valves. all valves cathode resistor bias. Cheap resistors at first.

B+ and first stage 150v supply from it shall go on own chassis. Big 500 mA 725 volt transformer 5R4 GY potato masher or 5U4, choke input with that big 400mA 30 something henry choke I bought. Then Svetlana 572_160 shut reg, hopefully to settle regulated at 550v so operating point 500v about 50v for cathode bias. Thereon VR shunt regulated to 150v for d3a’s added into the signal section.

Im just building the signal stage for now.

46 experiment is on hold in the queue…… Im not capable of much at the present time, and was tying myself in knots about heater supplies, when the experiments with torroids in stock presented me with two perfect 801a transformers, I took that, one mountain in my head full of anxiety smashed. Anyway looking at the curves and better distortion but with a very low distortion effective power of 6 watts per channel, then 8 watts if you dont mind 3% distortion before crashing out. Might be nice, and I dont have to buy Lowther ex3’s yet! Diana watches every penny at the moment…….
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Paul Barker
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#65 Re: 801a amplifier

Post by Paul Barker »

"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#66 Re: 801a amplifier

Post by Paul Barker »

Image

Don’t get too excited these heaters and filaments are permanently heated and cathode resistors in place, awaiting bypass caps arrival.

The IT’s and OPTs not hooked up inputs and Panasonic pot not hooked up.

I’ll have to establish the 4ohm/8ohm connections and experiment with best sounding phasing, as I don’t know the anode from the b+ Make them swappable until I detect a better phase.

7.5 is running at a excellent result of 7.26v all four bottles. Nice.

The D3a not nice 6.7v but I may run these two at that long term they’ll probably outlive me. But it will be nice to experiment with two valves. I can probably get it down series connecting a spare 6.3v winding with the primary. But hay, I think I’ll not bother and that would compromise the screen.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#67 Re: 801a amplifier

Post by Cressy Snr »

I like those bright emitters. :)
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#68 Re: 801a amplifier

Post by Paul Barker »

The following havent come out in right order.

This salient points from the Glass Audio article I mentioned when Mark questioned parallel operation. I banked this knowledge when I recived my monthly comic that year. Sadly Glass Audio became Audio Express and after persevering with it for a few months I cancelled my subs.

I think Ive copied only a very small portion of the text to meet copy rules.

I may not have the amp at Owston, though I dearly hope I do. Its a work in progress and thes days Im on the verge of a breakdown, and the speach good friend Cressy gave about how his mind messes up his projects mine is worse. I have so much knowledge experiences an valves plus the associated parts, that Ive been round the houses and back just inside my head over this project.

If it doesnt show face this time, it will somehow soon even as a small gathering.

Im bringing this Glass Audio article at least, so read it while youre there. That is allowed, I bought it and I can let my friends read it.
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Nick
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#69 Re: 801a amplifier

Post by Nick »

I am not in any way saying that that's wrong Paul, but just because something is written in a book doesn't make it knowledge, just information. Lots of things are written in lots of books but you will get actual evidence by trying it yourself and seeing how it works for you.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#70 Re: 801a amplifier

Post by Cressy Snr »

Greg brought a parallel 2A3 to Owston years ago. It frightened the ruddy life out of me on a big production classical piece, such was its speed and jump factor. I liked it a lot. I think it used EH gold grid 2A3s IIRC, though Greg might correct me on that. Your 801As ought to be able to pull off the same trick.

BTW Paul,
It might be better for your mind, if you try and accept that like me, you are an inveterate tweaker and simply enjoy the process for its own sake.

Either refuse to engage with the Tormentor at your shoulder, who is probably endlessly judging and criticising you, or tell it to feck the hell off and mind its own damned business. I’ve found both those strategies to be surprisingly effective. I couldn't give a monkeys feck, how many times I mod something anymore. It's a better headspace to inhabit.
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Paul Barker
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#71 Re: 801a amplifier

Post by Paul Barker »

I hade really good progress today, stripped out an old project case. Mounted U19 valve bases. drilled for gynormous choke and layed out where black gates are going. unwound a 6v torroid for 4 volts. Most Ive done in a day for a while.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#72 Re: 801a amplifier

Post by Paul Barker »

The power supply is coming together.

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#73 Re: 801a amplifier

Post by Cressy Snr »

It’s looking suitably Steampunk Paul. :)
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#74 Re: 801a amplifier

Post by Paul Barker »

Coolio, and it’s all repurposed items so better for environment.

Cock on filament voltage.

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#75 Re: 801a amplifier

Post by IslandPink »

Did you get that choke when they broke up Dr. Frankenstein's lab ?
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