2A3 "Pink SET" Amp Rebuild.

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steve s
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#91 Re: 2A3 "Pink SET" Amp Rebuild.

Post by steve s »

My experience with simple power supplies & se valves Steve is that with simple music it sounds rather nice and lush..
It's when you play some heavy rock at volume, it merges into a bit of a mess...
Which tells me its not quite right.
The separate supplys I'm using work-
There is more clarity and detail to be heard.
I was very please with the px25 at the wam show once it warmed up ( its not had a good blast for ages). But I still need to do some work on simplifying the supplys as I think I've lost something on the way.
It's interesting my little nva amp which looses out in outright clarity but has a slightly better bass has no trouble with whatever is played through it.
in my view this is down to the fact its drawing very little power with my speakers. Probably it would sound different with a pair of 85 db speakers and cranked up?
It will be interesting to see what you find.. but you may be converting the amp into one that works worse at higher volume ? Time will tell
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#92 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

RhythMick wrote: Thu Apr 12, 2018 7:53 am I'd be interested in the circuit diagram if you have one
I don't have the circuit; it just came out of my head.
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#93 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

steve s wrote: Thu Apr 12, 2018 8:18 am My experience with simple power supplies & se valves Steve is that with simple music it sounds rather nice and lush..
It's when you play some heavy rock at volume, it merges into a bit of a mess...
Which tells me its not quite right.
The separate supplys I'm using work-
There is more clarity and detail to be heard.
I was very please with the px25 at the wam show once it warmed up ( its not had a good blast for ages). But I still need to do some work on simplifying the supplys as I think I've lost something on the way.
I'm not talking about seperate power supplies in this instance Steve. I know they work a treat and give better access to the music than a single power supply does.

What I'm talking about here is a single power supply and just removing components from the signal path and getting a big increase in musical enjoyment. It really is uncanny, the damage that components can do to the music signal.

The jump in quality I got from the SE amp component removal regime is bigger than the increase I got with the DIYNVA amp and I find that really interesting.
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Ant
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#94 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Ant »

Maybe thats why monkey drd amps sound so nice. Like that monkey px25
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#95 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Having had another look inside the SET, because I'm about to fit an ground lift switch, let's forget the decoupling business, 'cos that isn't it. I think I'm going fooking senile! I shouldn't be allowed to carry sharp scissors, let alone be in the vicinity of high voltage. :roll:

Jeez.

I'll be back in a short while :lol:
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#96 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Right!
Below is what I did:
Image
The grounding scheme has been completely redone as a bus bar system, with ground lift facility.
The RC filters between the stages have been removed and the HT is supplied by bus bar distribution.
The bus bar feeds the HT top down to the six 200uF/500V caps (three per side)

The red wire at the top cap is the HT feed to the output transformer
The large, metal clad resistor feeding the driver valve, has its supply side terminated at the middle cap
The 15K Mills resistor is supplied from the bottom cap and feeds the input stage valve.

This arrangement is replicated on the other channel's three power supply caps.

Don't think it could get any simpler than that.
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#97 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

short of removing the cathode bypass caps, but that ain't happening.
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#98 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

RhythMick wrote: Thu Apr 12, 2018 7:53 am I'd be interested in the circuit diagram if you have one
Here it is, showing one channel:
Image

This includes the simplified power supply and ground lift switch.
Three caps per side and that's your lot. Simple, naive, like you've given a rookie kid a bunch of components and said "build something".

Ashamed to post it I am. I can hear the WTFs and the howls of laughter about the power supply. But it all works beautifully together, playing music like no other valve amp I've built. Don't know why it does that, but it's magic.

Where it says "from rectifier 385V" it should say "from choke" but I can't be arsed to alter it now. And a 15K resistor label seems to have come adrift, ignore it :)

Oh and FFS don't use ANY 2A3 other than the JJ 2A3-40W, not unless you enjoy glowing anodes!
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andrew Ivimey
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#99 Re: 2A3 "Pink SET" Amp Rebuild.

Post by andrew Ivimey »

Ive got four of those monsters in the cupboard - why not just put them in my Thorsten Monkey... having first swapped out the heater transformers, a.c. only at Bedford Towers
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#100 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

Just played this wonderful, wonderful deep soul record, from 1966:



Jimmy Holiday died in 1987. What a voice!
I need a lie down after that....... :cry: :cry:
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RhythMick
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#101 Re: 2A3 "Pink SET" Amp Rebuild.

Post by RhythMick »

Good for you. Nothing beats that moment when you play music through it and it reaches into your soul.

"from choke" so basically it's an LC, with the 3 smoothing caps in parallel? Or is that changed because each feeds a valve? If you had a 600uF cap and all 3 Fed from it would that be the same?

What's the choke?
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andrew Ivimey
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#102 Re: 2A3 "Pink SET" Amp Rebuild.

Post by andrew Ivimey »

Its all to do with decoupling but, I'd be tempted to radically cut the microfarads to see how it changes the sound. Could be radical, could be pants but worth a try, Shirley.
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.
Cressy Snr
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#103 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

andrew Ivimey wrote: Thu Apr 12, 2018 9:57 pm Its all to do with decoupling but, I'd be tempted to radically cut the microfarads to see how it changes the sound. Could be radical, could be pants but worth a try, Shirley.
Could reduce the mFs.
The original build of this was a parts bin special. I was on a budget and had to use what was available. Even the OPTs are not mine. They were scrounged from Steve S. May order some smaller caps. I reckon the thing might be a bit slugged at the moment but then again....
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#104 Re: 2A3 "Pink SET" Amp Rebuild.

Post by Cressy Snr »

andrew Ivimey wrote: Thu Apr 12, 2018 9:57 pm .....I'd be tempted to radically cut the microfarads to see how it changes the sound. Could be radical, could be pants but worth a try, Shirley.
OK,
So I cut the total capacitance by half, which was easy to do because the JJ caps are dual-section jobbies, with 2 off, 100uF units in the one can, with a common negative. All I needed to do was to disconnect one of the sections from the power bus at each can. The result is more music; simple. Those gorgeous female vocal tones that DH SET bods rave about are present, so that can't be bad, can it.

Looks like my habit over the last couple of years, of piling in the capacitance has turned out to be a load of bollocks. OK perhaps with class AB push pull, but completely the wrong approach with single ended amps.

Now then,
Anyone remember the Ultrapath connection.
Did it ever deliver? It's all a bit of a long time ago now, has anybody still got one in their amp?
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andrew Ivimey
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#105 Re: 2A3 "Pink SET" Amp Rebuild.

Post by andrew Ivimey »

for the sake of experiment I'd be tempted to go down to 10mfd - this may be too far but can you hear the difference?

Ultrapath... vaguely familiar - what was it all about?
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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