Lockdown Valve Amp II

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SteveTheShadow
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Re: Lockdown Valve Amp II

Unread post by SteveTheShadow »

antonio66 wrote: Fri Mar 05, 2021 12:41 am ...I did not know the ECC82 was 'looked down upon' by you 'snooty' amp builders. I've bought a couple of GE 6189 (ECC82) Jan's to replace the cheap Chinese ones that are in the amp now.
Yes, it is not seen, by a significant section of the DIY community, as one of the better preamp valves. I was as guilty as anyone else: rejecting the thing without ever having heard a device with one in it. The real reason I moved to ECC82 If I’m being honest, was that the ‘superior’ 6SN7s I was using were not doing it, and I was too much of a skinflint to fork out for any more, especially given the ridiculous prices being asked for NOS valves.
I had a few old 1950s/60s ECC82 in my box, so a bit of work making up some adapters to reduce the hole size in the amp top plate and it was all systems go. No other component changes were required.
They are lovely valves as it turns out. I have no complaints at all about them. The sweet and detailed presentation they give is exactly what I’m looking for.
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Re: Lockdown Valve Amp II

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A lot of refinement, both electrically and cosmetically, has been done to this piece of steam engine hi-fi, since I last posted on this thread.

7 weeks down the line and we have come full circle back to EL34 power valves. I’d take these common or garden inexpensive valves over stupid priced 300Bs any day. The number of amplification stages has been slashed to two, courtesy of some Brimar EF80 pentodes strapped as triodes and the power supply is now a single setup feeding both stages with two sets of RC decoupling between the pre and power sections. Compared to how it was, the underside of the chassis is mostly air :lol: :
45FF312B-FABD-4B86-88C1-20C8644D44EE.jpeg
45FF312B-FABD-4B86-88C1-20C8644D44EE.jpeg (112.84 KiB) Viewed 1723 times
A cover has been fitted over the rear toroidal mains transformer, the power choke (grey box) has been changed for a potted 4H 200mA job, and the preamp stage power supply caps have been changed for a JJ 500V double can cap (front right)
The rectification is now a pair of 6CJ3 B&W TV damper diodes in a hybrid bridge arrangement.
It looks a lot better I think. Sounds nice too. :dance:
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CycleCoach (Sun Apr 25, 2021 7:46 am) • karatestu (Sun Apr 25, 2021 8:10 am) • Wonfor14 (Wed Jun 09, 2021 9:43 am)
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Re: Lockdown Valve Amp II

Unread post by antonio66 »

I bet it does sound nice, and if you're happy that's all that counts, looks good by the way :clap:

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Re: Lockdown Valve Amp II

Unread post by Fretless »

That is a seriously cool-looking amp, Steve. 8-)

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Re: Lockdown Valve Amp II

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Fretless wrote: Sun Apr 25, 2021 7:39 am That is a seriously cool-looking amp, Steve. 8-)
antonio66 wrote: Sun Apr 25, 2021 12:36 am I bet it does sound nice, and if you're happy that's all that counts, looks good by the way :clap:
Thanks chaps.
A lot of my amps in the past became more and more complex until they disappeared up their own backsides and got dismantled; the parts awaiting their next outing, and so the cycle carried on. That’s not to say I didn’t learn anything with each project, it’s just that I’m now fed up with the whole cycle thing and need to settle down long term with the system as it is. This is the reason I started to look at simplicity and aesthetics, in that order.

In terms of the simplicity of the audio circuit, I took a leaf out of Richard’s book and removed from the signal path, as much unnecessary clutter as I could get away with, which meant cutting the number of amplification stages. This significantly reduced the component count. There are now only two resistors and two caps in the audio cct signal path.

With a single ended amplifier however, the power supply is also in the signal path and the way you get that out of the way of the music is by using regulators. But the regulators also have a sound, so design choices there are critical if you don’t want the music to be strangled at birth.

Regs are a complex field and folks like Rod Coleman, Guido Tent, Nick Gorham (Lurcher) to name but three, have made the study and implication of them into a huge part of their work in valve electronics. I don’t have that level of expertise and have found that because of that, a simple, unregulated power supply sounds far better in one of my amps, than does one of my incompetent regulated efforts. :lol:

Simplicity without using regulators is not an easy undertaking, but help was at hand for me in the form of Duncan Munro’s PSUD computer software http://www.duncanamps.com/psud2/download.html. This has been available on PCs for years, but has only recently become available on the Mac. It’s a godsend TBH. I wouldn’t be without it now. It has certainly improved my design outcomes.

For example I was using a 10H choke in the power supply and simulated the 4H choke with a stepped current load where I programmed the current through the supply, to suddenly double after a predetermined time period had passed. This tells you how responsive the supply is and whether it rings after the step has occurred. With the 10H choke, the supply rang slightly and I couldn’t get rid of the ringing. With the 4H choke, there was a single overshoot then no ringing after the event. The fact that the 4H choke is potted in a grey box and looks a good deal better than the 10H choke was not allowed to influence the decision about whether or not to use it. The science prevailed of course. :lol:
Needless to say, the transient speed and bass response of the amplifier is much improved with the 4H choke, so the PSUD software exercise was well worth the time taken to do it.

One can keep trying different tubes for different sounds until the cows come home, but one has, in the end, to stop somewhere. I love the EL34 valve, and always seem to end up back with them, so I’ve developed this latest version to make the most of them, and to make it stick, I’ve got the aesthetics up to the job too.
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Re: Lockdown Valve Amp II

Unread post by SteveTheShadow »

OK,
Below are the schematics for those interested in that sort of thing.
Audio circuit:
Screenshot 2021-04-25 at 14.36.57.png
Screenshot 2021-04-25 at 14.36.57.png (94.26 KiB) Viewed 1574 times
Last edited by SteveTheShadow on Sun Apr 25, 2021 2:44 pm, edited 2 times in total.
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Re: Lockdown Valve Amp II

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Power Supply:
Screenshot 2021-04-25 at 14.36.09.png
Screenshot 2021-04-25 at 14.36.09.png (66.97 KiB) Viewed 1574 times
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Re: Lockdown Valve Amp II

Unread post by antonio66 »

I don't think you should pull yourself down over your previous effort, it looked good to me and I'm sure sounded good as well. I know you've made previous amps, so it's all a learning curve, and this is what you've ended up with, an amp that uses EL34's, a tube which you know you like. I bought a KT88 one from China, very pleased with it as well, and have also purchased a few pre amp valves to try having searched the internet, not tried any since they've all been posted to my uk address and I'm abroad at the moment. I haven't got my self any replacement power tubes yet, still undecided, but one question for you, how important is it to buy matching valves do you think?

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Re: Lockdown Valve Amp II

Unread post by SteveTheShadow »

Not pulling myself down really. I like DIY hi-fi. :)

If your amp is a push-pull unit, then matched valves are important. If it is single ended then matching is less important.
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Re: Lockdown Valve Amp II

Unread post by Wonfor14 »

SteveTheShadow wrote: Sun Apr 25, 2021 2:41 pm Power Supply:
Screenshot 2021-04-25 at 14.36.09.png
Hi Steve,

I was wondering why did use AC on the heaters? Would slow start DC be better?
I love the look.
On the Cathode Follower design could you use a Transzobe ( spelling wrong) instead of series Zeners?
And the next silly question I love the Poly Caps, but I find the caps from ITW Paktron better, you thoughts please. Thank you.

Best Col

https://paktron.com/

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