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Leak Stereo 20

Sounds as if your original GZ34 has one side faulty or at least very weak. This would mean your full wave rectification was actually half wave which would explain the lower voltage and the imbalance would cause the transformer hum.
 
chiily said:
I swapped the GZ34 over to the Mullard and the transformer hum has come back, and the voltages are all lower, same as the ones in my previous post. Looks like the Mullard is bust :(
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Commiserations, but these things happen, old chap. Just because people ask (and others pay) a fortune for Mullard GZ34s doesn’t necessarily mean they last forever. Mine expired (STA15) a couple of years ago. It was replaced by a Bentley (made in the same Blackburn factory, but cost about a quarter of the price asked for a Mullard because it had different printing on it.)
 
It certainly does look like it is broken. The good thing is that I never heard the amp with the Mullard GZ34, so I don't know what I'm missing. I do keep an eye on ebayed Mullard NOS GZ34, the cost just keeps on going up. Maybe one day... There's a Harma modern GZ34 in there atm I'll see how it gets on with the Sovtek EL34s.

Finally tomorrow night I'll plug the ST20 into the 57s...will it be up there with the Quad IIs?
 
I wouldn’t fret about it too much. When my Radford was being serviced no measurable difference was noticed with a Mullard or JJ (I think) GZ34. A different story with the EL34s, where a set of Mullards returned 0.04% THD, compared with the JJs 0.1%.
 
I couldn't hear any difference between a Mullard and Harma GZ34.

The Mullard is reputed to be more reliable (especially if the value of the first 32uF cap has been bumped up) and that may well be true but the price of NOS Mullards is so high now that I don't think it makes economic sense. If you buy a used Mullard GZ34 you're taking a gamble, which might pay off or it might not.
 
Thank you all for your invaluable help so far. Valves are a new area for me and I really enjoying bringing some examples back to life. :)

I shall do the diode mod for the GZ34 this morning, soak test of an hour or so on the bench and then I shall move it to the system upstairs for a listen.

Exciting...
 
Well, it works, who've thought it with my lack of skill :)

PXL_20220420_163443973 by Garf Arf, on Flickr

I do adore the colour and from this distance one can't quite see all the bumps and scratches of its 49 year life.

My OCD got the better of me and I installed a set of Hirschmann speaker connections, no fuss, low profile connections that can accommodate the Deltron banana plugs completely.
PXL_20220420_162553093 by Garf Arf, on Flickr

It has, on the whole cleaned up quite well...

From this
2022-03-23_06-39-55 by Garf Arf, on Flickr
to this...

PXL_20220420_161333133 by Garf Arf, on Flickr

PXL_20220420_161308832 by Garf Arf, on Flickr
2022-04-20_07-33-32 by Garf Arf, on Flickr

PXL_20220420_162117009 by Garf Arf, on Flickr

For spotters amongst you, those are Sovtek 12AX7LPS Long Plates :)

I've only managed a couple of tracks with it so far, hopefully later I can spend some quality time with it. So far, the sq has been very good with not a hint of hum in the speakers, even with my ear against them (well as close as I dare put my ear against 57s!).

Heat wise, the mains transformer does get a little hot. Nothing unbearable, but warmer than the Quad II's mains transformer gets.
 
As a bit of a postscript/happy ending. I texted Stan, the man I bought the amp from originally, with a link to the Stereo 20 Filckr album so he could see what I had done to his old amplifier. He texted this back to me just...

Hi Simon
I'm absolutely stunned
You have been busy as well. A first class job.
I'm enjoying the early evening light here in Cornwall and talking to the family about how I was able to keep it with me after so many years and house moves.
So good to see it restored
All the best
Stan

Just lovely....
 
chiily said:
More pictures of the EL84s and the ECC83
PXL_20220417_174354891~2 by Garf Arf, on Flickr
PXL_20220417_174327430~2 by Garf Arf, on Flickr
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I've done a bit of digging on how the manufacture of these EL84s might be. The most noticeable feature is the U shaped "chimney". Most other EL84's have two separate, parallel plates. I could only find two manufactures who's valves had this characteristic U shape. The first is 6BQ5 Lindal Japan and the EL84 Brimar (pictures in the links).

The winner I think is the Lindal 6BQ5, mainly because in the linked picture is has the same 6BQ5 marking, with a number after it, as the Pinnacle ones have.

2022-04-17_04-24-11 by Garf Arf, on Flickr
 
chiily said:
16R it is then, ta :)

I do like these Switchcraft right angle phonos, and the wonderful glow...
2022-04-21_09-07-33 by Garf Arf, on Flickr

I'm not finding the amp's sensitivity a problem when using a miniDSP as a pre-amp/volume control. As been said before the Leak sounds more "modern" that the Quad IIs.
Click to expand...

Does anyone sell cables ready-made with these RCAs? Ideally with straight RCAs at the other end.

regards

Kevin
 
kevinrt said:
Does anyone sell cables ready-made with these RCAs? Ideally with straight RCAs at the other end.

regards

Kevin
Click to expand...

The ones in the picture are built from Switchcraft RCAs (3502-A and 3502-RA) and Mogami 2549 cable. I've never seen them ready made, but they are not hard to make. If you want I could source some parts and build you a pair.

I find the Switchcraft connectors really robust, straightforward and no nonsense. The 2549 was a length of cable I had hanging around, I bought it from Redco years ago when I couldn't find Mogami cable in the UK being sold by the metre.
 
chiily said:
The ones in the picture are built from Switchcraft RCAs (3502-A and 3502-RA) and Mogami 2549 cable. I've never seen them ready made, but they are not hard to make. If you want I could source some parts and build you a pair.

I find the Switchcraft connectors really robust, straightforward and no nonsense. The 2549 was a length of cable I had hanging around, I bought it from Redco years ago when I couldn't find Mogami cable in the UK being sold by the metre.
Click to expand...

I assume they are soldered connections. That’s where I lack skills. I’ve got the soldering iron etc, but whenever I try I’m never happy with the results.

regards

Kevin
 
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