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Mike's Stereo 20 refurbishment thread.

If I really wanted to use two I’d be far more tempted to vertically bi-amp assuming bi-wired speakers, that way any amp mismatching (non-identical transformers or whatever) isn’t quite so crazy obvious on the stereo image etc. Active would be an option too. Time to design a valve crossover?!
 
Tony L said:
If I really wanted to use two I’d be far more tempted to vertically bi-amp assuming bi-wired speakers, that way any amp mismatching (non-identical transformers or whatever) isn’t quite so crazy obvious on the stereo image etc. Active would be an option too. Time to design a valve crossover?!
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Yeah bi amping and active also options... and a valve crossover is no problem other than it would be vastly more expensive than one using op amps and for obvious reasons... Well, no problem beyond the usual very difficult problem of making an active crossover IE there's so much more to it, usually, than just making a perfectly flat crossover that crosses over at say 2KHz! Just look at all the extra things the crossover does in say LS3/5A's to give a genuinely flat response once driver resonances etc have been accounted for!

The need to match channels is nothing to do with stereo image BTW... it's the L & R channels on each chassis that need to be a decent match so that (to exaggerate a bit) if L chan gives 4V and R chan gives 5V for a mono input then R chan is not trying to drive 1V into left chan.
 
Arkless Electronics said:
The need to match channels is nothing to do with stereo image BTW... it's the L & R channels on each chassis that need to be a decent match so that (to exaggerate a bit) if L chan gives 4V and R chan gives 5V for a mono input then R chan is not trying to drive 1V into left chan.
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I understand that, I’m just not 100% sure Leak used the same supplier for transformers etc, and the last thing one would want is a slightly mismatched stereo pair of amps. I’m certainly being exceptionally picky in my search to find another TL12+ as I want one absolutely identical in every way to the one I have and don’t really care if it takes years to find!
 
My second ST20 is now done.

P1110238 by Michael Pickwell, on Flickr

It has been rebuilt to pretty much exactly the same spec as my first:

  • Takman REX resistors
  • Russian K40Y-9 paper in oil capacitors
  • Sprague Atom 50uF axial electrolytics
  • F&T reservoir caps

I fitted the same spark suppressor and used the same speaker binding posts.

P1110242 by Michael Pickwell, on Flickr

P1110243 by Michael Pickwell, on Flickr

P1110244 by Michael Pickwell, on Flickr

There are a few small differences though:

  • C9 (200pF) on my first amp are polystyrene but on the second amp they are mica. I chose to leave the orignals in place.
  • I couldn't find any 1000pF K40Y-9 for C1 like I used in my first amp so instead I used some polystyrenes.
  • I have increased the big electro cap at C10+11 to 50uF+50uF (but left C12+13 at 32uF) and I have also done the same to my first amp.
 
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Tony L said:
Beautiful job, looks great. How does it sound?
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Thanks Tony, it was much quicker the second time around since I knew exactly what parts I wanted.

I used the same VW Sand Metallic paint as on the first unit and I'm still not 100% satisfied with the colour match. At some point I'll get around to having a colour-matched aerosol mixed and do the big electros on both amps again.

I've only had a chance to listen via my stunt speakers so far and haven't yet tried it on the Tannoys.
 
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The VW paint is close enough for me as there is a fair bit of difference between the original chassis, which is beautifully done, and the transformer covers and original capacitors, which are far less so. To my eyes, which admittedly are not the best with regard to colour, my sprayed F&T are no more ‘different’ to the chassis colour than the originals were, albeit in a very slightly different way.

PS Looking at your picture I’d argue your caps match the chassis far better than the transformer covers!
 
Dear Mike,

This thread has brought a big smile here!

So nice to read about such superb work on worthy classical amplifiers.

My efforts with the Troughline are as nought in comparison, though the work is just as fine. What makes yours so much more interesting is that you had complete control over what was done, and done so beautifully.

It makes me think that one day, if we have better days in the future, I would love to get a TL 12.1 or TL 12 Plus, and really round out my own system between my Troughline and the ESL.

These classics bring pleasure that seems much longer lived than even the newest modern pieces, and they seem to perform amazingly well - the more so when you think they were this good most of a lifetime ago!

It is now more than ten years ago since I started to restore the Carlton, and it is still wonderful. A blemish here or there on a classic seems to matter not a bit unlike a scratch on a black or silver aluminium case!

Best wishes from George
 
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George J said:
Dear Mike,

This thread has brought a big smile here!

So nice to read about such superb work on worthy classical amplifiers.

My efforts with the Troughline are as nought in comparison, though the work is just a fine. What makes yours so much more interesting is that you had complete control over what was done, and done so beautifully.

It makes me think that one day, if we have better days in the future, I would love to get a TL 12.1 or TL 12 Plus, and really round out my own system between my Troughline and the ESL.

These classics bring pleasure that seems much longer lived than even the newest modern pieces, and they seem to perform amazingly well - the more so when you think they were this good most of a lifetime ago!

It is now more than ten years ago since I started to restore the Carlton, and it is still wonderful. A blemish here or there on a classic seems to matter not a bit unlike a scratch on a black or silver aluminium case!

Best wishes from George
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Thank you for the lovely message George.

I still find it hard to believe that a 57 year old amp sounds so good.

I think the truth is that good kit is good kit regardless of age. My ST20 is 57 years old, my speakers are 40 years old, my turntable 40+ and even my favourite CD player is 30 years old. All of this kit has been selected on merit and if it didn't still sound superb (even by modern standards) it wouldn't be in my main system.

Nice to hear about your Carlton. I'm a keen cyclist myself and have owned and restored a couple of Cartlons in the past.

These days I make my own fillet brazed frames, usually from Reynolds 853.
 
You did say at least two @Tony L

Tony L said:
Excellent, everyone should have at least two!
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P1110324 by Michael Pickwell, on Flickr

The one furthest from the camera is the latest rebuild and is actually my first 'customer commission' for a rebuild. It's all finished and I'm sat listening to it now. :)

It has a few subtle differences from my two, the most obvious being that it doesn't have the usual fuse carrier on the back. Instead the fuse is integrated into the voltage selector plug that inserts into the mains transformer.

I'm pretty sure this one was all original when it came to me and interestingly many of the parts were slightly different. The two big eletrolytics appear to be of different manufacture, the resistors were a yellowish colour (rather than brown) and some of the small electrolytics were a different brand etc.
 
Cool! Did you try testing any of the original Plessey Metalpack caps? Japanese Leak fans try to keep them where possible. I have a full set in my likely unused grey Stereo 20, but I’ve no plans to restore that or power it up (I just view it as an investment that I’ll just move on at some point, really I only wanted the tube-set and box for mine!).
 
The two big bronze coloured electro's in this latest one were in good shape both visually and electrically and could probably have been safely reused but I fitted new F&T caps anyway to ensure trouble free longevity for the owner.

I haven't measured the smaller value capacitors but I did save them in a bag for the owner in case he wants to sell them on ebay to some crazy Japanese audiophile.

I just wouldn't feel happy running 60 year old electrolytics or ancient way out of spec carbon comp resistors. It has to be 'right' for me which means fitting new quality parts.
 
Does anyone know a source of double solder tags that are a good match for those used on a Stereo 20?

I'm doing another ST20 rebuild and a few of the originals are broken. I can manage without but it would be nice to replace the damaged ones.
 
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