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Acquired a nice ST 20 a little while back, and just bagged a passive pre. Is there any consensus / preference for interconnects between the pre and the Leak?

(and yes, I know I'm potentially opening up a whole can of worms here)

As a rule of thumb keep them as short as possible and as low capacitance as possible. Not a huge issue with the Leak as its input impedance is very high at 1mOhm, but I'd still stick to sensible low capacitance cable. Van den Hul cable tends to be very low capacitance and is good with passive pres IME.
 
As a rule of thumb keep them as short as possible and as low capacitance as possible. Not a huge issue with the Leak as its input impedance is very high at 1mOhm, but I'd still stick to sensible low capacitance cable. Van den Hul cable tends to be very low capacitance and is good with passive pres IME.

Thanks Tony, appreciate your input!
 
I now have two! The local auction came good again today...

37354182864_f34a372988_b.jpg


A rather tidy 1965 grey Stereo 20 complete with box, manual and leads. I paid way more than I was hoping as there was one other punter in the room that obviously knew what it was and drove it right up. Without him I’d have had it for £30, with I ended up payng £473 including auction fees, which was very, very close to my own red-line of £500.

37354182894_0a3398ef38_b.jpg


The reason I paid quite a hefty wedge for something I already own is it looks totally stock, maybe even NOS even though it has a couple of minor cosmetic issues (one scratch and some slight discolouration where the octal cable was coiled on top which won’t come off). The reason I suspect it may be NOS is the tube set is certainly original, all the date codes match, the three Mullard ECC83s and EL84s being a proper matched trio/quad when it comes to date codes and batch numbers, and more significantly there is not even the slightest hint of any heat marking on the circuit board around the green ‘drop’ resistor. I’ve never seen a Stereo 20 this clean underneath.

Leak Stereo 20 prices seem to be rocketing at the moment, some good examples going over £1k, so really I bought this as an investment. I’m just going to keep it as-is as people seem to pay the most money for really good unrestored originals so they can choose their own rebuild strategy. I can certainly understand this as I ended up ripping out the previous rebuild of my bronze one and doing it with what I view as more sympathetic components. I’ll try out some of these lovely tubes though!

PS Anyone know if it is possible to check the transformers with a multimeter without powering it up (which I obviously can’t do)? I have no reason to suspect any issues, but it would be nice to know they were ok.
 
Are you the same Tony L who keeps saying he has too much kit?......

Looks very clean indeed, probably hardly used, pretty good investment I should think.
 
Are you the same Tony L who keeps saying he has too much kit?......

Looks very clean indeed, probably hardly used, pretty good investment I should think.

Ha, indeed! Not too hard to stash a box though, especially if it may potentially double the investment! I know where I could get a Wharfdale SFB3 for not a lot of cash, but I’ve nowhere to put that!

PS Here’s another underneath shot, I’ve never seen any Stereo 20 with no heat marking at all under the green resistor!

26287310489_2f1b0a8cf1_b.jpg
 
Looks NOS. I've never seen one that clean. Not even a hint of wax leaking from the transformers. It's a pity it will need a complete rebuild to be any use....

You can only do basic tests on the transformers with a multimeter. ie test they are not open circuit or shorting to ground. You could remove the GZ34 and power it up and test the AC voltages from the mains TX of course.
 
WOW! That's amazing! ST20 is truly a great amp, far better than most would imagine. £473 I don't think that's a high price these days, they were going for £300 back in the 90s (and that's for normal worn types). Nice!



I now have two! The local auction came good again today...

37354182864_f34a372988_b.jpg


A rather tidy 1965 grey Stereo 20 complete with box, manual and leads. I paid way more than I was hoping as there was one other punter in the room that obviously knew what it was and drove it right up. Without him I’d have had it for £30, with I ended up payng £473 including auction fees, which was very, very close to my own red-line of £500.

37354182894_0a3398ef38_b.jpg


The reason I paid quite a hefty wedge for something I already own is it looks totally stock, maybe even NOS even though it has a couple of minor cosmetic issues (one scratch and some slight discolouration where the octal cable was coiled on top which won’t come off). The reason I suspect it may be NOS is the tube set is certainly original, all the date codes match, the three Mullard ECC83s and EL84s being a proper matched trio/quad when it comes to date codes and batch numbers, and more significantly there is not even the slightest hint of any heat marking on the circuit board around the green ‘drop’ resistor. I’ve never seen a Stereo 20 this clean underneath.

Leak Stereo 20 prices seem to be rocketing at the moment, some good examples going over £1k, so really I bought this as an investment. I’m just going to keep it as-is as people seem to pay the most money for really good unrestored originals so they can choose their own rebuild strategy. I can certainly understand this as I ended up ripping out the previous rebuild of my bronze one and doing it with what I view as more sympathetic components. I’ll try out some of these lovely tubes though!

PS Anyone know if it is possible to check the transformers with a multimeter without powering it up (which I obviously can’t do)? I have no reason to suspect any issues, but it would be nice to know they were ok.
 
Well the 1965 ‘four notch’ Blackburn Mullard GZ34 rectifier certainly works! I’ll try the ECC83s and EL84s later. I’m rather curious to hear the Mullard EL84s assuming they are ok as I’ve never compared them to the Russian 6P14P-EV I run in mine. In a way I hope they aren’t hugely better as they are a hard to find and therefore expensive tube these days. I’ve been running similar period Mullard ECC83s and a slightly later (‘seven notch’) GZ34 in my Stereo 20 for a good while now, just chickening out of finding a set of Mullard EL84s.
 
...now got the full tube-set running in ‘my’ Stereo 20 and they are certainly fine. I stuck the EL84s in before taking a break for food, now the three ECC83s. FWIW I don’t feel the Mullard 84s are better than the Russian 6P14P-EV, just slightly different; a little more airy and 3d in the treble, but a little less punchy and dynamic too. Swings and roundabouts really, both being really nice. I’d not personally pay 3x or more the price for NOS Mullards, whereas I would with the ECC83s and GZ34, and have done!

The more I look at this amp the more I suspect it really is NOS. Things like the speaker terminal screws just look mint with no indication anyone has ever taken a screwdriver to them, then as commented abve the total lack of heat evidence. The negative being it does have some cosmetic blemishes through bad storage, the most annoying being the marking to the top painted area between the two rows of tubes where the paint has I think reacted to the octal lead being coiled there, so its NOS, but certainly not mint! You’d not notice it in use though, it still looks nice and the sides and back are all very clean and tidy. (I uploaded the pics straight from my iPhone with no post-processing and they are rather flattering and make ut look far too dark, it is the charcoal grey one would expect).

The potential NOS aspect is obviously very good news for the valves. This is obviously an collectable/expensive set of tubes and very likely worth what I paid for the amp. All 1964 yellow-print Blackburn Mullards with matching date codes on the trio of 83s and quad of 84s. I’ll run them for a few hours tonight, which may actually do them some good as it should get any rogue particles that need sticking to the getter stuck to the getter, and then I’ll just put everything back in its box and sit on it a few years until it is time to move it on!
 
I have a circa 1967 Stereo 20 which used to belong to my Uncle, that I’ll be collecting on Sunday. A friend of mine collected it for me from Cornwall yesterday and took a few snaps for me for me to look at it in meantime. Unfortunately the unit has evidently been ‘got at’ by a repairer in the past, and there’s quite a burned area on the paxolin board, fortunately the mains transformer is fine. The ‘magic’ 3 watter has been replaced by a 5W RS type, obviously this repair guy didn’t quite have the knowledge to restore with the correct 3 watt item, if indeed that resistor actually needed replacing in the first place! He’s also replaced *just* the one 50uF cathode bypass nearest that resistor, but left the other three stock! All four 270R cathode resistors have been changed too by the look of it. He’s also changed all four 0.22uF PIOs to Mullard mustard types. Everything else is stock. Reasonably neat work but I’ll be stripping the whole lot down and rebuilding with as close to period correct parts as I can (modern TE CFR 1W and 2W carbon films, Russian PIOs etc). I’ll save all that for a fresh thread.

33714955078_a140f12c7c_o_d.jpg


Two questions as I’d like to order these today if possible:

1) Would the following be a suitable replacement for the original 100 ohms 3 watt item, baring in mind it needs to still act as a safety resistor and ‘desolder itself’ if need-be like the original. Or are the properties of the original in regards to how much heat it takes before doing so an unknown?

https://uk.rs-online.com/web/p/through-hole-fixed-resistors/1393383/

2) I’d like to fit a suitably rated (and if possible, vintage toggle style) on/off switch into the switch cable hole at the rear of the amplifier. Has anybody already done this and has a part number?

Cheers!
 
Reasonably neat work but I’ll be stripping the whole lot down and rebuilding with as close to period correct parts as I can (modern TE CFR 1W and 2W carbon films, Russian PIOs etc).

Oh dear... Those are nowhere near close to period parts...
 
Would the following be a suitable replacement for the original 100 ohms 3 watt item, baring in mind it needs to still act as a safety resistor and ‘desolder itself’ if need-be like the original. Or are the properties of the original in regards to how much heat it takes before doing so an unknown?

By the time of the grey chassis (i.e. both later output and lower voltage mains transformer) Leak seemed to have abandoned the ‘drop’ resistor as a safety feature. If you look at my NOS example you’ll notice the eyelets the resistor is mounted through haven’t been cut, i.e. it couldn’t ‘drop’ even if it got hot enough to melt the solder. I can only assume Leak thought they had fixed the issue with the various component changes.

PS Being more than somewhat obsessive the thing I don’t like in your picture is it looks like the person who did the rebuild/bodge has flattened some of the tags to make the shorter components such as the ‘mustard’ caps fit. These tags are not especially strong to start with and one of mine actually broke off (one of the four really big red resistors). Not a huge issue in this case as they are double-ended and I just took it to the other side. I suspect in my case it failed due to the earlier rebuild (which was far less neat than my work) weakening it. I’d be very wary of trying to bend the flattened ones back anyhow as it wouldn’t take much to crack them. Other than that I’m sure you can achieve a great restoration! What does the top side look like?
 
Oh dear... Those are nowhere near close to period parts...

Close = retaining similar materials, to retain a similar 'voicing', with more modern reliability. I could go full-on retro with carbon composite resistors instead of carbon films, and NOS TCCs, but I want something that will last without parts drifting off spec in a year or two or leaking caps.

Thank you.
 
By the time of the grey chassis (i.e. both later output and lower voltage mains transformer) Leak seemed to have abandoned the ‘drop’ resistor as a safety feature. If you look at my NOS example you’ll notice the eyelets the resistor is mounted through haven’t been cut, i.e. it couldn’t ‘drop’ even if it got hot enough to do so. I can only assume Leak thought they had fixed the issue with the various component changes.

PS Being more than somewhat obsessive the thing I don’t like in your picture is it looks like the person who did the rebuild/bodge has flattened some of the tags to make the shorter components such as the ‘mustard’ caps fit. These tags are not especially strong to start with and one of mine actually broke off (one of the four really big red resistors). Not a huge issue in this case as they are double-ended and I just took it to the other side. I suspect in my case it failed due to the earlier rebuild (which was far less neat than my work) weakening it. I’d be very wary of trying to bend the flattened ones back anyhow as it wouldn’t take much to crack them. Other than that I’m sure you can achieve a great restoration! What does the top side look like?

Yes I noticed the bent tags too. Seeing this work has tempered my enthusiasm just a tad, but having zoomed into some other photos my friend took it looks like (touch wood) no tags are actually broken. I intend to carefully desolder all the components, clean it all up, then very gently bend each tag back. Have had experience of this with the various Quad IIs I've worked on and they're usually OK if one goes very slowly indeed. The top side is covered in a thick patina of dust, and one of the transformers seems to be at a bit of an angle, so it'll likely need a damn good clean. Going to go for a full dismantling of the unit like Snowman-Al's work earlier in this thread and will wash the chassis in warm water and a little fairy liquid. Hoping it'll all clean up OK. Its been housed within a cabinet since 1967 so touch wood it's just decades of dust and there won't be too many marks or scratches etc.
 
I know just how good you are at this stuff so will be very interested to follow your progress. It really is worth the effort IMO, a superb sounding amplifier when sympathetically restored. In hindsight I wish I’d completely disembowelled mine both to clean it properly (there will be all manner of crap on top of the board) and I’m sure reworking will be way easier with the board out of the unit. It also presents the opportunity to crack open the transformers to clean them better. The sockets at the top are likely very crusty.

For switches google Classique Sounds Leak and have a look at images. They fit something that looks like it is off an old guitar amp. No idea if they need to drill the hole out. I turn all my kit on/off at my switched mains block so didn’t bother replacing the piece of ill-spec’d crap that had been my noise issue all along! No power switch on the 303, so I’m well used to it.
 
You can still relatively easily do that though. All the valve bases unscrew easily, and I think you'd then just have to desolder the can caps, and all connections to the transformers, then the board would just lift out? (easier said than done I know as I haven't done it yet!). Might be worth doing it once to get rid of that last restoration niggle though, and as you say to clean the transformers.

I'll go do a Google search for their images now - cheers!
 


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