Sacrilege or sensible...

[rabski]

One of the last of the Leak garage collection. I'm usually quite strong on 'cosmetic originality within reason', however, this was a sad Stereo 20 that had already been hacked about by someone in the past, so there was little point in trying. As I'm possibly going to keep this one, it's also turned into an experiment to see just how far it can go.

The most obvious change from standard is the additional lump of a choke on the top. That's because the power supply has had somewhat of a rethink. This is just more in line with the TL12 Plus circuit, though with some more tweaks. The other main cosmetic difference is decent quality ceramic valve sockets, and rather than self-tapping screws, everything is hex bolts. The chassis and all the transformer covers were sand blasted and powder coated. It's not perfect, because they were really corroded and pitted. Attractive enough though.

Under bonnet shots tomorrow, when it's finished. Pretty much original in terms of circuit, though with a few small niceties. The main change is component specs and layout. This has ended up a bit insane, with Audio Note coupling capacitors, a mix of Audio Note and Kiwame resistors and an awful lot of Duelund and Neotech wire. The wiring layout is also very different, with a lot of care over keeping signals clean and single-point star grounding. An awful lot of time involved, but hopefully it will all work, then it will be fun to see what it sounds like...

 

[pmcuk]

I fitted long top plates on either side where the sockets are so as to get 10 nine pin sockets, 5 a side. Didn't drill anything so it's reversible. I then fitted 8 of 6S4 triode output tubes, no feedback. This took up all the 6.3v supply so the input tubes run off the 5V supply. I can use 4BQ7 or 5BK7 for instance as voltage amp/concertina. No rectifier tube, the B+ comes via 1200V Schottky diodes. I have a couple of 10H 100mA chokes under the bonnet, wired in parallel. I think this is quite a sensible design (Leakies choke at this point....). Looks OK too in gold. I wanted the top to look fairly sparse, and in fact it's more symmetrical than the original.

 

[Jazid]

Go Richard! Mr HJL never put a foot wrong, and nor will you. But champagne please, not black.

 

[rabski]

Go Richard! Mr HJL never put a foot wrong, and nor will you. But champagne please, not black.

It's actually metallic grey, and very close to the original. Not that I'm overly fussed with this one.

There are a nice pair of Edcor OPTs in the collection, which are destined to be a 'start from scratch' EL84 PP, so I can butcher the circuit for that one. Not everyone's taste sonically, I know, but I like the TL12/Stereo 20 sound. It's slightly 'cleaner' with modern close tolerance bits though, especially in the NFB circuit. As always, decent resistors and capacitors make a subtle difference when there are enough of them.

 

[rabski]

Finished article. Now running in the system and sounding very decent. All the caps are brand new, so I expect it to loosen up and get more expansive sounding over a few hours. May well keep it. Quite fun to have an alternative to the others

 

[DUVET]

Nice tidy work Rich . Flip some of these over and its like spaghetti junction on steroids .

 

[MotherSky]

That looks extremely smart - very nice work. If those AN caps are anything like Black Gates you're going to have to be very patient to hear it at its best - MH

 

[rabski]

Nice tidy work Rich . Flip some of these over and its like spaghetti junction on steroids .

Touch of OCD mate. Drives me mad to see it all messy, though actually making it tidy can result in noise sometimes.

 

[rabski]

That looks extremely smart - very nice work. If those AN caps are anything like Black Gates you're going to have to be very patient to hear it at its best - MH

They are.

I've got large AN Copper in the preamp and I reckon it took 100 plus hours before they stopped changing substantially.

 

[Jules_S]

That looks like an excellent job done, Richard, very smart. I understand the desire to keep things original sometimes, like restoring a classic car back to how it was when it rolled out of the factory. But then sometimes there's those "barn find" jobs that are just too far gone, and I don't see the harm in doing a modernisation and coming up with something a bit unique. Saves it from the scrapheap, where it might otherwise find itself

Looks very smart in that grey finish, and although I'm personally not that keen on the whole "exposed" look of the transformers that most vintage gear has (and the lack of symmetry in the original placement of the valves sets my OCD off ), I reckon most people would be happy to have something like that in their equipment rack. And no doubt it sounds superb.

 

[zeta4]

Nice work as usual. Are you doing something sneaky with the OPT? There doesnt seem to be
enough wires connected to it though it could be the pic.

 

[rabski]

Nice work as usual. Are you doing something sneaky with the OPT? There doesnt seem to be
enough wires connected to it though it could be the pic.

It's the pic. I've kept it in UL configuration, exactly as per original. All the valve to OPT wires are Duelund, so hard to see in the picture. I did try it as both triode and pentode. Triode is pleasant, but not enough power and clips very early. Pentode seems to take away the fun factor. Overall, all I've done with this is stick to the original design (Mr Leak knew what he was doing) but build it without the compromises imposed by component specs and costs.

There is a final one in the pile that has also been attacked in the past. Plan C is possibly to rework it exactly the same as 'this' one, then try running them as paralleled monos. Possibly a bridge too far though. I really need to put workshop time aside to concentrate on other stuff.

 

[Psilonaught]

Those AN caps look like silver foil, but I assume are not? New old stock copper foil?

 

[rabski]

Those AN caps look like silver foil, but I assume are not? New old stock copper foil?

You assume right. They're the tin foil/mylar in oil ones. Good though it is, and excellent though they are, spending over three and a half grand on silver in oil capacitors would be a step too far I believe

 

[MVJ]

They are.

I've got large AN Copper in the preamp and I reckon it took 100 plus hours before they stopped changing substantially.

Thats only five/six days Richard get yourself a 24 pack of Redbull mate & go for it