Leak TL12+ Rebuild

Radford Revival

Wammer
Wammer
Mar 7, 2012
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Will
Hi everyone,

I am in the process of restoring a nice pair of Leak TL12+ amplifiers. I've taken pictures of my work so far in case anyone is interested.

Here they are, in fairly untouched original condition. There were a couple of bodges underneath but luckily nobody has butchered the bodywork.

SAM_2621.jpg


Quite nice looking amps with valves in.

SAM_2623.jpg


Underneath

SAM_2624.jpg


Rear of one

SAM_2627.jpg


Close ups of underneath

SAM_2633.jpg


SAM_2634.jpg


 
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Radford Revival

Wammer
Wammer
Mar 7, 2012
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Will
Fast forward a bit and here we have all the passives replaced :party:

SAM_2639.jpg


As you may be able to see in the previous pictures, the original smoothing caps were a bit knackered. As they are part of the amplifier's "look" it was necessary to keep the original cans. Luckily modern electrolytics are physically smaller so it was possible to strip the original capacitor out (a messy job :nup: ) and fit a new one in.

A bit of creativity with a saw, large pliers and potting compound leaves us with this (cable ties for keeping them central long since removed!):

SAM_2641.jpg


 

Valvebloke

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Nice work Will :^ , and nice amps. People sometimes describe these as being like a Stereo 20 split into two monoblock halves. But they're not really. The Stereo 20 has an all-triode front end whereas the TL/12+ has an EF86 feeding an ECC81. This pentode/double triode arrangement echoes the TL/12 Point One circuit which, of course, the TL/12+ replaced.

VB

 

Radford Revival

Wammer
Wammer
Mar 7, 2012
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Will
Nice work Will :^ , and nice amps. People sometimes describe these as being like a Stereo 20 split into two monoblock halves. But they're not really. The Stereo 20 has an all-triode front end whereas the TL/12+ has an EF86 feeding an ECC81. This pentode/double triode arrangement echoes the TL/12 Point One circuit which, of course, the TL/12+ replaced.VB
Interestingly the phase splitter circuit uses the same resistor values / topology as the ECC83 splitter in the Stereo 20. Not having drawn any load lines I suppose it's just a happy coincidence the the same values bias both valves correctly.

 

pure sound

Wammer
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Nice neat work again :^ Did these have the same 'resistor as fuse' arrangement as the ST20? Can't tell from the pics. Presumably these were originally sold as Mono amps (with mono pre) & pre-date the ST20.

 

Radford Revival

Wammer
Wammer
Mar 7, 2012
231
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Will
Nice neat work again :^ Did these have the same 'resistor as fuse' arrangement as the ST20? Can't tell from the pics. Presumably these were originally sold as Mono amps (with mono pre) & pre-date the ST20.
Hi Guy,

I hope to work a fuseholder into them eventually, as far as I've fiddled with I have yet to find a convenient place. Due to the constraints of where things fit I may just have to fuse the output stage by itself, but of course that's the most potentially destructive bit by far.

 

Valvebloke

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Interestingly the phase splitter circuit uses the same resistor values / topology as the ECC83 splitter in the Stereo 20. Not having drawn any load lines I suppose it's just a happy coincidence the the same values bias both valves correctly.
In that circuit the ECC81 runs at very low current - only about a milliamp per triode. This drops the gm and raises the anode resistance to values which are much closer to those of the ECC83. The mu's still differ by nearly a factor of two of course. But what's a factor of two between friends ...

VB

 

Radford Revival

Wammer
Wammer
Mar 7, 2012
231
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South West
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Will
Had some bits made! Mode pictures coming soon. We will be eventually offering these bits for sale for your Leaks. We will also be producing Stereo 20 bits.

The black pieces are to fit Cliff binding posts, and the rectangular black piece is to fit a toggle mains switch in place of the external mains supplies which no one in their right mind would use anyway! These will also fit on Stereo 20s. They were made so the original plastic bits can be kept aside if one wants to return to original condition. They are not yet fitted in the pictures below.

SAM_4567.jpg


SAM_4570.jpg


SAM_4572.jpg


 

robin

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like the base plate, good idea, will be after one for my 20

 

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