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Old 2nd Dec 2017, 10:57 pm   #1
vishalk
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Default Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed.

Hi All

Please see the attached pictures or links below for detailed pictures.

This is a lengthy post so have a cup of tea and bare (bear) with me please!

It seems I got bitten by the valve amplifier bug, especially for vintage British amplifiers.

I don't know what came over me but I had to have these amplifiers in my collection (much to my wife’s dismay).

I wanted to find unmolested examples with hope that some of the components may still be OK and that I may be able to salvage some parts and keep to the original design and sound.

My personal ambition is to refurbish them and learn how to fix, repair and understand valve technology, which is becoming a rare art.

I put myself on a 4 day course with vyse amps:

http://vyseamps.com/training-courses.html

A very nice gentleman named Barry runs them, he has been very kind and accommodating to suit the course based around this project!

I managed to find an out of print book “Firsts In high fidelity” The Products and History of H. J. Leak by Stephen Spicer (really lucky find) This book will hopefully inspire me and give me some much needed information.

I’ve been scouring the internet and there is a great deal of information out there, some of it confusing and misleading.

This is where you guys come in, I’m sure there are many of you on here who have experience and knowledge to give me ideas and guidance on the best course of action for these wonderful amplifiers.

So lets get started I have so many questions!

Pictures of Leak ST20 and Preamp

https://i.imgur.com/I9JacRX.jpg
https://i.imgur.com/KFGGNfd.jpg
https://i.imgur.com/8ocIMOd.jpg
https://i.imgur.com/6Mh1OvR.jpg
https://i.imgur.com/dxRBuxI.jpg

Internals of ST20 and Preamp

https://i.imgur.com/Ad0w8hu.jpg
https://i.imgur.com/HK48oGk.jpg
https://i.imgur.com/JiKjWJJ.jpg
https://i.imgur.com/flfKwP3.jpg
https://i.imgur.com/xnAt7TB.jpg
https://i.imgur.com/uXXUoyd.jpg
https://i.imgur.com/2Qc1PMv.jpg

Pics of the TL12 +

https://i.imgur.com/uDZgFdI.jpg
https://i.imgur.com/OzyG018.jpg
https://i.imgur.com/grdOzhn.jpg
https://i.imgur.com/0GdKQUR.jpg
https://i.imgur.com/sIjXFF0.jpg
https://i.imgur.com/eDpOJAm.jpg
https://i.imgur.com/sv7c6WK.jpg
https://i.imgur.com/FA2wGSw.jpg
https://i.imgur.com/qK9FHfk.jpg
https://i.imgur.com/2n6VrYB.jpg
https://i.imgur.com/rTSMxex.jpg

Last edited by vishalk; 2nd Dec 2017 at 10:59 pm. Reason: added pictures
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Old 2nd Dec 2017, 11:19 pm   #2
vishalk
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

I'm trying to show the pictures on this thread but can only seem to give links, if anyone can tell me how to show the pictures on the actual thread that would be most helpful!

So the ST20 is in original condition, it was kept in an attic and not used for 20 years. It comes with the preamp (which I read is not really the best) and lots of replacement valves by Mullard and Tungsram.

Now it looks all healthy and I am tempted to plug it in and see if it works, but again I've read and been told this isn't wise because most certainly some of the components would have perished due to age (i.e the capacitors). My guess is all the components will need changing.

So I would like to know what other members suggest in terms of replacement parts and any necessary mods they see fit.

I would like to keep it as British as I can, what I mean by that is use UK made parts such as PIO (paper in oil capacitors) or some other form of Oil based capacitors:

http://www.audionote.co.uk/comp/cap_paper.shtml

I would like good quality components in there, the right components to get the best out of these amps. I probably will change the power connectors to IEC and if I can add a safety fuses where necessary.

Another I'm trying to get my head around is the input sensitivity, I would like to use this amp with modern type equipment i.e Ipad, CD player etc. I have two preamps one modern type being a LFD/Mistral and a Marantz 7m7 valve type. So would I need to modify the amplifier to suit? I've read about modifying it to run triode output not sure if thats worth while.

I guess I could get it back to original working condition and then later try some modifications later on.
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Old 2nd Dec 2017, 11:22 pm   #3
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

My first rule when servicing these types of amplifier is to change the coupling caps to the output valves. I also replace as a matter of course the grid leak resistors and if they are out of spec the phase splitters anode load resistors. This is non negotiable. SERIOUS DAMAGE CAN OCCUR IF THESE COMPONENTS ARE NOT REPLACED.

In fact I go further with this, I replace all old paper /wax, Hunts mouldseals and anything that looks suspicious.

I use vishay 2W metal resistors rated at 500V and Vishay axial capacitors rated at either 400V or 630V polyester types and Vishay electrolytic capacitors.

They are fairly simple amplifiers that are easily serviced, but do sound good when working.
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Old 2nd Dec 2017, 11:30 pm   #4
vishalk
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

My worry is one of the TL12 plus amps had all the valves blown (see pictures where the tops of the valves are all white) pretty obvious something went wrong! I am hoping the transformers and output trannies have not been damaged because of this. A lovely member on here frankmcvey told me Ed Dinning can help with this if it's a problem (how would I test for this though)


Just like the ST20 I plan to get these singing again, although on these amps I will completely refurbish them. I will even go as far as redoing the chassis and having them repainted.

I am open to suggestions on ways to improve these amps, in terms of components, adding chokes (heard you can do this to the ST20 aswell) etc.

The TL12 plus are really for me to learn on and try things, the ST20 I really want to go original.

So please send me links, ideas, things you have all done, components that you recommend and anything else that will get me going!

I am really excited to get this going and see where it goes ( hopefully not electrocuted)
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Old 2nd Dec 2017, 11:50 pm   #5
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Quote:
Originally Posted by Michael Maurice View Post
My first rule when servicing these types of amplifier is to change the coupling caps to the output valves. I also replace as a matter of course the grid leak resistors and if they are out of spec the phase splitters anode load resistors. This is non negotiable. SERIOUS DAMAGE CAN OCCUR IF THESE COMPONENTS ARE NOT REPLACED.
confirmed hence why its best not to power these up just yet!

Quote:
In fact I go further with this, I replace all old paper /wax, Hunts mouldseals and anything that looks suspicious.

I use vishay 2W metal resistors rated at 500V and Vishay axial capacitors rated at either 400V or 630V polyester types and Vishay electrolytic capacitors.
I think to be safe all the components should be changed, it would be nice if most of them were still in range. I always wonder if there is a difference in sound with the type of capacitors used i.e PIO, Poly etc

Quote:
They are fairly simple amplifiers that are easily serviced, but do sound good when working.
[B]You are actually close to me, I am based in NW London Hendon so I will keep your details handy!
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Old 3rd Dec 2017, 12:01 am   #6
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Also if the valves I have test to be bad I would like suitable replacements:

I thought about using Harma Valves from Watford Valves:

https://www.watfordvalves.com/products.asp?ID=1&man=6
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Old 3rd Dec 2017, 12:13 am   #7
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

You do jump in the deep end, don't you...

Just work on one amplifier at a time, it's less confusing that way for everyone.
Those three valves with white tops have lost their vacuum and got air inside. the shiny brownish plating inside the tops (and sometimes bottoms) of most valves is a highly reactive metal called the 'Getter' its job is get rid of any residual gas by chemically reacting with it. It's what pumps down the valve to its final vacuum, and it takes care of very slow outgassing or leaks. When the getter is used up, you're left with a deposit of white salts.

It's much more likely that these valves were killed by mechanical damage than by electrical damage, but it's not impossible that a failure in the coupling capacitors (Mentioned by Michael above in appropriately bold text) could have those three overdriven to great currents and temperatures which could crack the glass. I too would worry about the transformers.

The amplifiers look mostly untouched, though a few resistors have been replaced by lower noise metal film types ( the standard of fitting isn't up to Leak's standard)

These are particularly good amplifiers of their era. Now, what makes them so good?

The chassis are just painted metal, nothing special. Any other firm could do them.
The valves were off the peg and fairly cheap in their day
The resistors and capacitors were mundane types found in ordinary consumer electronics.

The secret sauce lies in the circuit design. There isn't anything wild, but Leak pioneered using appreciably more feedback than their competitors. Very artful design of the transformers are the heart of these designs. These parts are what allowed Leak to use more feedback and to still keep the things stable.

The transformers are the key to the whole thing.

And failing coupling capacitors to the power output valves can kill the transformers. Michael's bold typeface is fully justified.

To some people, "refurbish" means to swap every part in the thing.
To some people "Original" means nothing is changed unless NOS parts of original types can be had. Sanity lies somewhere between these extremes.

David
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Old 3rd Dec 2017, 12:25 am   #8
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

I'm a slow typist and started composing my last post after seeing #4.

Some people swear there are enormous differences in the sounds of different types or even makes of capacitors. Others find this hard to believe and can't find those differences with diligent double-blind testing. The differences simply aren't as huge as suggested, and they may be self-delusion. One side of the argument thinks the other side is deluded, while the other side thinks the first side has defective hearing. It all goes downhill from here...

I like good quality, reliable well-made parts. I won't believe in fairy dust without convincing evidence, and this frees up time so I can get on with listening to some music!

Oh, yes, the Leak preamps were all considered not worth bothering with.

What are you going to listen to?

David
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Old 3rd Dec 2017, 11:02 am   #9
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

From the OP's Post #2 it looks like he plans to use this with (relatively) high-output devices and not MM/MC Phono sources. If so, he need only concentrate on Line In/Aux input signal paths in the Pre-Amp at this stage.
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Old 3rd Dec 2017, 12:29 pm   #10
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Quote:
If so, he need only concentrate on Line In/Aux input signal paths in the Pre-Amp at this stage.
Not even that, Edward - if you pull all the valves from the PointOne preamp and feed the outputs from your CD Player/Ipod/whatever into the "Record" outputs from the PointOne preamp, with the octal umbilical connected to the ST20, you can use it in extremis as a passive preamp for the ST20 (well, a passive volume control, actually) while you're sorting out the power amp side of things.

As others have noted, I have to agree that the PointOne preamp, was - even at best - pretty mediocre. Darn fiddly to work on as well.

Cheers,

Frank

Last edited by frankmcvey; 3rd Dec 2017 at 12:43 pm.
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Old 3rd Dec 2017, 2:57 pm   #11
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

When it comes to replacement parts, as a beginner it's more important that they can be trusted so stick with:
2W metal film resistors that are rated for 500V.
Polyester capacitors (MKT) which are typically bright yellow.
Good quality high ripple current electrolytic capacitors (F&F).

The TL12+ look in good condition. The first step is to perform resistance checks on all the transformers using a DMM.
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Old 3rd Dec 2017, 9:59 pm   #12
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Quote:
Originally Posted by Radio Wrangler View Post
You do jump in the deep end, don't you...
iI certainly do David, only way iI get to push myself and learn and iI am determined to do this! Granted it's a big challenge, but for me it will be hugely rewarding.

Quote:
Just work on one amplifier at a time, it's less confusing that way for everyone.
Agreed

Quote:
Those three valves with white tops have lost their vacuum and got air inside. the shiny brownish plating inside the tops (and sometimes bottoms) of most valves is a highly reactive metal called the 'Getter' its job is get rid of any residual gas by chemically reacting with it. It's what pumps down the valve to its final vacuum, and it takes care of very slow outgassing or leaks. When the getter is used up, you're left with a deposit of white salts.
My assumption was mechanical damage or coupling caps from the research iI have been doing, learning as iI go along

Quote:
It's much more likely that these valves were killed by mechanical damage than by electrical damage, but it's not impossible that a failure in the coupling capacitors (Mentioned by Michael above in appropriately bold text) could have those three overdriven to great currents and temperatures which could crack the glass. I too would worry about the transformers.

The amplifiers look mostly untouched, though a few resistors have been replaced by lower noise metal film types ( the standard of fitting isn't up to Leak's standard)

These are particularly good amplifiers of their era. Now, what makes them so good?

The chassis are just painted metal, nothing special. Any other firm could do them.
The valves were off the peg and fairly cheap in their day
The resistors and capacitors were mundane types found in ordinary consumer electronics.

The secret sauce lies in the circuit design. There isn't anything wild, but Leak pioneered using appreciably more feedback than their competitors. Very artful design of the transformers are the heart of these designs. These parts are what allowed Leak to use more feedback and to still keep the things stable.
This is great to hear from you as again iI have been learning all about this

Quote:
The transformers are the key to the whole thing.

And failing coupling capacitors to the power output valves can kill the transformers. Michael's bold typeface is fully justified.
Confirmed these will definitely be changed

Quote:
To some people, "refurbish" means to swap every part in the thing.
To some people "Original" means nothing is changed unless NOS parts of original types can be had. Sanity lies somewhere between these extremes.
David this is my dilemma, clearly both the ST20 and TL12 + need refurnishing, yes iI would like to go original like it left the factory, chosen components are key here iI believe.

I like testing, experimenting and discovering as such, the TL12+ will be my testing grounds. Both TL12+ will have different components and from there iI will test how they perform and sound based on the components they have.

Quote:
Originally Posted by Radio Wrangler View Post
I'm a slow typist and started composing my last post after seeing #4.

Some people swear there are enormous differences in the sounds of different types or even makes of capacitors. Others find this hard to believe and can't find those differences with diligent double-blind testing. The differences simply aren't as huge as suggested, and they may be self-delusion. One side of the argument thinks the other side is deluded, while the other side thinks the first side has defective hearing. It all goes downhill from here...
Well iI know where this is going for me then, iI do agree with you though hence why iI want to try different components in each TL12+

Quote:
I like good quality, reliable well-made parts. I won't believe in fairy dust without convincing evidence, and this frees up time so I can get on with listening to some music!
Any suggestions and tried and tested parts let me know David!

Quote:
Oh, yes, the Leak preamps were all considered not worth bothering with.

What are you going to listen to?
I listen to classical music, jazz, funk, chart/pop music, traditional hindi/bollywood music, it ranges iI do like Bass though sometimes iI will throw on some rock, hip hop etc.
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Old 3rd Dec 2017, 10:16 pm   #13
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Lovely amps the leaks, and the TL12+s look like quite a late production, as the usual McMurdo valve bases have been changed to a different supplier.

1. To ensure the project is worth continuing with, run a continuity test ( with ohm meter ) on all the transformers, as any failure here will be possibly render the amp 'BER' ( rewinds can be done, at a price ! )
2. Replace only the essential parts to begin with - ALL the TCC 'metalpak' and 'metalmite' caps have to go. The main electrolytic can is paint matched to the chassis but if you're lucky and its powered up SLOWLY, it may reform. In the absence of any suitable tester, Hum on the output will give you a clue that is hasn't
3. Get rid of all the old EL84s and buy some decent new ones - old ones are notorious for 'grid current' which can destroy the amp over time. Do not go down the 'NOS Mullard' route as these are likely to be just as bad.
4. Once the amp is running safe and cool, you should be able to measure the various voltages, against the circuit diagrams to determine anything else which may need changing. This is a good exercise for finding your way around the circuit. The measurements will not be exact, but valve circuits are generally very component tolerance immune.A listening test here will show up any noise ( old EF86s are notorious for 'rustling' ) or hum. Resistors in certain positions can cause noise and if the anode loads ( usually 100K & 91 K ) on the ECC81 are a long way out it can cause increased distortion.
4. Ignore all the articles on how to 'tweak' and 'improve' the amplifier, how xyz valves and caps ' improve the soundstage' and firm up the bass' This is 99% fantasy. The only mod. which is probably worth doing is that of gain reduction around the first stage to get rid of some noise, as both the TL12 and the ST20 are over-sensitive for today's sources. A volume control can be interposed to reduce the level into the amp, but, of course the noise remains.

Leak knew what they were doing with these amps and the under chassis wiring is a joy to behold. For not a lot of money they can give many years more service.

A.
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Old 3rd Dec 2017, 11:05 pm   #14
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Quote:
Originally Posted by yestertech View Post
Lovely amps the leaks, and the TL12+s look like quite a late production, as the usual McMurdo valve bases have been changed to a different supplier.

1. To ensure the project is worth continuing with, run a continuity test ( with ohm meter ) on all the transformers, as any failure here will be possibly render the amp 'BER' ( rewinds can be done, at a price ! )
Check, plan to do this, fingers crossed the transformers are fine and in working order

Quote:
2. Replace only the essential parts to begin with - ALL the TCC 'metalpak' and 'metalmite' caps have to go. The main electrolytic can is paint matched to the chassis but if you're lucky and its powered up SLOWLY, it may reform. In the absence of any suitable tester, Hum on the output will give you a clue that is hasn't
When you say power it up slowly do yo mean by using a current limiter i.e a light bulb

Quote:
3. Get rid of all the old EL84s and buy some decent new ones - old ones are notorious for 'grid current' which can destroy the amp over time. Do not go down the 'NOS Mullard' route as these are likely to be just as bad.
Ohhhh I was hoping to keep these, OK my plan was to get then tested on an AVO device and check they are good. But I am happy to purchase new valves. As I mentioned before I was looking at Harma Valves from Watford Valves.

Quote:
4. Once the amp is running safe and cool, you should be able to measure the various voltages, against the circuit diagrams to determine anything else which may need changing. This is a good exercise for finding your way around the circuit. The measurements will not be exact, but valve circuits are generally very component tolerance immune.A listening test here will show up any noise ( old EF86s are notorious for 'rustling' ) or hum. Resistors in certain positions can cause noise and if the anode loads ( usually 100K & 91 K ) on the ECC81 are a long way out it can cause increased distortion.
Excellent to know, writing this on my notes.

Quote:
4. Ignore all the articles on how to 'tweak' and 'improve' the amplifier, how xyz valves and caps ' improve the soundstage' and firm up the bass' This is 99% fantasy. The only mod. which is probably worth doing is that of gain reduction around the first stage to get rid of some noise, as both the TL12 and the ST20 are over-sensitive for today's sources. A volume control can be interposed to reduce the level into the amp, but, of course the noise remains.
I have been reading about gain reduction and would like to know more about this modification, probably a wise thing to do.

Quote:
Leak knew what they were doing with these amps and the under chassis wiring is a joy to behold. For not a lot of money they can give many years more service.
I am looking forward to these amps being finished and to serve me and the family for many years, thanks A.

A.
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Old 4th Dec 2017, 12:29 am   #15
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Some good advice here for you from earlier posts.

I have a fair bit of experience with the leak El84 stuff and totally agree with the advice.

DON'T get conned by the people who will tell you that PIO capacitors and carbon film (crapon?) resistors are essential. I've been there and trust me, any difference ain't worth the effort.
next myth to bust................. These amps are perfectly fine with modern sources. Don't worry about their highish sensitivity it's really not that much of an issue. If you can hear too much hum etc you're too close to the loudspeaker!
The leak preamps are of their time but can be tweaked up fpr modern line sources. Myself i wouldnt nowadays do this as they are fetching stupid prices on the auction sites and i would hang on to it. they have a useful set of attenuating pots on their line inputs so its possible to use a point1 preamp with a CD player without overloading the first stage.
I use a passive job, thats audiospeak for a potentiometer (volume control) in a box and it works just fine and dandy, anything from 100k to 10k will work well with a modern source and don't get side tracked by people trying to confuse you here.
Or use a modern preamplifier. Some have adjustable gain but even one with the usual gain for a less sensitive modern power amp will work ok as a general rule. Again I have done this so I am not hypothesizing. Accept the fact that the volume control will be used at the quiet end of its rotation and its fine.
You've got yourself some lovely amps and I hope you grow to love them as much as i have mine.
for what it's worth, I would get the stereo20 fettled first. Then i would get the TL12's sorted out. Don't worry about cosmetics, get em right first. I reckon you'll like the stereo20 enough to think about moving the TL12's on and you might even make a small profit. thertes not as much difference as certain pundits would have you think.

Andy.
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Old 4th Dec 2017, 12:35 am   #16
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

I don't have the extensive knowledge of previous posters but I have carried out simple repairs on both of these amps. As advised - keep it simple, track down faults, repair them one at a time and listen. They were well designed and that means reliable and long lived. Use a known, trusted source (not the point one pre-amp). That will be separate issue. Very few valve pre-amps from this period survived in good working order - as opposed to most power amps - feels like another thread - someone will now tell me it's already been done!
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Old 4th Dec 2017, 12:48 am   #17
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Since the era of those Leak amplifiers, mankind has learned how to make much better resistors and capacitors.

Much better means better reliability, longer life expectancy, with lower noise and tighter tolerance in the resistors. Lower series resistance, lower inductance and tighter tolerance in electrolytic capacitors.

Would Harold Leak have used these things if they's been available in his era? No-one can know for certainty, but I'd expect so. He used the best he could lay his hands on from the consumer equipment market.

Should you use them? Why not, they're your amps, it's your choice. Grim Joseph did a Leak restoration using only original type components... duds replaced with ones still in spec. It was an object lesson to see what the original untouched design was like.

Me? I'd probably swap the Rs and Cs for something more reliable if for no other reason. Metal film resistors are lower noise than the carbon composition originals. This is measurable, proven and documented. Some people claim carbon sounds better. This isn't measurable but the claims are documented in various high-end magazines. On these amps, you could expect a reduction in noise.

As A. says above, the Leak amps are too high in gain for modern sources. Attenuating signals works, but it has a noise disadvantage. Reducing the gain of any of these amplifiers is non-trivial. It amounts to having to change the feedback stabilisation time-constants and stage gains - a redesign of maybe the most interesting aspect of these amps.

David
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Old 4th Dec 2017, 4:25 pm   #18
vishalk
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning - Help&Guidance Needed.

Quote:
Originally Posted by yestertech View Post
Lovely amps the leaks, and the TL12+s look like quite a late production, as the usual McMurdo valve bases have been changed to a different supplier.

1. To ensure the project is worth continuing with, run a continuity test ( with ohm meter ) on all the transformers, as any failure here will be possibly render the amp 'BER' ( rewinds can be done, at a price ! )
Will do I found this handy piece of information in the LEAK Book

Click image for larger version

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2. Replace only the essential parts to begin with - ALL the TCC 'metalpak' and 'metalmite' caps have to go. The main electrolytic can is paint matched to the chassis but if you're lucky and its powered up SLOWLY, it may reform. In the absence of any suitable tester, Hum on the output will give you a clue that is hasn't
When you say power it up slowly, do you mean by using a current limiter such as a light bulb?

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3. Get rid of all the old EL84s and buy some decent new ones - old ones are notorious for 'grid current' which can destroy the amp over time. Do not go down the 'NOS Mullard' route as these are likely to be just as bad.
I was hoping to get these valves checked by an AVO valve tester, but I was also thinking of buying fresh new valves from Watford Valves, they supply a range called the Harma Retro.

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4. Once the amp is running safe and cool, you should be able to measure the various voltages, against the circuit diagrams to determine anything else which may need changing. This is a good exercise for finding your way around the circuit. The measurements will not be exact, but valve circuits are generally very component tolerance immune.A listening test here will show up any noise ( old EF86s are notorious for 'rustling' ) or hum. Resistors in certain positions can cause noise and if the anode loads ( usually 100K & 91 K ) on the ECC81 are a long way out it can cause increased distortion.

4. Ignore all the articles on how to 'tweak' and 'improve' the amplifier, how xyz valves and caps ' improve the soundstage' and firm up the bass' This is 99% fantasy. The only mod. which is probably worth doing is that of gain reduction around the first stage to get rid of some noise, as both the TL12 and the ST20 are over-sensitive for today's sources. A volume control can be interposed to reduce the level into the amp, but, of course the noise remains.
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Leak knew what they were doing with these amps and the under chassis wiring is a joy to behold. For not a lot of money they can give many years more service.
Looking foward to it A, thanks for the input. I am positive with everyone's help I will choose wisely and myself and the family can enjoy.

Last edited by vishalk; 4th Dec 2017 at 4:27 pm. Reason: added more pics
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Old 4th Dec 2017, 4:37 pm   #19
vishalk
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

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Originally Posted by bikerhifinut View Post
Some good advice here for you from earlier posts.

I have a fair bit of experience with the leak El84 stuff and totally agree with the advice.

DON'T get conned by the people who will tell you that PIO capacitors and carbon film (crapon?) resistors are essential. I've been there and trust me, any difference ain't worth the effort.
Noted thanks for establishing that, guess it's down to personal preference, then again we have come along way in technology and materials with regards to components.

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next myth to bust................. These amps are perfectly fine with modern sources. Don't worry about their highish sensitivity it's really not that much of an issue. If you can hear too much hum etc you're too close to the loudspeaker!
This was worrying me actually, I'll keep it stock and try it on my preamplifiers and see how it performs.

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The leak preamps are of their time but can be tweaked up fpr modern line sources. Myself i wouldnt nowadays do this as they are fetching stupid prices on the auction sites and i would hang on to it. they have a useful set of attenuating pots on their line inputs so its possible to use a point1 preamp with a CD player without overloading the first stage.
I use a passive job, thats audiospeak for a potentiometer (volume control) in a box and it works just fine and dandy, anything from 100k to 10k will work well with a modern source and don't get side tracked by people trying to confuse you here.
I was thinking and researching this, I was going to use something like an ALPS potentiometer.

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Or use a modern preamplifier. Some have adjustable gain but even one with the usual gain for a less sensitive modern power amp will work ok as a general rule. Again I have done this so I am not hypothesizing. Accept the fact that the volume control will be used at the quiet end of its rotation and its fine.
You've got yourself some lovely amps and I hope you grow to love them as much as I have mine.
They don't even work and I am already smitten!

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For what it's worth, I would get the stereo20 fettled first. Then I would get the TL12's sorted out. Don't worry about cosmetics, get em right first. I reckon you'll like the stereo20 enough to think about moving the TL12's on and you might even make a small profit. thertes not as much difference as certain pundits would have you think.
Good Plan Andy I will start on the ST20
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Old 4th Dec 2017, 4:40 pm   #20
greg_simons
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

My own humble contribution would be not to change the polystyrene capacitors around the front end unless they're faulty, Leak chose those types carefully for their low dielectric absorption and stability, substituting different types will badly alter the negative feedback phase response.

Greg.
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