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Old 4th Dec 2017, 5:26 pm   #21
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 Radio Wrangler View Post
Since the era of those Leak amplifiers, mankind has learned how to make much better resistors and capacitors.
Agreed David

Quote:
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.
Again agreed, just getting caught up I guess in all the hype and marketing

Quote:
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.
What were the results? I'll do a search for that.

Quote:
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.
Again need to research these articles, be a good read for me

Quote:
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.
Will see how it goes David, but I would like to try the gain reduction at some point. Going to rebuild the ST20 first!
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Old 4th Dec 2017, 6:10 pm   #22
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

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Old 4th Dec 2017, 6:10 pm   #23
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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 greg_simons View Post
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.
Thanks Greg anything which is original and still working and within tolerance will be kept.
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Old 4th Dec 2017, 6:23 pm   #24
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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 greg_simons View Post
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.
That's sensible advice in any case.
For the record Greg, my 1962 vintage stereo20 used Silver mica caps in the feedback network and there they still sit to this day. It's just the original Paper in oil TCC or similar coupling caps that are "replace on sight" jobs. One thing is for sure, these amps are a pleasure to work on because of the neat component layout on the tag board and taking one's time to replace resistors and capacitors one at a time is a fairly simple task. I'd also replace the electrolytic cathode bypass caps if original as they are cheap as chips (don't go mad on special grade caps, any good workmanlike electrolytic with a sufficient (25V or over) working voltage will work admirably. I chose higher working voltage ones simply to keep the sizes looking similar to originals. I think it's been mentioned previously, using 2W metal film resistors keeps the look underneath more proportionate if that sort of thing is important to you.
Good luck and I hope the amps give you the listening pleasure that mine have over the years. With good modern parts mine has stayed reliable for the last 15 years.
Lastly, and I think most here would agree, don't get hung up on expensive replacement valves. If the EF86 (TL12+) and ECC83/81(TL12+) valves are still ok and a listen and check of the voltages will give you a good idea, then leave them in as they last very well. I'd think about replacing the EL84 output valves again I'd check the cathode voltages and if inside the design voltages they should be ok, but stick to the reasonable cost end of the market, you don't really need matched pairs as the cathode bias design pretty much compensates for differences in the valves. Again this is from my own personal experience as much as anything else.
That Book of Steven Spicers is an excellent reference tome and full of good info, including the differences between the output transformers.
A.

Last edited by bikerhifinut; 4th Dec 2017 at 6:28 pm. Reason: Unnecessary info.
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Old 4th Dec 2017, 6:37 pm   #25
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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.
Good to know I think I'm just getting caught up in the hype and marketing, down to personal preference. I do like the idea of a good old PIO capacitor though. Like David said technology and components have come along way since the leak days

Quote:
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!
Now that is interesting to hear! I have different preamplifiers so I will try them out to see what suits and sounds better

Quote:
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. theres not as much difference as certain pundits would have you think.
Thanks Andy, going to sort the ST20 first, I am already smitten by these amps and they don't even work yet! The TL12's will be my testing amps, by means of trying different components and mods! But I think you maybe right, the ST20 is a keeper and I may move the TL12 on
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Old 4th Dec 2017, 8:04 pm   #26
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

One other very important point, never under any circumstances disable or increase the wattage of the ht line fuse resistor, it's meant to overheat and drop off the tag strip thereby protecting the priceless output transformers should a fault develop in the output stages, many a good twenty has been reduced to scrap by such action.
greg.
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Old 4th Dec 2017, 9:23 pm   #27
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Modern components have had to get better. The trend to more complex equipment having many more parts would have brought about very short mean times between failures if things had stayed as they were. Additionally, expectations have risen so the reliability of the overall equipment had to do better than stay the same.

Reducing the sensitivity of these amplifiers amounts to either re-doing one of the major pieces of work in their design (and then questioning just what the amplifier is afterwards). These amplifiers were designed pretty much at the state of the art in terms of how much negative feedback could be employed in a transformer-output amplifier without stability issues. If the closed-loop gain is to be reduced, then the open loop gain needs a matching reduction in order to preserve the stability margins

Not changing it means taking a large signal from a CD player for example, attenuating it down to a hundred millivolts or so, and then the Leak amplifying it up to loudspeaker drive levels. This conveys an inevitable disadvantage in noise performance. It's not bad, but it's inelegant.

The hype and marketing does tend to suck you in. That's what it's supposed to do. the marketing people see it as a route to either increase profits by greater turnover, or as a way to increase profits by making greater prices seem acceptable. You have to develop a thick skin to all the claims and strip them down to the reality (marketing people really don't like this)

Also there are people using it to stroke their egos.... "I'm a mage of the seventh level and my highly trained ears can hear things yours cannot. Trust me, there is a difference and it's a Huge one!" Their logic misses out on the thought that even if there is a difference, if you cannot hear it, then it doesn't matter at all to you. They wish the gratification of you following their lead and buying whatever they've just blown the family heritage on. Imitation is the sincerest form of flattery.

There are people who just got sucked in by all the fancy wordery. They're inocents, really.

There are differences which really can be heard, maybe not as much as the aficionados claim, but differences none the less. I find it interesting that the aficionados always hear differences in anything, and always know which is better. Me, I can hear differences in some things, none in others, and often I can't make my mind up which is better. I don't trust my senses 100%, I know my hearing and sight can be tricked by acoustic and visual illusions and I know that I sometimes do the tricking. It's good to have reality checks to keep myself honest.

Those Leaks are gorgeous pieces of kit, they were well designed by honest engineering people long before sonic fairy dust was invented. They are nice to look at, nice to contemplate and good to listen to music with.

David
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Old 4th Dec 2017, 11:51 pm   #28
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by greg_simons View Post
One other very important point, never under any circumstances disable or increase the wattage of the ht line fuse resistor, it's meant to overheat and drop off the tag strip thereby protecting the priceless output transformers should a fault develop in the output stages, many a good twenty has been reduced to scrap by such action.
greg.
Greg I was thinking of replacing the HT line fuse with a 20mm 350mA Fuse and Holder. I was also thinking of changing the Bulgin power socket to a IEC one with a switch and fuse.

http://www.amplabs.co.uk/Leak%20stereo%2020.htm

I like what amplabs do with the ST20
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Old 5th Dec 2017, 12:18 am   #29
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Hi, again,
excellent idea replacing the fuse resistor with a real glass fuse, I have no idea why they never fitted one in the first place although the cost of a bulgin fuse holder and glass fuse was way more expensive than a simple resistor, on the subject of mains sockets if they are broken or missing plugs,,common, probably best replace with modern stuff, genuine plugs and sockets are very expensive as sellers know what their end use will be.
as many other comments here say they are beautifully made and certainly inspired me as a young tech to do very neat work to a high standard.
greg.
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Old 5th Dec 2017, 12:25 am   #30
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

The amplabs stereo 20 webpage seems quite sensible, but with one exception. 1N4007 are very slow diodes because of how their high voltage rating is achieved. They turn off late and with a snap which creates strong RF interference. It is most counter-intuitive, but higher speed rectifiers create lass noise. I'd go for a better diode in any HT power supply. in this case, the GZ34 may be doing all the work and cutting off before 1N4007, but that type is best avoided.

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Old 5th Dec 2017, 12:31 am   #31
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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 Radio Wrangler View Post
Modern components have had to get better. The trend to more complex equipment having many more parts would have brought about very short mean times between failures if things had stayed as they were. Additionally, expectations have risen so the reliability of the overall equipment had to do better than stay the same.
I had some vintage Japanese amplifiers and preamplifers 70's, 80's and 90's. the amount of components used was a joke. When I used to service my equipment, or had to change components I just thought to myself "This sh@t is not worth keeping, it won't last 20-30 years and I'll be damned if I'm changing a hundred plus or so components. I mean look how many components and parts make up a valve amp, then compare that to today's technology. I'm drawn to valve amplifiers and preamplifiers because they will last a lifetime and you can fix them if you're competent. Oh and of course because they sound wonderful as well.

Quote:
Reducing the sensitivity of these amplifiers amounts to either re-doing one of the major pieces of work in their design (and then questioning just what the amplifier is afterwards). These amplifiers were designed pretty much at the state of the art in terms of how much negative feedback could be employed in a transformer-output amplifier without stability issues. If the closed-loop gain is to be reduced, then the open loop gain needs a matching reduction in order to preserve the stability margins
Sounds like a great deal of trouble to me, if thats how HJ Leak designed it, that's how I will keep it. Plus you lost me at "open loop" but I kinda get what you are saying.

Quote:
Not changing it means taking a large signal from a CD player for example, attenuating it down to a hundred millivolts or so, and then the Leak amplifying it up to loudspeaker drive levels. This conveys an inevitable disadvantage in noise performance. It's not bad, but it's inelegant.
I have three pre amplifiers here all with different gain outputs so one of them should suffice, I also have a ALPS 10k potentiometer

Quote:
The hype and marketing does tend to suck you in. That's what it's supposed to do. the marketing people see it as a route to either increase profits by greater turnover, or as a way to increase profits by making greater prices seem acceptable. You have to develop a thick skin to all the claims and strip them down to the reality (marketing people really don't like this)
Thick skin in being built as we speak!

Quote:
Also there are people using it to stroke their egos.... "I'm a mage of the seventh level and my highly trained ears can hear things yours cannot. Trust me, there is a difference and it's a Huge one!"
hahaha I'm pi$$ing myself with laughter because I like to stroke my own ego just like that!

Quote:
Their logic misses out on the thought that even if there is a difference, if you cannot hear it, then it doesn't matter at all to you. They wish the gratification of you following their lead and buying whatever they've just blown the family heritage on. Imitation is the sincerest form of flattery.

There are people who just got sucked in by all the fancy wordery. They're innocents, really.

There are differences which really can be heard, maybe not as much as the aficionados claim, but differences none the less. I find it interesting that the aficionados always hear differences in anything, and always know which is better. Me, I can hear differences in some things, none in others, and often I can't make my mind up which is better. I don't trust my senses 100%, I know my hearing and sight can be tricked by acoustic and visual illusions and I know that I sometimes do the tricking. It's good to have reality checks to keep myself honest.
I tell you what David I am similar to you, this is one of the many reasons I am doing this project and many more for the future. I like to think I have a keen ear and a good sense of what feels and sounds good.

I mean I take it as far as have four sets of different speakers, from ones I have built myself to commercial made such as Kef, Tannoy etc. I like to try these speakers on different amplifiers, different sources, preamplifiers just to see if I notice a difference and choose a system that best suits my listening pleasures.

Quote:
Those Leaks are gorgeous pieces of kit, they were well designed by honest engineering people long before sonic fairy dust was invented. They are nice to look at, nice to contemplate and good to listen to music with.
I like the fact that I can buy a piece of British audio history, learn about it, share my enthusiasm with the members on here and have the reward of repairing them to former glory.

Vishal
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Old 5th Dec 2017, 12:36 am   #32
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by greg_simons View Post
excellent idea replacing the fuse resistor with a real glass fuse, I have no idea why they never fitted one in the first place although the cost of a bulgin fuse holder and glass fuse was way more expensive than a simple resistor, on the subject of mains sockets if they are broken or missing plugs,,common, probably best replace with modern stuff, genuine plugs and sockets are very expensive as sellers know what their end use will be.
as many other comments here say they are beautifully made and certainly inspired me as a young tech to do very neat work to a high standard.
You're right Greg, I just checked the Bulgin socket and it's in good condition, why change it eh? Yes the neatness and standard of work on these amplifiers is beautiful actually. I'll endeavour to do the same and keep to that standard.
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Old 5th Dec 2017, 10:27 am   #33
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by vishalk View Post

Quote:
Originally Posted by Radio Wrangler View Post
... 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 ...
What were the results? I'll do a search for that.
My restoration was of a pair of Leak TL/12 Point One mono amps. I kept all of the original transformers of course.

The capacitors were a real problem. Every single one of the paper-in-oils had gone leaky and were threatening to destroy the valves and/or transformers. I contemplated emptying the cans of their old contents and hiding small modern plastic capacitors inside them. But in the end I bought some modern paper-in-oils (there are a few specialist manufacturers left, but their products aren't cheap), removed their markings, printed out more authentic looking markings on water-slide film, stuck these on the new capacitors and covered the whole lot with transparent heatshrink tubing. The result would not have fooled any of the specialists here but, as my father-in-law used to say, "a man on a galloping horse might not have noticed". The HT smoothing capacitor in one of the amps had failed. This was originally a 3-section paper-in-oil unit made specially for these amplifiers. Since it really affects the appearance of the amplifier I did, in this case, cut open the bottom of the can, remove the contents (the 'oil' is more like a Vaseline grease), fit modern polypropylene films and resolder the base back in place. With a dab of black paint this really is a convincing repair.

I found in-spec carbon resistors. This was not so easy as the carbon composition ones all tend to drift high in value with age, whether they've been used or not. I had to sort through quite a lot to get enough good ones. The carbon films (which used to be called 'high stability, cracked carbon') tend to be completely stable and just as good now as when they were manufactured. This really matters for the phase-splitter anode loads which need to be the right value to preserve drive balance to the output stage. When I'd replaced all the resistors one amp was meeting its spec and the other wasn't. The bad one had about twice as much harmonic distortion as it should have. It took me a while to find the fault. It turned out that one of my replacement carbon comp resistors (the one that takes the feedback signal from the output back to the input stage) measured OK with a DMM but was actually nonlinear. So its resistance changed with voltage. When it was exposed to the full output voltage (12 watts into 8 ohms is 9.8V RMS = 13.9V peak) its resistance changed and this distorted the waveform. I replaced it and all was then well .

One other thing I would say - does commercial value matter to you ? If it does then you should be aware that tearing out all of the original components and sticking new ones in will devalue the amplifier. Most of the people who buy these want something old, not something that's been 'got at' as one potential buyer once said of an amp I'd restored. If you do take components out I'd recommend at the very least that you never cut the wires. Instead take time and with care you will get them out undamaged. Then put them in a safe place. When you come to sell the amp you can tell the buyer that you have all of the original parts and if they want to put any (or all !) of them back then they can. As far as I know they never do. But the thought that they could if they wanted to seems to cheer them up a lot.

Cheers,

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Old 5th Dec 2017, 7:42 pm   #34
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

When did resistors and general components become so ****** expensive?

https://www.hificollective.co.uk/com...resistors.html

Been doing some reading:

https://www.eetimes.com/document.asp?doc_id=1278251

I found this handy list which was a great help in identifying the components.

So i can make all the 1/2w resistors 2W as suggested and choose a low tolerance and low noise type. What is the deal with tolerances?

Click image for larger version

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Would you agree with this comparison of resistor types?

Some examples of other peoples work.

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LEAK STEREO20 PARTS LIST
Resistors
Qty Designator Original Value Replaced with
2 R1 1M, 1/2W 1M, 1/2W
2 R2 22K,1/2W 22K,1/2W
2 R3 2K2, 1/2W 2K2, 1/2W
2 R4 100R, 1/2W 100R, 1/2W
2 R5 100K, 1/2W 100K, 1/2W
2 R6 3M3, 1/2W 3M3, 1/2W
2 R7 91K, 1/2W 91K, 1/2W
2 R8 1K, 1/2W 1K, 1/2W
2 R9 22K, 1W 22K, 1/2W
2 R10 100K, 1W 100K, 1/2W
2 R11 3M3, 1/2W 3M3, 1/2W
2 R12 1M ,1/2W 1M ,1/2W
2 R13 1M ,1/2W 1M ,1/2W
2 R14 270R, 1W 270R, 2W
2 R15 270R, 1W 270R, 2W
2 R16 10K, 1/2W 10K, 1/2W
2 R17 10K, 1/2W 10K, 1/2W
2 R18 12K, 1/2W 12K, 1/2W
1 R19 47K, 1/2W 47K, 1/2W
1 R20 4K7, 1/2W 4K7, 1/2W
1 R21 100R, 3W 100R, 3W wirewound

Capacitors
Qty Designator Original Value Replaced with
2 C1 1nF, 400V 2x470pF in parallel
2 C2 50uF electrolytic,12v 47uF, 25V
2 C3 0.1uF, 350V electrolytic not replaced
2 C4 0.25uF, 350V electrolytic 220nF, 450V
2 C5 0.02uF, 350V electrolytic 22nF,450V
2 C6 0.25uF, 350V electrolytic 220nF, 450V
2 C7 50uF electrolytic,25v 68uF, 50V
2 C8 50uF electrolytic,25v 68uF, 50V
2 C9 200pF not replaced
1 C10 32uF, 400V CAN1 47uF, 450V
1 C11 32uF, 400V CAN1 47uF, 450V
1 C12 32uF, 400V CAN2 47uF, 450V
1 C13 32uF, 400V CAN2 47uF, 450V
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Old 5th Dec 2017, 7:52 pm   #35
vishalk
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by GrimJosef View Post
My restoration was of a pair of Leak TL/12 Point One mono amps. I kept all of the original transformers of course.
Hey i visited your website before i decided to take the challenge of doing the restoration myself. Do you scans or copies of the articles in Hi-Fi world?

Quote:
The capacitors were a real problem. Every single one of the paper-in-oils had gone leaky and were threatening to destroy the valves and/or transformers. I contemplated emptying the cans of their old contents and hiding small modern plastic capacitors inside them. But in the end I bought some modern paper-in-oils (there are a few specialist manufacturers left, but their products aren't cheap)
Please send me there links, i would like to use British made components

Quote:
removed their markings, printed out more authentic looking markings on water-slide film, stuck these on the new capacitors and covered the whole lot with transparent heatshrink tubing. The result would not have fooled any of the specialists here but, as my father-in-law used to say, "a man on a galloping horse might not have noticed".
Thats very clever and i like the special touches you added.

Quote:
The HT smoothing capacitor in one of the amps had failed. This was originally a 3-section paper-in-oil unit made specially for these amplifiers. Since it really affects the appearance of the amplifier I did, in this case, cut open the bottom of the can, remove the contents (the 'oil' is more like a Vaseline grease), fit modern polypropylene films and resolder the base back in place. With a dab of black paint this really is a convincing repair.
I've read this is a messy Job!

Quote:
I found in-spec carbon resistors. This was not so easy as the carbon composition ones all tend to drift high in value with age, whether they've been used or not. I had to sort through quite a lot to get enough good ones. The carbon films (which used to be called 'high stability, cracked carbon') tend to be completely stable and just as good now as when they were manufactured. This really matters for the phase-splitter anode loads which need to be the right value to preserve drive balance to the output stage. When I'd replaced all the resistors one amp was meeting its spec and the other wasn't. The bad one had about twice as much harmonic distortion as it should have. It took me a while to find the fault. It turned out that one of my replacement carbon comp resistors (the one that takes the feedback signal from the output back to the input stage) measured OK with a DMM but was actually nonlinear. So its resistance changed with voltage. When it was exposed to the full output voltage (12 watts into 8 ohms is 9.8V RMS = 13.9V peak) its resistance changed and this distorted the waveform. I replaced it and all was then well.

One other thing I would say - does commercial value matter to you ?
If it does then you should be aware that tearing out all of the original components and sticking new ones in will devalue the amplifier.
I plan to take out all the original components carefully and keep them!

Quote:
Most of the people who buy these want something old, not something that's been 'got at' as one potential buyer once said of an amp I'd restored. If you do take components out I'd recommend at the very least that you never cut the wires. Instead take time and with care you will get them out undamaged. Then put them in a safe place. When you come to sell the amp you can tell the buyer that you have all of the original parts and if they want to put any (or all !) of them back then they can. As far as I know they never do. But the thought that they could if they wanted to seems to cheer them up a lot.
It will be a very long time before i sell these amps, i may never sell them!
Thanks for the input GJ
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Old 5th Dec 2017, 11:42 pm   #36
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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 vishalk View Post
When did resistors and general components become so ****** expensive?
I think you might be in danger of "over analysing" things, if I may be so bold.

HiFi collective are useful for some parts but for things like resistors and most of the capacitors I'd go somewhere else, heck even Maplins do some decent 2W metal film 1% resistors and they are more than good enough for the task. Beware of "boutique" components, just use reputably sourced appropriately specified parts.
I use RS online for much of my parts and although its a bit clanky working one's way through their website I usually find what I need at a reasonable price.
I use 1% tolerance resistors because for the most part they don't cost any more than 5% jobs and I like to know I have got everything bang on the design button. But it's only in areas like the anode loads on the Long tail pair phase splitter (91k and 100k) that getting resistor values bang on might matter. These older valve designs are remarkably tolerant of slight variations from design values.
Like wise capacitors, I use the Vishay polyester 630V DC capacitors as sold in the BVWS shop (other sources are available) and I am more than happy with the results achieved. Electrolytics are any reputably sourced jobs that are suited to the application. Use the nearest preferred values to the originals.

That capacitor C1 1nF was a ceramic type on my stereo20 and again it stayed put. I wouldn't faff around paralleling capacitors here as 1nF (1000pF) is a commonly available value, and its not value critical in that position.

Andy
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Old 6th Dec 2017, 1:31 am   #37
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Back in the day of the Leak amps, basic quality resistors were +/-20% tolerance.
10% tolerance parts got a silver band. 5% parts "High stab" got a gold band and that was about it. You didn't dare to ask what their drift over time was like. These percentages were simply how accurate they were at time of manufacture. 2% was for very special parts in measuring instruments.

Modern materials and manufacturing methods have made 1% parts routine and affordable. What's more they have the stability over time and temperature to make that tolerance meaningful.

The two sites you linked to are hilarious. What makes the prices so high is exclusivity or have I got it the wrong way round? the high prices exclude most people from having them.

They seem to make a big thing about noise performance. I've been involved a bit with noise from resistors. In the RF world, the noisiness of components is of great interest and gets expressed in several ways. "Noise Figure" compares the noise created in some device, system or component to the noise power density created in a perfect resistor at a temperature of 290 Kelvins (about room temp, and an arbitrarily picked convenient number) and expresses the difference in deciBels. Another way is to state the temperature an ideal resistor would have to be at to create the same noise power density. This is easier to visualise. Resistors get noisier the hotter they happen to be. An ideal resistor has a characteristic which is linear, and if you project the line downwards, passes through no noise at all at absolute zero. Bad resistors suffer from excess noise and produce more than ths line at real-world temperatures. Good quality metal film resistors are very very close to the ideal line. They aren't expensive and they aren't made out of unicorn hide and unobtainium. Seeing fancy resistors made out of exotic materials just for fashion and marketing reasons is very funny. Looking at the prices, I suppose they couldn't get real unobrainium and so they faked it with unaffordium.

Straight forward metal film resistors without pretensions will do fine. There are many firms who make dependably reliable ones for pennies. Vishay make lots. Holsworthy are a specialist manufacturer of very close tolerance parts to custom designs when you need them. They appear on the hifi collective webpage as 'Holco' though the prices seem to have inflated in the retailing. About 50p for a 0.1% part if you need them, if you get them from industrial rather than boutique sources.

The industry standard equipment for measuring this is the Agilent N8973A family (up to N8975A) of Noise Figure Analysers, along with the N4000A series of 'smart' noise sources. This equipment can measure the noise created in a near ideal resistor down to about 10 degrees above absolute zero. I originated it, led the hardware development team and handled the metrology aspects and liaised with the National Physical Laboratory over transfer standards for calibration. It was a lot of work, but I think it earned me the right to have a laugh at some of the claims attached to fancy resistors. Pick the right types and you are so close to the state of the art for pennies.

By the way, treating noise as power density gets rid of having to state bandwidth or even resistance value in the formulae. Noise power density from an ideal resistor is kT Watts per Hertz. T is the temperature in Kelvins, k is the Maxwell-Boltzmann constant.

David
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Old 6th Dec 2017, 10:00 am   #38
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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 Radio Wrangler View Post
Back in the day of the Leak amps, basic quality resistors were +/-20% tolerance.
10% tolerance parts got a silver band. 5% parts "High stab" got a gold band and that was about it. You didn't dare to ask what their drift over time was like. These percentages were simply how accurate they were at time of manufacture. 2% was for very special parts in measuring instruments ...
The whole of the above post is a very good one. Just one minor clarification - as I understand it the gold band was only for 5% tolerance. 'High stab' meant that the resistance value was stable over time. This commonly involved a different form of construction (e.g. carbon film versus carbon composition) and was indicated by an additional salmon pink band. When I come to restore a vintage piece of kit one of the more worrying signs is the sight of a lot of 5% resistors, so the manufacturer knew that they needed to be within a tight spec, but the absence of any salmon pink, so I now know that they no longer will be .

Cheers,

GJ
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Old 6th Dec 2017, 2:58 pm   #39
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

After all the theory, which of your amplifiers are you thinking of making a start on first?
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Old 6th Dec 2017, 5:37 pm   #40
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Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Considering they are one of the same i will be starting with the ST20, good place to start

The TL12+ will take longer as i plan to do a complete refurbish including paint work.
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