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Old 5th Dec 2017, 7:52 pm   #35
vishalk
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Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

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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?

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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

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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.

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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!

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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!

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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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