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Leak TL/12 Plus / Point One Plus

Discussion in 'classic' started by Tony L, Dec 15, 2017.

  1. Tony L

    Tony L Administrator


    All done bar the Ukrainian C1 which I think is stuck in customs. It’s an odd one as the listing has now been removed from eBay, but I have Ukrainian tracking that looks legit, so something is coming! It claims to be in UK customs. That done and it is time to check for fire and explosions...


    The F&T smoothing caps are in. I look at this as a temporary solution as it bugs me, if I can find a zero-risk way of evacuating the existing caps and re-stuffing them I’ll do it at some point in the future. At least it is absolutely non-destructive and fully reversible.

    The wires on one amp to the big can cap were very tight so I’ve ended up jumping the ground connection onto and off the old cap ground with a fresh bit of wire so there is some slack and nothing is under tension if the F&T takes a knock. I assume this is ok electrically as it’s just ground? If not please let me know!
    Mike P and John_73 like this.
  2. snowman_al

    snowman_al pfm Member

    That looks okay Tony.
    Just make sure the new smoothing cap cannot swing down and allow the pink wire tag to touch the case of the original smoothing cap or there will be a bang! ...
    If it is C1 (0.001uF) caps you are waiting for, then there is no harm in testing / trying them without. You can add them later.
    Tony L likes this.
  3. Tony L

    Tony L Administrator

    There is a good 3mm or so clearance and they can’t swing down any further in that direction (only back the other way), so unless there is enough voltage to actually spark and jump that sort of gap I assume I’m ok! They are actually very solidly held in place. In hindsight I wish I’d stuck a bit of heat-shrink on for neatness, but I can’t really be bothered undoing it all now!
  4. Tony L

    Tony L Administrator

    Regarding dating Leak finishes etc: I’ve just had a quick look through some old Hi-Fi Yearbooks and the 1960 issue (which one would assume went to press late-59) has the Stereo 20 in bronze with white text. That looks to be the first picture of that amp to appear. Hi-Fi Yearbook were terrible at updating pictures so the same one tended to get reused year on year, so no idea when the dark grey finish came in. They were still running the same old champagne/black picture for the TL12 Plus in ‘67, and they’d have been dark grey and looking towards retirement by then! I think we can pretty safely assume champagne is pre-1960, bronze 60-64/5 or so, and dark grey beyond that.

    Edit: flicking through Pier Pablo Ferrari’s ‘Hi-Fi’s Golden Age’ book I notice a Sept ‘59 Wireless World ad that has a bronze/white finish Stereo 20. That means the champagne S20 was only around a year or so at most, which I guess explains how few one sees, especially given stereo was a new thing then.

    PS I stuck some voltage through the mains transformers earlier as suggested in post #127 and I suspect they are both ok. The GZ34 rectifier seems to come up ok too and both amps seem to be behaving similarly from a PSU perspective. Not tried anything more than that, I’ll wait for the final capacitors to land before going further.
    Last edited: Apr 10, 2021
  5. Darmok

    Darmok "Didactic Prophylaxes"

    A bought pair of champagne coloured Leak TL25+s, that was my first foray in to vintage audio in 1985.

    Bought as disassembled with all the components removed from the tag boards and supplied with a quartet of almost unused clear glass Marconi-Osram KT66s.

    Interesting that the TL25+ can run KT66s as well as proscribed EL34s.

    Once reassembled, they sounded ok but a bit hissy, condition of the pair were fair to good in appearance, I sold them when I eventually found a pair of charcoal finish Leak TL50+s.

    The finish of the champagne TL25+ and my Stereo 20 lacked the sheen of the later bronze and charcoal versions, almost crude by comparison.

    Since then I have owned and heard every Leak vintage valve amp excluding the Leak Stereo 50 and the TL25A.

    I even have a Leak Type 15. :D

    I have read in a few places online that put the Leak TL25+ as the best sounding valve amp against the rest with the TL25A slightly behind.

    Well, I tried to locate a picture of a Type 15 without success but stumbled on this, a cached article called KT66 v EL34 Hi-Fi...


    Grab it before it evaporates into the ether.
    Raoul Duke likes this.
  6. Tony L

    Tony L Administrator

    Yes, I’d agree with that. The TL12 Plus certainly don’t have the beautiful deep gloss shine of my Stereo 20. Still nice looking things though and I am going to give them a wax when I’ve finished the build. As ever Leak were better at painting the chassis than the transformer covers or can cap. That seems a constant across all the amps I own.

    One of the things that attracts me to the TL12 Plus and Stereo 20 (and things like the Leben, WAD etc) is good EL84s can still be had for less than LOLprice. In any sane world I’d have had a pair of Quad IIs pass through, but the price of GEC KT66s is just insane. I know they last ages, but it would still wind me up! I’m lucky in that I just don’t need brute force, my Tannoys a very efficient and the LS3/5As or JR149s so small I’d not want to play them loud regardless of how much power I had available. I’ve built up a pretty decent stash of EL84s, about eight quads in lightly used or NOS condition plus a few odd ones that might extend the lives of some quads (e.g. I’ve got a couple of additional Blackburn Mullards as well as the quad currently in the S20), so hopefully a lifetime’s supply as a secondary system amp. Even so I might land a few more cold-war Russian 6p-14p at some point just to be sure.

    PS Type 15 looks cool (I’ve got Stephen Spicer’s ‘Firsts In High Fidelity’ book, which I think is due for an update/reprint shortly)! I take it you just have one? Good luck finding another! There’s some really cool looking very early stuff Leak built for Partridge before even that.
  7. Darmok

    Darmok "Didactic Prophylaxes"

    Your TL12s do look immaculate, my picture posted above of a pair of point one 12s is not my pair but from a collector in Australia, I will try and locate the pictures taken by a professional photographer who wanted to photoshoot them when I loan the Leaks to him, a very nice pair but not as good as the above pair.

    Mmmm, the world has gone insane since the global broadband roll out and of course e-bay.

    I went to one of the very first audio jumble events in the "Gandhi Hall" in central London organized by John Howes.

    Brand new GEC KT66s boxed, £3 each, I still have the four of them unused.

    Yes, a lonely Type 15 along with a single Audiomaster 11a, been searching for a partner like forever only as a barter deal, I have a spare TL12.1 to trade.

    Ironically the Type 15 was the lowest price I had to pay for out of the rest of them.

    Walking past a charity shop, on the pavement outside I spot an old Garrard pre 301 auto changer like new in its original packaging, price..... 50 pence.


    I swapped the Garrard for the Type 15 amp, the seller wanted the Garrard for what ever reason and didn't know exactly what the huge wooden afrormosia WW2 mobile disco contained apart from a pair of Collaro 78 rpm turntables, the Type 15 was hidden out of sight round the back.

    He told me it was a 60 watt valve amp, I didn't challenge him. ;)

    Made for BBC radio Norfolk by Leak to celebrate the end of the war, apparently "Charlie Chester" used it regularly.


    It is fitted with an extra valve on the chassis, a mercury vapour rectifier used to switch on and off the high voltage to the output valves via a relay circuit, an instant mute switch, a very nice feature for an outdoor mobile disco.
    torstoi and Tony L like this.
  8. Tony L

    Tony L Administrator

    Just noticed this listing on eBay and I’ve gratuitously stolen the image of the schematic as it looks to be a late-period one with the changes:


    The resolution is pretty poor, but it looks to match the reverse-engineered one on VinylEngine and elsewhere:


    As such it hopefully adds to our collective knowledge and I hope the image owner doesn’t mind my lifting it (I’m plugging his listing in return!). It officially documents the change to 470K, and also indicates the TL12 Plus got the 280V mains transformer that found it’s way onto later Stereo 20s. My understanding is these resistor values were retrofitted to any amp returned to Leak regardless of the transformers fitted as a safety/longevity fix, though finding formal documentation of that is hard to find. I get the impression later documentation is hard to find, certainly my bronze Stereo 20 has the earlier schematic despite shipping with later resistor values (it has the later output transformers, so they clearly arrived before 1961).
  9. Darmok

    Darmok "Didactic Prophylaxes"

    The A4 envelope of circuit diagrams sent to me from Leak contained several what appeared to be the same circuits but with hand written amendments.

    It did enable me to re-assemble my first pair of TL25+s and repair the TL50s I bought a little later.

    Nothing to add here at this time as the diagrams are not at hand to post here or peruse.
  10. Mike P

    Mike P pfm Member

    Lovely job Tony.

    I've got another ST20 in the back of a cupboard here waiting to be done.
    Tony L likes this.
  11. John_73

    John_73 pfm Member

    Both amps are looking great Tony - truly fantastic work there! I just haven’t had the energy to do anything further to my Stereo 20 recently (truly, M.E. is a frustrating sod of an illness, really curtails doing projects like this) and it’s been two years since I started it now. Prepping and painting the transformer shrouds is still holding me back. So I get a lot of joy instead out of seeing others restore their amps. Pity that one cap is holding things back a tad, but touch wood it arrives this week. If not I think I may have a couple spare K40Y-9s from my Stereo 20 project.
    Darmok and Tony L like this.
  12. Tony L

    Tony L Administrator

    Sorry to hear that. I’d just chip away at it slowly if you can. Your quality of work is superb. I guess the problem is finding the physical space to leave a project in progress fairly long-term. I just don’t have anywhere so do tend to plow on through until I run out of components. Even so I’m surprised how many hours it actually took. I didn’t keep track, but it must be a couple of full 8 hour days once making the leads and dim-bulb tester is factored in. Whilst I grasp pros will be way faster than me due to experience and have economies of scale on purchasing etc I can’t understand how the likes of Classique Sounds turn a profit doing this. My basic component cost was >£150 (ok, I bought nice stuff!), and then hours and hours of labour. I love doing it as a hobby and would certainly encourage others to do the same (assuming they understand the concept of high voltage!), but I’d not want to do it as a job.

    PS For anyone keeping count even with a really cheap first amp (say £50 after I’d sold the preamp) I’m in at about £950 here including components, leads etc, but not including any valves (which thankfully I have), plus obviously a lot of hours. I can get that figure down a bit if I can sell the boxed mono Varislope and the mono Point One preamps. I’ll bung them in the classifieds at some point...
    John_73 and Darmok like this.
  13. Tony L

    Tony L Administrator

    Ukrainian caps turned up, so they are fitted. I also stuck some heatshrink on the can cap terminals. All dim-bulb then proper smoke-testing complete and amp #2 is working fine and sounding I assume exactly how it should. Sounds fine.

    There is however an issue with amp #1. It has virtually no output. Very, very quiet, though still clean and undistorted. Exactly the same valve set used, and I’ve tried both the 8 and 16 Ohm transformer taps. I’ve also used the same interconnect. All valves look to be functional, i.e. are glowing/generating heat exactly as expected. There is just maybe a fifteenth the output of the other one at the speaker terminals. The characteristic Leak hum on power-on which subsides after a short while is present at the normal level though (it subsides as usual).

    What is my next step? The amps are to my eyes absolutely identical, so my fear is either the output transformer is toast, or there is something wrong on the hidden side of the board. I was very careful and double-checked I hadn’t bridged anything on the valve sockets I soldered etc.

    Here is a decent picture of #1 as it stands right now:


    Better resolution here.
    torstoi and John_73 like this.
  14. John_73

    John_73 pfm Member

    Well done on the amps, though sorry one is not working as it should. Isn’t something simple like the plug in ohm selectors on the output transformers needing a clean is it? Dirty valve pins? I’d look to simple reasons first, or any obvious dry joints etc.
  15. Yank

    Yank Bulbous Also Tapered

    Have you done voltage charts for both amps?
  16. Tony L

    Tony L Administrator

    It’s all spotless, I really thoroughly cleaned everything with Deoxit etc, and the impedance selection plugs are far nicer quality than on the Stereo 20 and have great continuity (I really polished them up). I cleaned thoroughly the valve bases too, but I’ll check the bases with a loupe later to see if anything is amiss visually.

    Prodding around the unpowered amps gives the impression the output transformer may be ok, at least it measures the same as the other working one with regards to impedance as far as I can get to it (annoyingly I bolted, soldered and heat-shrunk a bloody big cap exactly in the way).

    FWIW to my limited understanding if the output transformer was broken I’d get no output at all? As it is I get the initial characteristic Leak switch-on hum at the normal level, which then subsides as normal, and then clean clear music at a very, very low level. Does this possibly imply the issue may be somewhere upstream, i.e. I’m not getting input gain for some reason? I’d have thought the normal ‘Leak level’ start-up hum implied the output stage was functioning? The lack of level is almost like having an amp on the wrong input and hearing crosstalk.

    I don’t even know what one is! I’m absolutely not an electronics engineer, I’m just someone who can solder very neatly and follow instructions. If someone tells me where to stick the probes I’ll happily post values. I’ve even got an oscilloscope available, but again I’ll need instructions as I am only a beginner.
  17. Yank

    Yank Bulbous Also Tapered

    Just a chart of the measured DC voltages at every pin of every tube would be a good start.

    In addition to checking the jumpers on the backside of the board, I'd also check for any "off by one" errors (something connected to the wrong tube pin) and "off by ten/hundred/thousand" errors (wrong resistor value).
  18. Tony L

    Tony L Administrator

    I’ll do that over the next couple of days. I’ve already done the valve pin thing - I went through and double checked everything, checked for any bridges or dropped solder blobs etc before even doing the dim-bulb test. I’ve only checked my work though, not what was in the amp initially.

    I’m hoping folk here with better colour sense than me can maybe double check the resistors values from the images, but I can’t see how they can be wrong as I labelled the bags with the Leak resistor numbers (R1, R2 etc) and installed them in sequence. Prior to that I actually tested what was in each bag corresponded to what was written on the bag. At no time at any stage was more than one bag of resistors open. I worked on the assumption I am 100% colour blind (which I’m not by any stretch, I’m just not that great on the red spectrum). I really tried for an idiot-proof process here.

    Jumpers the back of the board loom will be the last resort as it involves a lot of faff to get to.

    PS I’m obviously curious as to suggestions as to what fault conditions could produce the specific symptoms I describe? Knowing what is most likely/what to check first would obviously be a big plus.
  19. John_73

    John_73 pfm Member

    From what you’ve said, all the heaters seem to be working fine, so next check the following if you're confident taking readings from a live amp - Never touch the amplifier chassis with one hand while probing with the other hand. Not a bad idea to keep one hand in your pocket unless more experienced.

    Connect the DC negative probe securely to an earthing point on the chassis, then take some DC readings at the following locations:

    DC voltages ‘after’ R22 (315V), R15 (280V), and R7 (200V) (top ‘line’ on the circuit diagram you posted a few posts above). That’ll show if the anodes are getting their juice or not. Double-check the resistor values for R5 and R23 too for starters.
  20. snowman_al

    snowman_al pfm Member

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