Leak TL/12 Plus / Point One Plus

[Yank]

https://www.ebay.com/itm/Tube-Socke...d=link&campid=5338728743&toolid=20001&mkevt=1

 

[Tony L]

Many thanks, they are close, but not exact (different mount, missing metal centre, so would be visibly different from above) but certainly look to have the right forks. I’m going to wait until the ones I’ve ordered land so I can better understand exactly how these things disassemble (e.g. does the plastic centre easily remove from the mounting plate), what parts are in common between variants etc, but that done I do plan to stockpile a fair few so there is no way I’ll get stuck in the future. I have to admit I’ve no intention of blanket replacing all the sockets, it is just way, way too much work!

To my mind the most logical approach is just to replace any broken or sad looking individual forks and to hold a substantial stockpile of spares. That way the amps (I’m including the S20 in this) are all as original as possible, but future-proofed too. It would be nice if I ever sell-up (which I inevitably will in old-age/retirement) to include a couple of NOS sockets with each amp so any future owner can keep them running for another 60 years!

 

[Tony L]

I’ve done the fork replacement, I did the two connected 6.3V AC pins. An absolute PITA, I really can’t over-stress that. Getting the old forks out was a nightmare as you can’t reach them properly with either a solder sucker or side-cutters, I have a feeling I’ve trashed my lovely Japanese Engineer brand side-cutters. Anyway it is done.

Both amps seem to be working fine and seem to be behaving as a pair, e.g. image is centred. No audible hiss, hum or buzz, through this is an exceptionally simple system with inefficient speakers (LS3/5As). I’ve only had them on for 15 minutes or so and will likely finish up soon and have a better listen tonight in a much darker room as I want to be able to see any red-plating or anything well in advance.

I’m running a pair of ‘50s EF86 I liberated from one of the preamps, 80s military Mullard CV4024 (I’ve got loads of them and they are very good), gold-pin 6P14P-EV output valves as they are apparently fine up to 400V and these things run the valves hard, and Blackburn Mullard GZ34s (later types with seven notches in the plates, one being the Tungsram badged one that came with Amp #2). The angle of the amps in the pic is purely practical to get leads to reach without too much stress on pretty flimsy speaker connectors.

PS One thing I’ve learned from frantically googling around is if you change the 1M grid resistors to 470K you have to change the 0.02uF cap to 0.1uF. Do one and not the other and you can end up with an unstable amp. There is a relevant Stereo 20 thread on the WAD forum here. The advice there looking to do exactly what I have done to these amps if you have the early transformer specs.

 

[John_73]

Great stuff! You must feel a real sense of accomplishment now having waited so long to get a second matching amp, and all the work put into servicing them. Great work on those pins too. How are they sounding? Will be very interesting to hear your thoughts on these vs your Stereo 20 in due course.

 

[Yank]

Are you going to try them with the Tannoys?

 

[Tony L]

How are they sounding? Will be very interesting to hear your thoughts on these vs your Stereo 20 in due course.

They sound very decent. I wasn’t thinking “these are incredible” or “ugh, these are just terrible”, so I suspect they are pretty much on the level of the Stereo 20. Basically they sound really good. I’ll run them off and on for a week or two before deciding which to keep in the system (likely the S20 as I suspect it will be easier on valves, plus is a bit more practical size wise in the available space). The thing I was very relieved about is they do sound like a pair, I wasn’t thinking one channel was stronger at all. Image very nicely centred with a very accurate Audio Synthesis dual mono stepped attenuator.

Are you going to try them with the Tannoys?

I will do in time certainly, and they will sound great, but I can’t see them ending up in that system due to input gain and general incompatibility with my Verdier valve pre (which I really like a lot). I also like to keep the main system compatible for drunken socialising, background running etc, e.g. I’ll have it on whilst I’m cleaning a huge stack of vinyl, when folk pop round for a curry, wine etc. I like the simplicity and absolute reliability of a simple fairly modern valve preamp and solid state power there. It is actually a very practical system. The Verdier/303 is a very good combo to my ears. The upstairs system is very different in that I pop up there for an hour or two of really critical listening, often lights out, and running a nice valve power makes sense there.

There is still a lot I want to understand with regards to reliability etc. I’m still puzzled by Leak’s decision to stick over 350V into the EL84s and what that means for tube life. My implication of the later resistor and cap mods which should prevent ‘run-away’ and hopefully avoid magic smoke, but I still don’t know what it means long-term. I also don’t understand the significance of the differing ‘ultra linear’ taps on the output transformers (IIRC 43% in the 3901s and 25% in the 8778s) and what implications that has on valve life? By saying all this there are some guitar amps, e.g. some Peaveys, that run their EL84s at an even higher voltage and don’t have a reputation of being tube-eaters. I also get the impression from reading hi-fi forums that once properly sorted all these Leaks are nice and reliable. The problems seem to occur on part-refurbished amps with some out of spec resistors and capacitors, or ones people have attempted to alter without sufficient knowledge. All my stuff is freshly done to standard values and with top quality components so should hopefully be stable. I think I’ll stick to 6P14P-EVs though as they are more robust/higher tolerance than an EL84 being far closer to a 7189.

I’ll be taking the multimeter to the Stereo 20 when I put that back in as I’m very curious as to what it is running its EL84s at. I’m still in some doubt which mains transformer it has, though it definitely has the 8778 outputs and was as far as I can tell shipped from Leak with the 470K grid resistors and 0.1uF caps. When it actually comes to it I suspect I’ll be running whichever looks to be the most economical amp(s) valve wise with the other stuck on a shelf as a spare. My impression so far is I don’t think there is much to call between them subjectively, though I hope to learn more tonight. The S20 has the advantage in that it has been butchered a bit so I can use nicer interconnects and it has better speaker connectors, though that will hopefully change as I asked Radford Revival if he’d make me some of plates he used so I can just swap-out the TL-12 plugs in a nice easily reversible manner.

 

[John_73]

They sound very decent. I wasn’t thinking “these are incredible” or “ugh, these are just terrible”, so I suspect they are pretty much on the level of the Stereo 20. Basically they sound really good. I’ll run them off and on for a week or two before deciding which to keep in the system (likely the S20 as I suspect it will be easier on valves, plus is a bit more practical size wise in the available space). The thing I was very relieved about is they do sound like a pair, I wasn’t thinking one channel was stronger at all. Image very nicely centred with a very accurate Audio Synthesis dual mono stepped attenuator.

It's nice to have the option to change systems around, particularly such mint examples as all your Leaks. Great to hear music from a similar time period through them too I imagine, especially when it's from a studio that may well have used Leaks in their monitoring systems. Unless circumstances change I'll never have the space for large speakers, so can only dream of how a pair would likely sound through your Tannoys - bet it'll sound incredible though! Naturally, we'll all expect some moody and stylish shots of these 'new' Leaks doing their thang taken in low light when you get the chance!

 

[Woodface]

Great thread this & top work from Tony.

 

[Tony L]

It's nice to have the option to change systems around, particularly such mint examples as all your Leaks.

It might be a personality type thing, maybe an ex-IT manager thing, but I do always like to have two of the things I really like so I’ve still got one if one needs to be fixed or whatever. It is no accident I have two 303s etc (both actually in use at present). As such having two variations on the Stereo 20 theme is fine. I can’t see my moving either ‘my’ S20 or the TL12 Plus on until proper retirement age. I do plan to flip the grey S20 though, but I have someone potentially interested there. It also hopefully means they’ll last a lot longer if I swap them over now and again for a change. Each can keep it’s own distinct tube-set(s), e.g. I’ll keep the fabulous’64 Mullard EL84s in the S20 as I suspect they’ll last longer there.

Naturally, we'll all expect some moody and stylish shots of these 'new' Leaks doing their thang taken in low light when you get the chance!

That’s the best I can do with the iPad and not moving from the listening seat! They’ve been on for a good hour now and seem to be behaving fine so far. Currently playing Sufjan Steven’s The Ascension, which some would view as being out of the comfort zone of vintage valves and LS3/5As, but it sounds superb! Amazing album whatever you play it on. They are very good amps for sure. Another one of those audio products that make you question how much real progress has been made in 60+ years!

 

[John_73]

Looks fab! Very envious!

Will check out The Ascension.

 

[Tony L]

Just completed a full two hours listening without any issue, that will do fine for day 1. Looking ok so far!

 

[George J]

Dear Tony,

"Bravo!!!!"

I am so pleased to read this thread.

If I ever get a Leak TL 12 Plus [or less likely 12.1], I am gratified to think that it will drive my ESL "to the Manor born.... "

Please forgive that that I am also envious of your success! In the most positive way imaginable of course!

Best wishes from George

 

[Mike P]

Well done Tony, they look great!

Another one of those audio products that make you question how much real progress has been made in 60+ years!

Doesn't it just. My system is now almost completely classic. Even my CD transport and DAC are 30+ years old!

I know you've got your reasons but....if it were me, I'd swap the 303 over to the upstairs system and move the Leaks downstairs onto the Tannoys. My Ardens really do sound great with both my ST20 and STA25.

 

[Tony L]

I found something interesting over on AudioKarma here about plate and grid voltage, which implies it can have little do do with valve life, it all depends on design, current etc.

What I’m trying to do here, though annoyingly don’t have anything even remotely approaching the necessary levels of education, is to try and understand, even in very broad brushstrokes, the thought process and practical effect of Leak’s resistor, capacitor and transformer (output and mains) changes during the life of both their EL84 amps. I get the impression there was a failure mode on the early amps that could lead to a ‘runaway’ situation where something started leaking, the leak caused more heat/current draw, which in turn increased the voltage leak or whatever. This seems to have dramatically escalated the demise of part-worn valves. I get the impression that the 470K and 0.1uF changes fix this and prevent the runaway, but I’d still like to better understand it and document more of the whole context on this thread.

I suspect a substantial part of it was for marketing reasons as the TL12 Plus needed to be a 12 Watt amp with 0.1% distortion as it was the intended replacement for the earlier and far more expensive TL12.1. As such they likely tried to get a good clean 12 Watts out of what is really a 10 Watt amp (the Stereo 20 only ever ever aimed for 10 a side). I guess with the resistor and cap modifications I’ve pulled my TL12 Plus down to 10 Watts, but I still don’t understand the significance of the output transformer change at all. Was that an attempt to get the full 12 Watts output back after the safety mod? By saying that the Stereo 20 went through the same changes but never had the requirement of delivering 12 Watts, so really I have no idea here!

 

[John_73]

It might be a personality type thing, maybe an ex-IT manager thing, but I do always like to have two of the things I really like so I’ve still got one if one needs to be fixed or whatever. It is no accident I have two 303s etc (both actually in use at present). As such having two variations on the Stereo 20 theme is fine. I can’t see my moving either ‘my’ S20 or the TL12 Plus on until proper retirement age. I do plan to flip the grey S20 though, but I have someone potentially interested there. It also hopefully means they’ll last a lot longer if I swap them over now and again for a change. Each can keep it’s own distinct tube-set(s), e.g. I’ll keep the fabulous’64 Mullard EL84s in the S20 as I suspect they’ll last longer there.

I understand that mind-set. I’ve done this in the past though it can get pricey and I haven’t the space currently for two of everything (or at least the items I’d want ‘backed up’). I do try and forward plan since I know how mercurial & fickle my taste can be! I’ve nearly got a complete set of carbon comps now for my Stereo 20 project, incase ‘future me’ suddenly has an attack of guilt for using modern resistors in a vintage amp! I can’t see this happening but it’s nice to keep the options open.

Interesting what you say about how the Leaks run their valves. I guess what one can take from their designs is that thousands are still running with the same set of valves. I think the Quad IIs run theirs harder, and I had a couple of unfortunate incidents with GECs red-plating back when I had my second pair of IIs, and they’d been fully rebuilt no expense spared. I was told the output valves benefitted from good matching for reliability. Going to a matched pair of modern Gold Lions I had no issues. I think the Leaks are easier on their valves and I don’t believe they need matched quads, though I’ll likely order a quad of those 6P14P-EV valves before risking the original ‘67 set of Mullards.

 

[Tony L]

I understand that mind-set. I’ve done this in the past though it can get pricey and I haven’t the space currently for two of everything (or at least the items I’d want ‘backed up’).

For me it is just space. At this point in time it makes more sense to keep really nice examples of classic audio as investments as they are still appreciating. I do like being able to swap things around now and again too, so it’s all good fun. Some is just investment though, e.g. I’ll never need more than one 3009, yet I have four!

Interesting what you say about how the Leaks run their valves. I guess what one can take from their designs is that thousands are still running with the same set of valves.

Take everything I say here with a huge pinch of salt! I’m bright enough to realise I know absolutely nothing of value about this and really I’m just using the thread as a sounding board in the hope I can learn from others far more knowledgeable.

The 6P14P-EV are very good and have proven very reliable so far in the Stereo 20. I’m currently running the ‘64 Mullards in that amp as the penny dropped early-pandemic last year that being around as long as I’d hoped is not guaranteed, plus my ears will never be as good in the future as they are right now anyway, so I may as well run the good stuff and enjoy them. I trust my S20 not to burn through them too fast. Once I’ve got 50-100 hours or so on the TL12 Plus and retested the 6P14P-EVs I’ll try the Mullards there too. They are a little warmer and more ‘3d’ than the Russian valves, though to be honest it isn’t a night and day difference.

As your Stereo 20 is a grey one it will have the 280V transformer and the later output transformers I guess it should be the kindest to EL84s of any Leak amp, so once you are confident the build is solid I’d happily stick the Mullards in it.

One thing I’m curious about with the TL12 Plus vs. Stereo 20 thing is whether it is ‘cheaper’ from a running cost perspective to run two GZ34s in the former more gently or one rather harder in the latter? The Mullard GZ34 is the most spendy tube here. It seems you are looking at >£100 for a NOS or even good used one these days. I’m lucky to have five of them, three later ones being of the same era and design, so some degree of redundancy there for the TL12s.

 

[Barrymagrec]

The GZ34 is already comfortably under run in the Stereo 20 so I doubt you would double it`s life in the TL12+.

They could quite happily used a EZ81 in the TL12+ and still been very comfortably under the ratings.

 

[Tony L]

I think I have the original GZ34 for my Stereo 20, a fat-base Mullard with an appropriate date-stamp, and it still works fine. My little Orange valve-tester can’t do rectifiers (or EF86s), which is a shame. There was a similar fat-base Mullard GZ34 in TL12 Plus #1 when I landed it at the auction, though annoyingly it had leaked and the getter was white. The two Mullard EL84s and ECC81 all tested good and the EF86 seems fine too, so a real shame about that GZ34!

 

[snowman_al]

First, I'm glad it is all working now. You have done a tidy job.

... What I’m trying to do here, though annoyingly don’t have anything even remotely approaching the necessary levels of education, is to try and understand, even in very broad brushstrokes, the thought process and practical effect of Leak’s resistor, capacitor and transformer (output and mains) changes during the life of both their EL84 amps. I get the impression there was a failure mode on the early amps that could lead to a ‘runaway’ situation where something started leaking, the leak caused more heat/current draw, which in turn increased the voltage leak or whatever. This seems to have dramatically escalated the demise of part-worn valves. I get the impression that the 470K and 0.1uF changes fix this and prevent the runaway, but I’d still like to better understand it and document more of the whole context on this thread.

I suspect a substantial part of it was for marketing reasons as the TL12 Plus needed to be a 12 Watt amp with 0.1% distortion as it was the intended replacement for the earlier and far more expensive TL12.1. As such they likely tried to get a good clean 12 Watts out of what is really a 10 Watt amp (the Stereo 20 only ever ever aimed for 10 a side). I guess with the resistor and cap modifications I’ve pulled my TL12 Plus down to 10 Watts, but I still don’t understand the significance of the output transformer change at all. Was that an attempt to get the full 12 Watts output back after the safety mod? By saying that the Stereo 20 went through the same changes but never had the requirement of delivering 12 Watts, so really I have no idea here!

Very broad brush, the humble EL84 was designed to dissipate a total of 14 watts. After that the valve will run hotter and eventually the internal parts run beyond their safe range. The grid 1 (the one attached to ground by the 1MΩ R16/17) then can start to emit electrons, like the cathode, which turns the valve on more and increases the dissipation even more. That is the vicious circle or thermal runaway. Something has to fail, the EL84 'melts' then the cathode resistor cooks as it cannot carry the extra current, often the bypass cap pops as its voltage is exceeded, the 100Ω resistor gets very hot and the mains transformer starts to melt its wax, if you are very unlucky it or the output transformer cannot handle the excess current and will fail like a fuse...
So the original TL12+ runs the EL84s at 15+ watts. (Using ohms law, current through the valve is calculated by dividing the cathode voltage 12.5 volts by the resistance 270Ω = 0.046A or 46mA. The voltage through the valve is 350 volts HT minus the 12.5 cathode voltage = 337.5volts. Now watts are volts times current so 337.5 x 0.046 = 15.5 watts.) Some EL84s could take it many could not. Leak were pushing their luck.

Lowering the HT voltage reduces the dissipation of the EL84 and dropping the value of R16/17 to 470K 'bleeds' the active electrons forming on the Grid 1 to earth / ground, so helps prevent the valve being turned on harder.

Broad brush as I said. There are other factors in operation too, but no need to go there at the moment.

The 6P14P-EV is a better spec, close to the 7189 or EL84M. These have a maximum dissipation figure of about 17 watts (depends on the data sheet you use) so should cause little concern.

 

[snowman_al]

Part II,
(I some how dropped it off the first response...)

... I suspect a substantial part of it was for marketing reasons as the TL12 Plus needed to be a 12 Watt amp with 0.1% distortion as it was the intended replacement for the earlier and far more expensive TL12.1. As such they likely tried to get a good clean 12 Watts out of what is really a 10 Watt amp (the Stereo 20 only ever ever aimed for 10 a side). I guess with the resistor and cap modifications I’ve pulled my TL12 Plus down to 10 Watts, but I still don’t understand the significance of the output transformer change at all. Was that an attempt to get the full 12 Watts output back after the safety mod? By saying that the Stereo 20 went through the same changes but never had the requirement of delivering 12 Watts, so really I have no idea here!

Tony,
Your amp will still deliver the same output power it did when it was first made. Changing the grid leaks and cap have no effect on output power.
When Leak lowered mains transformer voltage, and hence the HT voltage, there was a slight power loss, but the valves now operate within the design envelope and dissipation. To compensate for this and still meet the advertised power output Leak redesigned the output transformer. They moved the ultra linear tap from 50% (as in your 3921 transformers) to 25% (8778 transformers). That slightly raises the output power.
Think of it like this, If the tap was at 100% you have the EL84 as a Triode, the second grid is connected to the anode, like the TL12.1 has. That gives least power. If you connect the second grid to the HT supply that is full Pentode mode and gives most power.
Leaks are Ultra Linear so some where in between those 2. 43% is said to be ideal. So the closer the ultra linear tap to the centre tap of the transformer (lower percentage figure) the closer you get to Pentode operation, so more power. The trade off is more distortion.

I think the Stereo 20 is power limited by the mains transformer. It would need to be larger to keep the HT voltage up. If you see the HT voltage for the TL12+ with the 300 volt transformer the HT is 350/360 volts.
On the ST20 the 'same' 300 volt transformer only maintains 320/330 volts HT.