Leak TL/12 Plus / Point One Plus

[Barrymagrec]

I`d replace the black Hunts moulded caps as well, Tony they are notoriously bad.

 

[Tony L]

Here’s the Point One Stereo schematic:

I’ve flipped my photo so it is the same way up as the layout above:

I’m planning to do:

C17 x2 50uF 12V polarised (I’ve ordered some 47uF 25V axial)
C5 x2 50uF 12V polarised (as above)
C4 x2 0.1uF (I’ve already got some IC yellow film caps)
C21 8uF 450V polarised (I’ve already got an F&T 10uF)

That’s the red ones with the yellow labels, the black ones, and the big silver one.

There are a couple more of the black Hunts buried real deep on the back of the controls, but they can bugger right off! I’m not going in there unless I really have no alternative. That has to be low-voltage stuff, I can’t see it blowing anything up. I think I’m quite lucky with this example as it has a lot of Mullard mustard and polystyrene caps.

Obviously all the carbon resistors may have gone crazy, but I think changing the seven caps above should at least make it safe to power up. My main concern is it not hurting the TL12 Plus it will be powered from. I guess it makes sense to use the dim-bulb tester and stick to mono initially.

 

[Barrymagrec]

Hmm, too many EF86s for my liking, but that was the 50s for you.

There is a series resistor in the HT input so that should isolate the TL12 from any likely damage.

You can check most of the resistors in circuit, particularly if you have removed the bypass caps, which might be leaky.

 

[Tony L]

What don’t you like about the EF86? I’ve no issue with them so far, e.g. I don’t think the pair of TL12 Plus sounds any worse than a Stereo 20 despite swapping the ECC83s for an EF86 and ECC81. I’m not convinced they sound any better, though they may have a little more power (better PSU?). I know some guitarists (AC30s etc) think they are unreliable compared to ECC83s, but I’ve not found a noisy one yet. I’ve ended up with loads of them! Annoyingly my Orange tester can’t test them, but all I’ve tried (all ‘50s or ‘60s Mullards) work fine.

PS Better resolution of the Point One Stereo schematic here.

 

[Barrymagrec]

I have found EF86s to be quite variable and generally noisier than an ECC83, for instance. An EF86 in a Mullard 2 valve preamp was the first valve failure I ever experienced and it kind of put me off them. I think for reliability it`s predecessor the EF37A was better.

A single ECC83 stage (2 triodes) will give about the same gain at the cost of a couple of components and 50% more heater consumption, well worth it for the greater reliability and better performance.

When Leevers Rich changed their replay amp design from EF86s to ECC83`s the noise figure was improved by about 5dB which was quite significant.

 

[John_73]

Looks like the leaky PIO caps have all been replaced by the Mustard caps and quite a few of the carbon comp. resistors with carbon films. So should be much easier to get this good looking example up and running. FWIW - and rather like the Quad pre-amps - I was pleasantly surprised by how good my Varislope 2 Stereo sounded into my Stereo 20, after reading for decades how bad the pre-amps where. Yes they're not up to the standards of some pricey Khozmo pot in a box job, but very pleasant to listen to and just draws you into the music. Look forward to seeing your progress Tony. My Varislope 2 Stereo is in pieces at present awaiting similar resurrection. The real fiends are the carbon comp. resistors in the switching banks and tone controls I've taken those off to make replacement far easier. I suspect (few both replace them as they're a pig to get to) it's those responsible for much of the noise in unrestored Varislopes.

 

[Tony L]

Interesting, it hadn’t occurred to me it may have previously been worked on aside from one specific resistor looks different left to right. I assumed the mustard caps were right as I think they are period-correct and I have seen some in other Point One Stereos. I’ll go googling for more pics later.

To be honest I’ve no intention of doing a full strip and rebuild as I assume even if I liked it the gain staging would make it unusable with modern sources. I really don’t like the way it is powered by just one TL12 too, that asymmetry just triggers me. It would have to suck some PSU headroom from the left (powering) amp. I just want to get it to work safely, that is all. I can’t imagine not using my Audio Synthesis here.

PS One interesting thing is it may help us figure out when the Leak colour change from champagne to bronze came. The side and top panel metalwork of this Point One Stereo is bronze, not champagne like my older mono Point One and Varioslope preamps (these also have black knobs). This suggests the change was probably early to mid-1959. That would explain why champagne Stereo 20s are so crazy rare! Less than a year of them and at a time where stereo had only just been introduced and was still very unusual.

 

[Barrymagrec]

The power consumption even of a stereo preamp is minimal compared with the TL12 - the imbalance is just not something to worry about.

I don`t think mustards came out until the sixties so probably the exact build changed over time.

 

[Tony L]

Yes, after looking around a bit on Google I agree this pre has been pretty extensively reworked. The ones I saw with mustard caps had been restored on foreign language sites.

I guess I need to go round and double-check everything is the correct value now! In most respects it is nice that it has been done as it saves expense and Mullard mustard caps are good and very far from cheap, but I’d have done it a lot neater looking at the picture more closely, e.g. all the resistors the same way up, caps with the values visible, everything aligned height-wise etc! I don’t know why I didn’t spot that as Leak’s work was always flawless, just stunningly good. I’ll leave it be, but I will try beeping stuff out to check values (my colour sense/ability is not up to reading resistor bands, but I can usually tell if a pair are the same or not).

PS Why they didn’t do the red/black/yellow Plessey caps is beyond me, they are famously bad!

 

[John_73]

Perhaps the work was done mid/late 70s, so the Plessey caps may well have been fine at that point. The replacement parts all look vintage.

 

[John_73]

I really don’t like the way it is powered by just one TL12 too, that asymmetry just triggers me. It would have to suck some PSU headroom from the left (powering) amp. I just want to get it to work safely, that is all. I can’t imagine not using my Audio Synthesis here.

Was the same with the Quad IIs and Quad 22. I was similarly triggered by it, but after restoring both could honestly not hear any channel matching issues whatsoever. I imagine it’ll be the same with your Leaks.

 

[Barrymagrec]

Was the same with the Quad IIs and Quad 22. I was similarly triggered by it, but after restoring both could honestly not hear any channel matching issues whatsoever. I imagine it’ll be the same with your Leaks.

I think with the Quad the tuner was also driven by only one amplifier and that would take a lot more power than a preamp.

 

[Tony L]

Perhaps the work was done mid/late 70s, so the Plessey caps may well have been fine at that point. The replacement parts all look vintage.

I have a feeling the work may have been done earlier than that as the EF84s have obviously been changed and date from around the mid-60s. I can’t see any obvious evidence that it blew up, but the amp it was connected may have. It is puzzling as I’d not have expected anyone to burn through ‘50s Mullard EF86s so soon, the ones that came with my TL12 Plus and in both mono preamps are all fine based on a listening test in the TL12s (I can’t test them otherwise).

I associate Mullard mustard caps with rare early ‘60s guitar amps from Vox, Marshall etc. Google says they were introduced in 1958, so period correct with the Leak. They are one of those things that if you see in an amp you know are not to be replaced. They seem long-term stable (unlike say the similarly sought-after ’bumble bees’) and the guitar geeks love them. This is why I just assumed this pre was stock without noticing the work was a little janky and certainly not up to Leak standards. I don’t know enough about resistors to date those, but as you say they may be ‘70s. Whenever it was done whoever did it might have deliberately used nice vintage Mustard caps. Regardless assuming the values are correct I’ll take it as a win as they alone are worth more than I paid for the whole pre (£30!).

 

[Woodface]

It looks very pretty

 

[John_73]

I have a feeling the work may have been done earlier than that as the EF84s have obviously been changed and date from around the mid-60s. I can’t see any obvious evidence that it blew up, but the amp it was connected may have. It is puzzling as I’d not have expected anyone to burn through ‘50s Mullard EF86s so soon, the ones that came with my TL12 Plus and in both mono preamps are all fine based on a listening test in the TL12s (I can’t test them otherwise).

I associate Mullard mustard caps with rare early ‘60s guitar amps from Vox, Marshall etc. Google says they were introduced in 1958, so period correct with the Leak. They are one of those things that if you see in an amp you know are not to be replaced. They seem long-term stable (unlike say the similarly sought-after ’bumble bees’) and the guitar geeks love them. This is why I just assumed this pre was stock without noticing the work was a little janky and certainly not up to Leak standards. I don’t know enough about resistors to date those, but as you say they may be ‘70s. Whenever it was done whoever did it might have deliberately used nice vintage Mustard caps. Regardless assuming the values are correct I’ll take it as a win as they alone are worth more than I paid for the whole pre (£30!).

It’s always fun trying to piece together the rough history of a vintage piece of kit. There’s always the possibility it was a tweaker, and there was nothing wrong with the unit prior to the changes. I have no idea what the tweaky ‘must do’ zeitgeist was at the time, if indeed there was one. But as you say, those Mustard caps where and still remain highly regarded, not to mention extremely reliable. And replacing the carbon comps with quieter carbon films was likely quite an effective upgrade back when, as now. Perhaps whoever did the work was trying to get a quieter pre-amp. Funnily enough my Stereo 20 had had its 0.25uF caps replaced with Mullard mustard caps, though the work was to a far shoddier standard than your pre.

 

[Tony L]

One thing I noticed when cleaning up the Point One Stereo is that it isn’t just a stereo version of a Point One Plus. Sadly it lost the different phono eq curves, which is a rather interesting feature of the Point One Plus and would certainly make it a very good candidate should one wish to play 78s etc. I’d like to hear really early ALPs, LXTs etc through it as I’ve never tried anything other than RIAA eq.

PS Still waiting on capacitors to land for the Stereo. I’ve not taken a soldering iron to it yet.

PPS There is a slight temptation to find another identical Point One Plus and try full dual mono!

 

[Tony L]

The more janky caps now replaced. The red/black Plessey ones with yellow labels and the black Hunts don’t measure as capacitors anymore. The silver 8uF was actually ok and beeped appropriately on my ESR meter.

As I understand it that’s got everything that could present an electrical risk out of the way so I’ll try it out sometime later and see if it works. There are a few other Hunts caps in there stuck to the input selector, and rumble filter, but I’m pretty sure they are low voltage (maybe passive) EQ etc. I’m a little concerned that it has had work done previously, but I haven’t anything obvious wrong or modified.

 

[Tony L]

It actually works! No fire or anything! Controls are a bit crackly, there is some hum, and the balance control does the opposite of what I’d expect, but that aside it works and sounds surprisingly respectable.

I’d previously set the level controls on the back to what I assumed was about the middle of their travel and it is actually very usable on a typical modern CD input, which surprised me. I was expecting it to behave like a valve fuzz box when presented with a 2V line input, but no, it is very usable, and given I’d set the gain knobs in their mid position further cut would be possible. Where it is now is fine though, about ‘ten o’clock’ for a typical listening level.

I’ll try cleaning the controls later, I’d previously only given them a bit of a workout, I’ve not used any Deoxit yet. I suspect they’ll clean up. I need to give the valve bases a better clean too as they are noisy when jiggled.

The hum is kind of expected. The manual mentions it and suggests lifting the earth on the amp the preamp isn’t connected to, but that’s a step too far for me. My goal here was just to find them their preamp and fix it, not really to use it day to day. The Audio Synthesis makes more sense.

I don’t understand the balance control though. I’ve double-checked everything and the octal lead is going to the left amp, the other plugged into the ‘Output R’ RCA plug on the rear. Speaker leads are to the correct amps etc. Very odd.

 

[Tony L]

…looking at the facia of the Leak (pictured upthread) is the balance control subtractive? It is actually labelled -L, -R, and the tone controls do have +/- markings. If so it’s just really odd, not wrong or broken! I guess it is very, very early days of stereo so this stuff wasn’t fully nailed down yet.

 

[Barrymagrec]

It does look as if it was intended to be like that.

It would be a simple job to reverse the pot wiring to work normally - but then it wouldn`t be original.....