leak stereo 20 restoration

[simon e]

Hi all,

I'm about to start restoring my st20, and may be look at lowering the input sensitivity.

So if anybody has any advice about type and brand for caps and resistors to use in the various parts of the circuit that would be great.

There is a lot of information floating around on the web but it would be great to get advice from anybody who has done this before.

Thanks
Simon

[walpurgis]

Hello Simon, I've owned several Stereo Twenty amps and I'd be inclined not to deviate from standard component values. If you have an input oversensitivity situation, you could try a pre-amp with adjustable or lower output, or maybe some in-line attenuation like the Rothwell attenuators. I've got these and they work well and seem to have no noticeable negative impact on the sound. Regards, Walpurgis (Geoff).

[jaym481]

I use a Rothwell passive "preamp" with my Stereo 50. Just keep the cable capacitance between the amp and the "pre" low, and it works very well. I tried the Rothwell attenuator plugs with my active preamp, and found the combination dulled things somewhat, and they didn't attenuate enough for the gain of my pre.

[IHP]

Hi Simon,

I've no technical knowledge so can't assist with component values but I would say that the Russian PIO caps that Paul @ Classique Sounds sells are in my 20 and it sounds amazing.

http://www.ebay.co.uk/itm/Leak-Stereo-20-Paper-oil-capacitor-pack-/270948729215?pt=UK_AudioTVElectronics_HomeAudioHiF i_Amplifiers&hash=item3f15cd817f#ht_2247wt_1344

[simon e]

Thanks all, for all of the replies, I think I'll leave the circuit alone on the leak and concentrate on replacing the 40 year old components.
Has anyone used hifi colective for spares?
or know any good 32uF 400V double electrolytic smoothing capacitors?

[Reid Malenfant]

See if you can find something to suit out of this lot :)

http://www.ebay.co.uk/sch/i.html?_kw=capacitor&_kw=32uf&_dmpt=UK_MusicalInstr_Amplifiers_RL

[anthonyTD]

hi Simon,
There are a few ways you can reduce the gain on the front end of the Stereo 20, the easiest being, changing the first double triode for a lower gain version ie; ECC81 [gain of around 55] ECC82 [gain of around 22 ] or a 5751 [gain of around 70] but each of these valves will have a sonic impact on the amp, so a bit of experimenting would need to be done.some other [more drastic] measures are, removing the cathode bypass cap from the first Triode Stage, or reducing the plate load resistor on the first triode from 100k to around 47k.
Hope this helps.
Anthony,TD...

[simon e]

hi Simon,
There are a few ways you can reduce the gain on the front end of the Stereo 20, the easiest being, changing the first double triode for a lower gain version ie; ECC81 [gain of around 55] ECC82 [gain of around 22 ] or a 5751 [gain of around 70] but each of these valves will have a sonic impact on the amp, so a bit of experimenting would need to be done.some other [more drastic] measures are, removing the cathode bypass cap from the first Triode Stage, or reducing the plate load resistor on the first triode from 100k to around 47k.
Hope this helps.
Anthony,TD...

Hi Anthony,

I had read about changing out the ECC81, I may have a play with this as I think the amp will need a new set of valves as I believe they are all original Mullards, I need to find someone in Dublin with a valve tester so I can see exactly what state they are in.

[simon e]

See if you can find something to suit out of this lot :)

http://www.ebay.co.uk/sch/i.html?_kw=capacitor&_kw=32uf&_dmpt=UK_MusicalInstr_Amplifiers_RL

Hi Reid,

Thanks for the link. I think I might try some of these:http://www.hificollective.co.uk/components/mcap_mlytic_hv.html

just need to check they'll fit without having to alter the leak chassis :scratch:

[anthonyTD]

Hi Anthony,

I had read about changing out the ECC81, I may have a play with this as I think the amp will need a new set of valves as I believe they are all original Mullards, I need to find someone in Dublin with a valve tester so I can see exactly what state they are in.
Hi Simon,
just to be clear, there should be an ECC83/12AX7 fitted in the front end as standard, my sugestion would be to substitute this for an ECC81, or 5751, or even an ECC82, however, with an ECC82 i am not sure you will get enough gain from the first stage to drive the rest of the chain to full output [its a while since i have played with one of these] my first sugestion would be to fit either an ECC81, [CV4024] or 5751, and disconect the first cathode bypass cap to lower the gain, and see where you are then.
Anthony,TD...

[DSJR]

Sorry to butt in, but hifi dave's Stereo 20 only looks to have had basic cap changes (the rest looks surprisingly original but I could be wrong here). The gain is fine with the Croft preamp - and we should all remember the questions about cramped volume controls at the bottom a while back.

[anthonyTD]

Sorry to butt in, but hifi dave's Stereo 20 only looks to have had basic cap changes (the rest looks surprisingly original but I could be wrong here). The gain is fine with the Croft preamp - and we should all remember the questions about cramped volume controls at the bottom a while back.
Hi Dave,
first of all, welcome back, now unfortunetly i am not sure i understand where your coming from, please explain.
A...

[simon e]

Sorry to butt in, but hifi dave's Stereo 20 only looks to have had basic cap changes (the rest looks surprisingly original but I could be wrong here). The gain is fine with the Croft preamp - and we should all remember the questions about cramped volume controls at the bottom a while back.

Hi Dave, thanks for the reply, I don't want to get to hung up on modding the leak, st this point. I want to concentrate on replacing the aging components. And making sure I pick the right replacement parts as I know this could have a big effect on the way this amp sounds.

[anthonyTD]

Hi Simon,
I have rebuilt lots of these amps over the years and i would agree with others here, if the resistors are tested and still in tolerance and not found to be noisey i would be inclined to leave them, however, i would replace all power supply, and bypass caps, also, all coupling capacitors.
There are a few type of caps that can be used which will improve the amp, however, i feel it will be down to personal choice and the recomendations of others who use this amp in a similar situation and set up.
Anthony,TD...

[simon e]

Hi anthony,

What do you mean by noisey resistors?

[anthonyTD]

Hi anthony,

What do you mean by noisey resistors?
Hi Simon,
Carbon resistors can become noisey over time in that they can make intermitent crackling, and hissing type noises, it can be difficult to know which ones are causing these noises, however, the ones in the plate/anodes should be suspect first.
Valves can also cause similar noises so be sure if you have these types of sounds that its not the valves first.
Anthony,TD...

[simon e]

Thanks Anthony,
That makes sense, I've had the odd crackle, but I think that's been caused by a dirty contact on one of the valves.

[simon e]

Well I think its about time to update this thread. After lots of reading and talking to people on the leak forum I've gone and bought all the bits to restore my st 20.

PIO Russian capacitor kit from eBay.
Mundorf smoothing capacitors + an additional 100uf capacitor.
And a mixture to Takman and Kiwame resistors.

Just started by replacing the smoothing capacitors this evening which fit nicely in the original holes. And well it curtainly doesn't sound any worse.

I'll update with some pictures over the weekend.

[Wilbur]

JUst got a Stereo 20/pre amp
Did you make any more progress??

[simon e]

Still making slow progress replacing all the capacitors and resistors. The new power supply capacitors have made a real improvement to the bottom end.

Hope to have some time over Christmas to get the soldering iron out.

Sent from my Nexus 7 using Tapatalk 2

[6L6]

I am quite interested in your progress, Leak kit is quite rare on this side of the pond.

Please post some photos if you get the chance! :D :D :D

[simon e]

Ok time for a quick update, managed to sit down with the soldering iron the other evening and replace a few more of the capacitors on the leak and add an extra 100uF cap to power supply capacitors which is a recommendation from the Leak forum.

Its sounding very good, still a bit of a hum with no input, so need to try and trace that, but I still have a lot of capacitors to replace. but the extra 100uf on the supply seems to have really improved the bass.

http://i1191.photobucket.com/albums/z462/s_ewings/37ee566a-9bbb-4a72-8b1f-e4b6e23da50f.jpg

http://i1191.photobucket.com/albums/z462/s_ewings/cc0c68a6-bfe2-47fc-ba51-a2a99801773f.jpg

[Rare Bird]

Looks like you might have changed the 100 Ohm/3watt resistor that protects the mains transformer. Be sure to keep it three watts & make sure it can easily desolder itself if over current happens. It designed to do this.. 'Stereo 20's are one of my fav 'EL84' amps.. :) i love's the Lafayette 'LA 310' too :eyebrows:

[simon e]

Looks like you might have changed the 100 Ohm/3watt resistor that protects the mains transformer. Be sure to keep it three watts & make sure it can easily desolder itself if over current happens. It designed to do this.. 'Stereo 20's are one of my fav 'EL84' amps.. :) i love's the Lafayette 'LA 310' too :eyebrows:

The 100 Ohm/3watt resistor is still intact. Although it may have been changed in the past.

Sent from my Nexus 7 using Tapatalk HD

[Jonboy]

i love's the Lafayette 'LA 310' too :eyebrows:


Me too, your still not having it :lol:

[Rare Bird]

:eyebrows: