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Leak Stereo 20

I can confirm that the supplier of the baseplates and the ST20 are the same Steve.
He's putting out these ones at below cost price to test the market so buy one now and get a bargain.
The PCB's did indeed come from E.A .,
but there is no other tie up otherwise.
The output transformers are wound exactly as the originals, the only difference being the Iron being of higher quality so resulting in even better bass response, not that the originals were lacking in any way.
I believe there is a 16 Ohm tap available but is not actually used in the current version as would make the switching a bit complicated, (I suspect you could order one to be done with 16 ohm output).
I also believe that he is in negotiations with IAG as they asked him to build the amps for them. They want a product that is 100% UK built.
 
John_73 said:
Just saw this over at Lenco Heaven. Seems like the English Acoustics chap holds the rights to the Radford brand?

https://www.lencoheaven.net/forum/index.php?PHPSESSID=oot35aaabqar74v04ooc607g43&topic=38546.15
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Well, he says that he has "access" to the rights. What rights access that it is is not clear. He may not have the right to use the Radford designs in order to build something and sell it, but maybe just to view and learn from. IPR is a tricky subject twisted with careful wording.
 
The stereo 20 has 4, 8 and 16 ohm taps. I have a pair of 4 ohm speakers and am pretty sure they sound better of the 8 ohm tap.

Will using the amplifier in this manner cause any damage?

Also, any idea which tap one should use for a headphone tap?

Cheers
 
foxwelljsly said:
Will using the amplifier in this manner cause any damage?
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No, it won’t cause damage. Speakers are far from a constant impedance anyway so it can only ever be a compromise. As ever if it sounds better it is better!

It is useful to find an impedance plot for the speaker in question, e.g. here’s one for the JR149s:

8710147828_dd742b1969_c.jpg


Typically far from flat, but nothing below 8 Ohms. It is no surprise they favour the 16 Ohm tap.

foxwelljsly said:
Also, any idea which tap one should use for a headphone tap?
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I’d have thought the 16 Ohm tap as headphones tend to be 32 Ohms and upwards. Very efficient too, so you likely need to stick some pretty chunky resistors in line somewhere. The ‘Can Opener’ box I have is designed in this way. I’d certainly not just plug them straight onto the outputs. The gain/level is all wrong.
 
Tony L said:
No, it won’t cause damage. Speakers are far from a constant impedance anyway so it can only ever be a compromise. As ever if it sounds better it is better!

It is useful to find an impedance plot for the speaker in question, e.g. here’s one for the JR149s:

8710147828_dd742b1969_c.jpg


Typically far from flat, but nothing below 8 Ohms. It is no surprise they favour the 16 Ohm tap.



I’d have thought the 16 Ohm tap as headphones tend to be 32 Ohms and upwards. Very efficient too, so you likely need to stick some pretty chunky resistors in line somewhere. The ‘Can Opener’ box I have is designed in this way. I’d certainly not just plug them straight onto the outputs. The gain/level is all wrong.
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Cheers, as I thought.

I have Kef 104.2's, which use conjugate load matching and should present a constant load almost identical to a 4 ohm resistor. The speaker switching unit I use has a similar resistor network to the can opener off it's couple of sockets. The big 80's Kefs might not be the obvious choice with the Stereo 20, but the combination sounds magical and at 4r and 92dB go plenty loud enough.
 
A while back I’m sure somebody here was advising that the four 270R cathode resistors (R14, R15 per channel) in the Stereo 20 should not be more than 1W, and carbon film, to act as an additional safety net should a valve go down.

Whilst I remain delighted with my Stereo 20, I’ve currently got x4 Mills 5W wirewounds fitted in these positions. Should I ideally be replacing these with 1W carbon films?

Ta.
 
I’m in the same position and tempted to do the same to my TL12 Plus. I spent ages googling this a long time back and couldn’t find any consensus view.

PS There is another factor too in that modern resistors can’t handle the high voltage, e.g. a 1W modern metal film would fail in that position. Using a higher Wattage effectively increases the voltage headroom. It is confusing and I’d really like a definitive answer here, e.g. a recommendation of a specific resistor brand and Wattage to use.
 
I do periodically do an Ebay search for Stereo 20s just to see what others have done to theirs, and it’s not uncommon to see modern carbon films in those positions, but looking a little toasty already.

My current opinion, particularly as I’m using the reliable K40Y-9 Russian PIOs and new 6P14P-ER output valves, is to leave the Mills in there. I think if I was using untested output valves I might then be inclined to change to 1W carbon films.

But would be useful to have some concrete advice for these positions, both for the Stereo 20 and your TL12+.
 
I have no knowledge of how often this is a problem but my feeling is that attempting to use the cathode resistor as a fuse will mean running it near it`s rating, leading to reduced reliability.

Voltage rating of resistors is often overlooked but in this case, with only about 10 volts it`s not an issue.

It would be possible to design and fit an over voltage sensor for each of the cathodes that would shut off the power if any of the output valves exceeded their nominal current by more than a certain amount and it could be made easily removable in order to revert to original factory standard.
 
John_73 said:
But would be useful to have some concrete advice for these positions, both for the Stereo 20 and your TL12+.
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I’m running the same 6P14P-ER valves (tested fairly regularly) and K40Y-9 caps in my TL12 Plus. I’m also running with 1A fuses, the Leak spec is for 2A.

PS HiFi Collective have 270 Ohm Takman carbon film in 1W and Kiwame in 2W.
 
Tony L said:
I’m running the same 6P14P-ER valves (tested fairly regularly) and K40Y-9 caps in my TL12 Plus. I’m also running with 1A fuses, the Leak spec is for 2A.

PS HiFi Collective have 270 Ohm Takman carbon film in 1W and Kiwame in 2W.
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Seriously impressed with those 6P14P-ER valves. I may even prefer them just slightly to the Mullards. An absolute steal at the price and should last for decades yet. About to order a 2nd set to keep as a standby. I suspect these will shoot up in price too as stocks eventually lesson.

Must admit in no rush to change those resistors unless someone offers concrete evidence why one should, but might order the Takmans anyway to store. I was rather OCD about soldering in all the components just-so, and having to remove those four and do it all over again will be a bit of a faff.
 
John_73 said:
Seriously impressed with those 6P14P-ER valves. I may even prefer them just slightly to the Mullards.
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Likewise. I have what I strongly suspect was (before I ran them) a NOS set of yellow print ‘65 Mullards and on balance I prefer the 6P14P-ER valves. They seem more punchy and controlled if at the price of a little brightness. Thankfully I stockpiled them back when they were cheap so hopefully have a lifetime supply. I’ve got two unused quads, two used/good quads, and the set currently in the amp. I find the different varieties somewhat baffling, I’ve got at least two types, one having gold pins, the other not. I think some are the 10,000 hour variety, the others 5000 hour, though I’m not exactly sure which is which!

I’ve certainly got a lot of EL84s! There’s another five Mullards in the stash too, but not a matched quad (two early with square getters, two Holland made, and one which would keep the NOS quad running longer as it is the same type/close date). All test good on the Orange.

John_73 said:
Must admit in no rush to change those resistors unless someone offers concrete evidence why one should, but might order the Takmans anyway to store. I was rather OCD about soldering in all the components just-so, and having to remove those four and do it all over again will be a bit of a faff.
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Likewise. Thankfully they are real easy to get to so swapping them is no real issue, but I’d want someone who really knows these amps to advise doing it and telling me exactly what resistors to use beforehand.

PS Talking about folk who really know these amps does anyone know what happened to @snowman_al? I have a nasty feeling he is no longer with us (I knew he was very ill), but I have no confirmation of that. His endless help and patience with my TL12 Plus rebuild was invaluable. Those amps owe him big!
 
Where those the Mullards you were lucky enough to get when you found the NOS grey Stereo 20? That was quite the find!

Alas my Mullard EL84s that were original to my Stereo 20 are well used, with one pretty much past it (the left channel had a meltdown at some point when my Uncle owned it). I did buy a date appropriate Mullard spare, but to be honest haven’t tried them since getting the 6P14P-ER set. I love the construction consistency of them too, all the innards face in the same direction! Soothes my OCD no end haha! Do have a Harma set too - not sure what the actual make is, but they sounded rather boring compared to both the Mullards and the 6P14P-ERs.

I think the 6P14P-ER (looks like EP in cyrillic) are the military spec 10,000+ hour versions (mine don’t have the gold plated pins, so some variability there), with thicker mica supports and gold plated grid. Not sure of the EV are the ‘standard’ versions or even better than the ER?

Edit : https://www.jogis-roehrenbude.de/Russian/russ_roehre_rue_dat.pdf
 
Tony L said:
PS Talking about folk who really know these amps does anyone know what happened to @snowman_al? I have a nasty feeling he is no longer with us (I knew he was very ill), but I have no confirmation of that. His endless help and patience with my TL12 Plus rebuild was invaluable. Those amps owe him big!
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Oh no! I really hope that’s not the case. Will check over at the Vintage Radio repair forum, I think he used to post regularly there.

Edit : He hasn’t posted since August 2022 there.
 
The 270 Ohm resistors only have around 12 Volts on them so no problems with high voltage.
I always use either Iskra or Piher 1 Watt resistors there. Also helps they're nice an vintagy so look the part too.
 
John_73 said:
Where those the Mullards you were lucky enough to get when you found the NOS grey Stereo 20? That was quite the find!
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Yes, that’s the set. Got me a nice date-matched trio of ECC83s and a GZ34 too. Always useful! I’ve still got that amp sitting in its box, not sure what to do with it. I can’t see myself rebuilding it as I just don’t need it, but if I sold it it would certainly be without valves!
 
John_73 said:
Oh no! I really hope that’s not the case. Will check over at the Vintage Radio repair forum, I think he used to post regularly there.

Edit : He hasn’t posted since August 2022 there.
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I really hope he's OK. I always read his posts with great interest.
 
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