Author Topic: Leak Stereo 20 Modifications  (Read 24669 times)

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #20 on: September 08, 2014, 03:50:14 PM »
That Leak is beautifully re built Steve.  I would imagine it would sound really good with some Lowther horns or the like.
Interesting, I have at the insistence of a friend, tried it on my axiom 80s with very good results. Sweet, pretty, warm, involving, with a lot of liquid body. As for lowthers,  this amp will be a very good match for lowthers, because its strengths oppose the lowthers weaknesses.
« Last Edit: September 08, 2014, 03:52:53 PM by stevenvalve »

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #21 on: September 08, 2014, 03:59:29 PM »
I must say, the great thing about the Leak stereo 20, they are cheap to buy, the valves are cheap, the sound when set up correctly is just superb.

Offline zenelectro

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Re: Leak Stereo 20 Modifications
« Reply #22 on: September 08, 2014, 04:24:28 PM »
I have only dropped about 10 volts, using the 10 henry, 200ma, choke pictured above. I am changing chokes every week to find the right one.  A smaller choke will probably have less effect on the voltage, 2 henry will probably do, what works. As for wire, i have been trying different wire types, Cat 5 sounds very good, it has the great balance when added with the sound of the original leak wiring. And as with the choke all dramatically changes the sound.

Just measure the DC resistance across the choke with a multimeter. If it is say 100 ohms and you are running say 120mA (30/tube) that will be 0.12 x 100 = 12 volts drop.

The chokes will vary considerably with their DC resistance and a higher current choke that has low DCR will likely give tighter bass.

Another thing to be aware of is that the size of the power supply caps is important, I'm presuming these are the Solens.
The standard caps are 32uF and once you start making this larger the sound will become less 'active' or 'lively'.

Often increasing the size of the caps too much can make the sound worse - depending on what you want. Making them
larger generally makes the amp tighter and cleaner. For guitar amps, if it's a modern clone of a vintage amp, I sometimes
put smaller PS caps in as per original spec and the amp can really come to life. But thats not a hi fi amp so you want lots of
character.

Z

Offline klackto

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Re: Leak Stereo 20 Modifications
« Reply #23 on: September 10, 2014, 12:37:59 PM »
Hammond make an open frame choke model 157Q  which is 3.5H,  DCR 98 ohm, 150ma. 400v. 
It's compact enough that it should be just possible to squeeze beneath the chasis.
As much as I like the idea of using a vintage choke (have some squirrelled away in the garage somewhere) , I'd like to keep the Leak looking as stock as possible.
An off board choke with flying leads is out as well as we have an inquisitive cat who has an overwhelming need to investigate anything new in the house. ( As a kitten he'd chew everything, fortunately the Audi Tekne cables I use have a braided metallic sheath that he couldn't quite get through. The vacuum seal on the turntable didn't fare so well  .... but that's a different story!  :o)
Reckon the Hammond choke is worth pursuing?

Offline klackto

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Re: Leak Stereo 20 Modifications
« Reply #24 on: September 14, 2014, 10:04:05 AM »
Well, I went ahead & ordered one. Had to order a few other odds & ends and it was pretty cheap (about $27 US) so no great loss if it doesn't sound any good.
I imagine it should offer an improvement over the resistor if not in the same league as a nice vintage choke.
Meanwhile the 33uf Solen power supply caps I put in have settled in nicely .. a worthwhile improvement over the electrolytics I had in there previously.

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #25 on: September 16, 2014, 01:20:56 PM »
I have been trying different chokes in the 100R resistor spot, and a UTC PA40 does sound very good. I will change back to the resistor in the next week just to check.

Offline klackto

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Re: Leak Stereo 20 Modifications
« Reply #26 on: October 05, 2014, 06:18:14 PM »
Managed to fit the Hammond choke. Very easy as the mounting holes line upto those of the power transformer. Will let it burn in for a while and report. I'm sure not in the league of a vintage UTC or Chicago but an option for those who want something self contained.

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #27 on: November 09, 2014, 05:09:27 PM »
I have been fiddling with the valve compliment of the Leak Stereo 20. I came across two E80CC pinched waste tubes in my valve room, and checked them out on the net, turns out they can be used as a substitute for 12AU7s, as you know the leak in that first position uses a 12ax7, I had replaced that with a 12au7, so in that position only and leaving the other two mullard long plate 12ax7s, i dropped in one E80CC..... and WoW  just brilliant. The question is will it cause the amp any problems, i will need to be check this over time, especially the mains transformers temperature, but for now the sound is just marvellous. Much better than any tube I have tried in that position. The model I am using is a pinched waste E80CC Special Quality made in Holland in 1957 with the Heleen made delta mark on the bottom of this tube not on the side as with later models, the Best available... they are very tall about twice the height of the normal 12au7 or 12ax7. This model pinched waste E80CC is the best out there, and not cheap, but well worth it. Why is the waste pinched on this tube, because up until around 1958 they could not make the glass sides straight. As to why they sound better, most audiophiles say, the thicker curved glass is the reason.
« Last Edit: January 12, 2015, 07:04:27 PM by stevenvalve »

Offline zenelectro

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Re: Leak Stereo 20 Modifications
« Reply #28 on: November 10, 2014, 05:16:28 AM »
Generally speaking if you want to sub a 12au7 for 12ax 7 you should make some circuit changes, they are really different tubes, the au will usually end up running outside it's happy conditions and you won't hear the best it has to offer. The e80cc is a bit different again but ours much more like an au than an ax. If an au sounds good, it's always with trying a bh7, these can sound really good subbing au7's.
If start by making sure the au7 and e80cc are actually even close to working in their proper region.

Surely by now you know how to do this Steven? !!!!  :) :)

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #29 on: November 10, 2014, 02:37:15 PM »
I have read plenty about this tube, talking to Paul (fallsaudio) he has had a good look and feels this tube is fine to use,  Zen, put your cane away, little tommy tucker will try to be good.
« Last Edit: November 10, 2014, 02:39:09 PM by stevenvalve »

Offline zenelectro

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Re: Leak Stereo 20 Modifications
« Reply #30 on: November 10, 2014, 08:05:26 PM »
I have read plenty about this tube, talking to Paul (fallsaudio) he has had a good look and feels this tube is fine to use,  Zen, put your cane away, little tommy tucker will try to be good.

Ok cane away I will be nice to you :)

The AX7 and AU7 are -very- different tubes. Most designs will run an AU7 at 5 to 10 x the current of an AX7. That's a lot.
So if you do a direct sub, the AU7 can easily be almost off the scale with it's operating point. There's a high likely hood that
it won't sound nearly as good as it could. 

The E80 is pretty similar to AU7 so if the circuit is happy with AU7 should be OK with it.


T

Offline Peter A

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Re: Leak Stereo 20 Modifications
« Reply #31 on: November 11, 2014, 10:23:53 PM »
Steve,

I have been using Philips E80CC tubes instead of 12AU7 tubes in my Primaluna Two Amp and STC 4212E amps for years.  The E80CC tubes sound great with heaps of authority.  It will transform any tube audio equipment it is used in. 

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #32 on: November 11, 2014, 11:14:25 PM »
Steve,

I have been using Philips E80CC tubes instead of 12AU7 tubes in my Primaluna Two Amp and STC 4212E amps for years.  The E80CC tubes sound great with heaps of authority.  It will transform any tube audio equipment it is used in.
Why have I not heard of them before, you have been holding out vital valve info. Found 4 more 1961 SQ e80cc straight glass today, gooooooood

Offline rab

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Re: Leak Stereo 20 Modifications
« Reply #33 on: November 12, 2014, 08:38:59 AM »
interesting. Would these be a good choice to replace a pair of 12au7s in the output stage ... of a certain Sabre DAC that shall not be named...?  :-o

Offline klackto

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Re: Leak Stereo 20 Modifications
« Reply #34 on: November 12, 2014, 09:20:39 AM »
Steven did you make any circuit changes (eg:change cathode resistor) when substituting the 12au7/e80cc for the 12ax7 in the first position?
I've been using Tungsol 5751s for all 3 valves in the driver stage and find them pretty good but I like the idea of lowering the gain a little more. Have some GE branded made in Great Britain (Mullard I presume/hope) 12au7s that I can try.
I do need to get some NOS el84s at some stage as currently only have Russian Mullard reissues.

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #35 on: November 12, 2014, 02:20:17 PM »
Steven did you make any circuit changes (eg:change cathode resistor) when substituting the 12au7/e80cc for the 12ax7 in the first position?
I've been using Tungsol 5751s for all 3 valves in the driver stage and find them pretty good but I like the idea of lowering the gain a little more. Have some GE branded made in Great Britain (Mullard I presume/hope) 12au7s that I can try.
I do need to get some NOS el84s at some stage as currently only have Russian Mullard reissues.
The leak has a massive amount of gain with the 12ax7s, putting in the 12au7 means you are going from about 100 (12ax7)  to 20 (12au7) gain, dropping the gain means a less forced, more relaxed sound, but still having plenty of gain, plus 1950s 12au7 mullard long plates are cheaper than 1950s mullard 12ax7s long plates. Short plate later mullards 1960s are OK. No circuit changes.
« Last Edit: April 07, 2015, 09:10:12 PM by stevenvalve »

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #36 on: November 12, 2014, 02:21:53 PM »
Steven did you make any circuit changes (eg:change cathode resistor) when substituting the 12au7/e80cc for the 12ax7 in the first position?
I've been using Tungsol 5751s for all 3 valves in the driver stage and find them pretty good but I like the idea of lowering the gain a little more. Have some GE branded made in Great Britain (Mullard I presume/hope) 12au7s that I can try.
I do need to get some NOS el84s at some stage as currently only have Russian Mullard reissues.
I have all the tubes you need just ring when ready.

Offline Peter A

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Re: Leak Stereo 20 Modifications
« Reply #37 on: November 12, 2014, 05:56:35 PM »
Steve,

The Philips E80CC tubes were in the STC 4212E amps when you heard them.  They are a fantastic tube with balls.  Pity there is not a E8#CC variant for the 12AX7 tube. 


Offline klackto

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Re: Leak Stereo 20 Modifications
« Reply #38 on: November 12, 2014, 07:16:51 PM »
I have all the tubes you need just ring when ready.
Thanks, will do!
Been meaning to pay you a visit for ages so will be in touch soon.

Offline stevenvalve

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Re: Leak Stereo 20 Modifications
« Reply #39 on: November 14, 2014, 02:16:49 AM »
I have been modifying the standard Leak stereo 20, I wanted it to sound good on the cheap, First i fitted 4 Hovland .47 music caps, early one's, then 4-1W Shinkoh resistors 10K. Tonight i dropped in 2 Jensen electrolytic, one dual 100Uf to replace to cap nearest the transformers and one dual 47UF down the other end. That improved the sound dramatically. It now sounds really good.
« Last Edit: November 14, 2014, 02:52:22 AM by stevenvalve »