Leak Stereo20 rebuild ? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th November 2004, 09:18 PM   #1
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Default Leak Stereo20 rebuild ?

Hi,

I have a Leak Stereo20 in working condintions (although with replaced resistors and power-supply caps).
Should I leave it as is or are there any good suggestions for a rebuild (without chassis modifications !!).

Thanks in advance,
Jim
  Reply With Quote
Old 30th November 2004, 10:59 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
It's a nice amp. IIRC, it had a bizarrely high sensitivity, so you might look at knocking down the open loop gain by 10-15 dB, then increasing the feedback ratio to maintain constant feedback.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 30th November 2004, 11:12 PM   #3
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Andy Evans who's a member, once started a thread on his mods for the leak 20.

While I haven't had the courage to search for it locally, I did find a webpage describing the work.

I also have a circuit diagram with Glen Croft's mods of that circuit. In case you're interested I could post it here for you.

ANDY AND CHRIS TACKLE THEIR LEAK.........

Cheers,
__________________
Frank
  Reply With Quote
Old 1st December 2004, 12:01 AM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Jim, I probably should have asked first: are you looking for an established design, doing principally parts replacement-type mods, or doing an ab initio design for a totally rebuilt amp?
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 1st December 2004, 12:47 PM   #5
Stixx is offline Stixx  Germany
I am
diyAudio Member
 
Stixx's Avatar
 
Join Date: Sep 2003
Location: Southern Germany
Hi,

I happen to own a Leak Stereo 20 that was heavily tweaked by Steinmusic "http://www.steinmusic.de/" here in Germany.
I don't know what were the exact changes but knowing Holger Stein for some time he sure replaced everything not sounding to his liking. That includes using liberal amounts of his favourite ERO caps (mostly again bypassed) and also MKT in some places. Tweaking Leak's has been part of his business for the last 20 years. Maybe you'd like to give him a buzz......

rgrds,
Oliver
  Reply With Quote
Old 1st December 2004, 02:58 PM   #6
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
One of the best things you can do with a Leak is to improve the output transformer. Most loudspeakers these days are nearer to 4 Ohm than 8 - especially those using a pair of bass drivers. But if you set a Leak to match to a 4 Ohm load, you only use half of the secondary.

If you have the courage to take the shells off the output transformer, you will find that the individual windings are terminated on cardboard strips glued to the coil. You can then reconnect them as shown in the right hand diagram so that you use both windings - which makes for a transformer with reduced leakage inductance - a better transformer, and it cost only a little time. You will probably go one step further and connect new wires directly to the transformer and throw away the phenolic tagboard at the base of the transformer and its associated old wires.

Having tweaked the secondary, you'll probably look at the primary and see that it's possible to replace the wires there too. The PVC-covered wires solder to little solder tags inside the paper windings, and it's perfectly possible to desolder them and replace them with longer wires that go directly to the valve sockets.

Although it's highly desirable, reducing the gain of a Stereo 20 can't be done easily. You'd probably do better rebuilding it completely with a different driver. A differential pair with CCS might be nice. There was a thread about this recently.
Attached Images
File Type: gif leak.gif (6.2 KB, 265 views)
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 1st December 2004, 03:57 PM   #7
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Quote:
Originally posted by fdegrove
Hi,

I also have a circuit diagram with Glen Croft's mods of that circuit. In case you're interested I could post it here for you.

Frank, that would be nice !


Quote:
Originally posted by SY
Jim, I probably should have asked first: are you looking for an established design, doing principally parts replacement-type mods, or doing an ab initio design for a totally rebuilt amp?
I would like to do a total rebuild (but still using 9-pin tubes) with a lower input sensitivity.
But I do not want to overstress the powertransformer so I guess this rules out types like the 5687.


Thanks,
Jim
  Reply With Quote
Old 1st December 2004, 06:10 PM   #8
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
OK, in that case, I'd agree with EC8010; a nice CC diff amp would be perfect. With EL84s, you don't need huge amounts of swing, making the circuit easier- maybe cascoded ECC88s. Morgan Jones recommended a two tube circuit using a concertina, and while that would certainly work well, a cascode CC diff amp has a certain symmetry and elegance that I find irresistable. If you want to go low feedback, a simple CCDA will work well.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 1st December 2004, 06:39 PM   #9
jim is offline jim  Belgium
diyAudio Member
 
Join Date: Jan 2002
Location: Leopoldsburg - Belgium
Default Negative power supply ???

Problem with differential pair with CCS is that you need a negative supply.
I don't feel like putting another powertransformer under the chassis.
Any suggestions ?

Jim
  Reply With Quote
Old 1st December 2004, 08:00 PM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Once you get rid of that big tagboard, a lot of room becomes available above and below the chassis; room for an HT choke and a big HT capacitor for the output stage. By comparison, a transformer to provide a -15V supply (which could also be used for grid bias of the output valves) is trivial. Give it some thought. Without the negative supply, your options are more limited.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anyone heard a Leak 70 ss amp ? ashok Analog Line Level 6 8th July 2009 11:14 PM
Leak Tl/12+ Psychobiker Tubes / Valves 4 6th March 2008 10:06 PM
Leak Stereo 20 rebuild/restore question alanr Tubes / Valves 6 9th January 2005 11:22 AM
Leak tl/25+ OPT selection avxt Tubes / Valves 12 21st September 2004 02:22 AM
Motorboating in leak 20 bronto64 Tubes / Valves 5 13th August 2004 11:49 AM


New To Site? Need Help?

All times are GMT. The time now is 12:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2