I am busy with restoring a Stereo 20 and came across an old thread here from 2004....
http://www.diyaudio.com/forums/tubes-valves/46856-leak-stereo20-rebuild.html
In this thread esteemed member EC8010 put forward the following advice regarding the Leak output transformer:
"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."
I would really like to do this mod to my transformers while I have them apart. I will be driving mainly 8 ohm speakers but will probably be using the 4 ohm taps. If somebody could guide me which points to join up as per the pic of my actual transformer I would be very grateful! Also the diagram below from the old thread which I dont quite understand
thanks for bearing with me! 😀
Leak OPT Diag by Bregtje Cals, on Flickr
My transformer with the shells off looks like this:
Leak OPT by Bregtje Cals, on Flickr
http://www.diyaudio.com/forums/tubes-valves/46856-leak-stereo20-rebuild.html
In this thread esteemed member EC8010 put forward the following advice regarding the Leak output transformer:
"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."
I would really like to do this mod to my transformers while I have them apart. I will be driving mainly 8 ohm speakers but will probably be using the 4 ohm taps. If somebody could guide me which points to join up as per the pic of my actual transformer I would be very grateful! Also the diagram below from the old thread which I dont quite understand
thanks for bearing with me! 😀Leak OPT Diag by Bregtje Cals, on FlickrMy transformer with the shells off looks like this:
Leak OPT by Bregtje Cals, on Flickr
It is true that it's better to use all windings, but I can't say how big the difference is.
The statement that on the 4ohm tap you are only using half is not complete: it is half compared to the 16ohm tap.
You can parallel the 0-4 with the 4-16 windings, which results in a single 4ohm secondary. There will be no 8 and 16ohm taps anymore.
The statement that on the 4ohm tap you are only using half is not complete: it is half compared to the 16ohm tap.
You can parallel the 0-4 with the 4-16 windings, which results in a single 4ohm secondary. There will be no 8 and 16ohm taps anymore.
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If it was my amp, I would not modify the OPT connections and leave it factory stock.
I had a Leak Stereo 20 (metal brown) a TL25+ (dark metal grey) and still keep a Stereo 60 (dark metal grey) that I restored, and these amps at least meets or exceed their original specs.
So I wouldn't go further in the "improvement" field on a vintage Leak, but it is only my humble opinion 😉.
A+!
I had a Leak Stereo 20 (metal brown) a TL25+ (dark metal grey) and still keep a Stereo 60 (dark metal grey) that I restored, and these amps at least meets or exceed their original specs.
An externally hosted image should be here but it was not working when we last tested it.
So I wouldn't go further in the "improvement" field on a vintage Leak, but it is only my humble opinion 😉.
A+!
Hi Tubelectron I have 2 grey stereo 60s I could use getting to same great condition as yours there - how did you do it?!
Also the diagram below from the old thread which I dont
quite understand
Hi,
The diagram shows two equal secondaries which give 4 and 16 ohm
taps. The top secondary has an additional tap at ~ 40% for 8 ohm.
(The tap is drawn poorly, implying its only about 20%.)
Say the amp is producing 1V per secondary.
Then 1V/1.4V/2V taps will be available for 4/8/16 ohm matching.
You could argue the 16 ohm tap is essentially useless with
modern speakers, and the 4 ohm tap wastes half the winding.
The real question is how optimum is the 8 ohm tap ?
It uses near 70% of the secondary winding.
Your choices are 4 ohm 50%, 8 ohm 70%, 16 ohm 100%, or
rewiring the the two secondaries in parallel for 4 ohm 100%.
(The 40% tap in parallel cannot serve any useful purpose.)
TBH depending on the speakers used I've got sympathy
for both leaving it the way it is or going 100% 4 ohm.
For sure the best "quality" option disregarding output
power matching would be the parallel 4ohm wiring.
(As implied in the thread linked to in post #1.)
rgds, sreten.
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Since the feedback is pulled from the 16 ohm tap I would think you would have to change the feedback resistor network to compensate.
Well...
When I was given this LEAK Stereo 60 amp and matching Varislope Stereo preamp, both were "protected" by a thick coat of... Dust and dirtyness !
Fortunately the amp cosmetics underneath were undamaged and I could remove the crass satisfactorily with hot soaped water and some alcohol, as far as I remember.
After that, I restored the electronics, replacing all R and C parts that were for most of all faulty or out of specs.
I added a power switch in an existing hole at the center of the back and managed to find the correct connector to make a suitable power cord.
I replaced and finally invalidated the input slide switch, leaving only the low sensivity position active, more convenient for a nowadays preamp or pot-box.
Unfortunately, the preamp suffered more on its faceplate, where the graphics, colors were too damaged after cleaning. It is still in its original condition, awaiting in a carton.
Here are some pictures of my restored Stereo 60 and (now sold) TL25+ :
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
But again, the transformers are still factory-wired, unmodified on both amps.
A+!
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Thanks gents, seems maybe there is not that much to be gained by making this mod to the transformers. I think my goal is to get the Stereo 20 up and running in almost stock configuration with updated passive components and a good set of tubes and see where it goes from there. Tubelectron your 60 and 25 look fantastic!
My next challenge is getting the mains transformer repainted from grey to gold.
My next challenge is getting the mains transformer repainted from grey to gold.
Dust as a protector - never heard that happen before! It seems they've been kept in very stable environment, my two have probably been put in garage at least once in their lives... Paint and laquer both flaked in places. I have already modernised the underside and topside capacitors and resistors, but ultimately they'll have to be dismantled for paint and silkscreen rework...
The preamp texts are notorious problem - they merely knock off as finger passes ver fragile. I have many such faceplates I'm considering doing up getting refinished and screened once again.
The preamp texts are notorious problem - they merely knock off as finger passes ver fragile. I have many such faceplates I'm considering doing up getting refinished and screened once again.
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For my main reservoir capacitors I used these - they're a bit taller than normal stock JJ 500V versions....
500 Volt Dual-Section Electrolytic Capacitors (Clamp Mount Type with Solder Lugs)
500 Volt Dual-Section Electrolytic Capacitors (Clamp Mount Type with Solder Lugs)
Thanks !
Yes, I agree : it is exactly what I have done on my Leaks. You should not be disappointed, so you may not need to go further, IMHO.
Yes. I was the first to be surprised myself, because I thought that the finish was dead under the crass. I have been lucky...
This amp was given to me with its preamp as dead. It has been used for years in a bar-restaurant, and what I call crass was in fact a combination of dust, grease and cigarette smoke deposit that against all odds proved some kind of... Protective !
Unfortunately, this treatment was not convenient for the preamp faceplate, which is not really presentable :
An externally hosted image should be here but it was not working when we last tested it.
Some other pictures showing the preserved condition of my Leak Stereo 60 :
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
And what I suspect to be the mfg. date of the amp :
An externally hosted image should be here but it was not working when we last tested it.
Which seems to be in accordance with the date found in the matching Stereo Varislope preamp :
An externally hosted image should be here but it was not working when we last tested it.
A+!
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