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Leak Stereo 20 Restoration

Posted <2019-09-10 Tue 22:02> by Aaron S. Jackson.

About 10 years ago, my Dad was given a Leak Stereo 20 amplifier from my uncle, who I think was given it from someone else after it was removed from some weird wooden stereo console. The amplifier is dated 1963, but probably hasn't been used for around 25 years at this point.

Last year, almost exactly a year ago actually, I ordered a new set of tubes for the amplifier, but never got round to repairing it. Here are a few photos of the status of it when I got it.

As you can see, it's clearly had some work done to it before. The GZ34 rectifier socket has been disconnected, and in it's place is a solid state rectifier. There are a bunch of capacitors which have likely been replaced too, but not all of them. The work is a bit scruffy in general. capacitor is sort of hanging out because it was the wrong size.

This weekend I decided to figure out what I needed to buy to get the amplifier in working order. As I said earlier, I had already bought a full set of tubes for the amplifier. I decided to order the following from Farnell.

Caps Value Replacement Part No Qty
C10/C11 & C12/C13 32uF / 32uF, 400V PANASONIC - Electrolytic Capacitor, 47 µF, 400 V EEUEE2G470S 5
C1L/R 1nF, 400V Not replaced yet
C2L/R 50uF, 12V, electrolytic VISHAY - Electrolytic Capacitor, 47 µF, 25 V, MAL203036479E3 10
C3L/R 0.1uF, 350V VISHAY - DC Film Capacitor, 0.1 µF, 400 V, PET MKT1813410405G 5
C4L/R & C6L/R 0.25uF, 350V VISHAY - DC Film Capacitor, 0.22 µF, 400 V, PET MKT1813422405G 5
C5L/R 0.02uF, 350V Same as C3
C7L/R & C8L/R 50uF, 25V Same as C2
C9L/R 200pF KEMET - Multilayer Ceramic Capacitor, 220 pF, 100 V C410C221J1G5TA7200 10

I did not end up replacing C1L/R because I couldn't find an appropriate capacitor. I'm not convinced these capacitors are required and may end up removing them. They are in parallel with a resistor on the output. The GZ34 rectifier socket was rewired after I removed the solid state rectifier.

After installing all of the new capacitors as shown in the schematic, I powered it up. Much to my surprise, the tubes went into emission and I started to hear Beirut. But shortly after I started to notice a bad smell… R20 started smoking, so I quickly disconnected it. After messing around for about an hour, checking all the resistors were ok, it occured to me that C10 and C11 must be backwards. I thought this was weird when I was wiring them up originally, but decided to follow the schematic anyway. After correcting that the amplifier worked great… for a few minutes.

The left channel cut out, so I turned the amplifier off. Everything underneath looked fine so I inspected the tubes. V2L had a small crack in it. Hopefully just a manufacturing fault as the heater voltage is fine. I'll go into town and pick up a few more 12AX7 tubes. Here's a photo of the cracked tube:

All of the tubes were ordered from jjtubes.eu. In total I ordered:

Tube Quantity
EL84 4 Matched
ECC83S / 12AX7 3
GZ34 1

There are still a few things I want/need to do:

I'll post some more photos of the amplifier in it's restored condition once I'm happy with it. For now, here's just one, showing the tubes glowing.

Here's the circuit diagram just in case it goes missing from the web - notice the unusual orientation of C10 and C11, top left.

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Tags: electronics

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Copyright 2007-2019 Aaron S. Jackson (compiled: Wed 11 Sep 17:16:25 BST 2019)