Repair I couldn't turn down.

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Nigel Goodwin

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I don't really do repairs any more, but when an old friend's daughter contacted us we couldn't turn it down

As you can see, the selector switch is dangling - as I removed it. It had obviously had a bang on the front of the knob, as the rear of the switch was displaced, I pushed it back in place, but it still doesn't feel right - so I've ordered a new switch.

 
It's nice to see items where the physical device and the circuit diagram probably have the same layout.

I was rather disappointed to see that there's no circuit diagram in the instruction book

Not that you need one for a simple valve amp, but it would be nice if it was there.
 
Classic hand wired chassis. Love how looking at the component layout you can see each channel of the stereo.

Ron
Nice isn't it

I've just noticed in the picture, there's a spring in the bottom left hand corner (near the mains socket), must have fallen out of the broken switch?.
 
The busbar wiring in the middle and the flying diodes over the caps in the lower left corner take me back -

Back in the early 70's when I was in school and building a TV station, part of it was hand-building some 24 Vdc, 10 A linear power supplies on 3U and 4 U rack panels (public TV station, no money to buy commercial units). Control transformer, big black diamond bridge, and large "computer grade" electrolytic caps. The wiring was open frame using #10 bus bar in what we called "refinery wiring" - exactly as in this amp. Lovely.

ak
 
I've pulled plenty of those switches apart and never seen springs like that in them.
Must admit, neither have I? - anyway, I've removed the spurious spring, and fitted the new switch - all inputs now work (on a buzz test), got to bring a phono to 3.5mm jack lead in tomorrow to stick some audio through it.

The faulty switch by the way is made by Alpha, and I can't see any kind of spring to operate a detent mechanism, so perhaps that was the spring?.

Just had a close look - there's a hole right through the switch shaft (inside the body), that spring must go through the hole, and have a ball bearing at each end?.
 
I think I've got one or two faulty ones in the shed I can pull apart and check.
Not the best of pictures, you can't see the detents in the body - but I've slid the spring in the hole in the shaft, and if you push it right in it's about flush with both sides, ideal for a ball bearing either end to sit in the detents.



BTW, it's playing AC/DC at the moment
 
Turns out you're right - there should be two ball bearings somewhere.

And to think I've just been chucking these out, I could have had a nice stock of springs and ball bearings


 
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