repair of a Counterpoint SA-5 preamp

gjaky
Master Tech

Posts: 642

repair of a Counterpoint SA-5 preamp Aug 9, 2017 3:14:40 GMT -5

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Post by gjaky on Aug 9, 2017 3:14:40 GMT -5

I got a counterpoint SA-5 all tube preamp for repair. It proudly says it was made in Beverly Hills, California U.S.A. It sounds awesome isn't it?
I was told that there is no light, no sound from the amplifier.
After opening up I saw this:

Those caps blew up a little...

I started to study the schematics and realized that the caps are quite underrated, they put 250V rated capacitors where the rated voltage is 250V (or even more), in fact they put 200V film capacitors across all these 250V lines too, I am surpised it lasted this long.

WTF?

nashou Unmoderated Off Topic Tech in Training..... Posts: 1,239	repair of a Counterpoint SA-5 preamp Sept 17, 2017 19:34:40 GMT -5 Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by nashou on Sept 17, 2017 19:34:40 GMT -5 WTF? Is right!!!! So did you fix this yet? Nashou

gjaky
Master Tech

Posts: 642

repair of a Counterpoint SA-5 preamp Sept 18, 2017 2:21:32 GMT -5 via mobile

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Post by gjaky on Sept 18, 2017 2:21:32 GMT -5

Hi Nashou,

Yes, the amplifier has been repaired already. It turned out that the core of the problem was the weak/worn out main rectifier tube EZ81 (housed in a separate box), because it arced internally under load, and with that AC voltage was present on those polarized capacitors. And because there was no fuse in the supply line it lead to the death of all main filter capacitors. The first capacitors after the rectifier was rated at 500V, for those I had to be creative because there are no such capacitors available now, so I put two 350V caps in series with balancing resistors.‎
I used long life 350V Rubycon YXM capacitors throughout.

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Post by gjaky on Aug 9, 2017 3:14:40 GMT -5

Post by nashou on Sept 17, 2017 19:34:40 GMT -5

Post by gjaky on Sept 18, 2017 2:21:32 GMT -5

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