Custom 6sn7 preamp runs too hot

Posted by Cuernavaca (A) on May 12, 2017 at 10:36:09

A few years back I bought a custom preamp from a midwest builder who seemed to know his stuff. It uses 3 6sn7 tubes and sounds exceptional. I also have a Mapletree preamp to compare it with, and the custom preamp has better/deeper soundstage, more defined bass, etc. But the Mapletree runs cool, the other runs so hot you could fry eggs. I've had to replace the 47uf caps in the power supply, they seem to fail and create hum after a short amount of time. A local engineer rebuilt it 3 years ago and he seems to think the caps were faulty and their failing has nothing to do with the design.

My question is, what is making this run so hot? I may try to install a small fan to help dissipate heat. Tube life hasn't been an issue. Power supply sits on top and doesn't seem to be affected by the heat, it stays just lukewarm.

Any ideas would be appreciated. I can post the schematics if that would help, the original builder has since passed away.

Thomas

"I've never owned a firearm, but I do have an attack parrot!"

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Topic - Custom 6sn7 preamp runs too hot - Cuernavaca 10:36:09 05/12/17 (24)

Preamp revisited - Cuernavaca 11:40:40 08/2/17 (0)

Pull it out from enclosed area - Charlie8521 09:17:06 05/13/17 (0)

holes in top plate - RayP 05:23:50 05/13/17 (2)

Thanks everybody for the help. - Cuernavaca 09:04:31 05/13/17 (1)

RE: Thanks everybody for the help. - GEO 18:35:34 05/14/17 (0)

RE: Custom 6sn7 preamp runs too hot - Johno 17:42:10 05/12/17 (0)

RE: Custom 6sn7 preamp runs too hot - Paul Joppa 16:53:52 05/12/17 (0)

Shunt zeners - Salectric 15:34:37 05/12/17 (0)

RE: Custom 6sn7 preamp runs too hot - DAK 14:31:24 05/12/17 (0)

Also, wood is a rather good insulator compared to aluminum or steel~nT - Cleantimestream 13:32:56 05/12/17 (0)

RE: Custom 6sn7 preamp runs too hot - DAK 12:57:34 05/12/17 (3)

And that brings up the point... - Triode_Kingdom 14:17:44 05/12/17 (0)

RE: Custom 6sn7 preamp runs too hot - Cuernavaca 13:46:35 05/12/17 (1)

RE: You still might want to post those numbers... - DAK 14:17:22 05/12/17 (0)

RE: Custom 6sn7 preamp runs too hot - Tre' 12:13:35 05/12/17 (4)

bottom is ventilated - Cuernavaca 13:44:10 05/12/17 (1)

RE: bottom is ventilated - Triode_Kingdom 14:19:05 05/12/17 (0)

What he said... - Triode_Kingdom 12:44:52 05/12/17 (1)

RE: What he said... - deafbykhorns 05:43:59 05/13/17 (0)

RE: Custom 6sn7 preamp runs too hot - OldNuke 12:10:53 05/12/17 (0)

Schematic? Shelf? - Lew 10:44:06 05/12/17 (3)

RE: Schematic? Shelf? - Cuernavaca 10:58:25 05/12/17 (2)

RE: Schematic? Shelf? - awesterner 01:11:52 05/13/17 (1)

RE: Schematic? Shelf? - awesterner 01:36:08 05/13/17 (0)

Custom 6sn7 preamp runs too hot

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