RE: Custom 6sn7 preamp runs too hot

Posted by Johno (A) on May 12, 2017 at 17:42:10

In Reply to: Custom 6sn7 preamp runs too hot posted by Cuernavaca on May 12, 2017 at 10:36:09:

Pretty amp I love wooden chassis.

Looking at schematic the valves appear to be dissipating around 4.5W per channel, 9W collectively. A 6SN7GTB has a absolute maximum combined plate dissipation of 7.5W so you are well within those ratings collectively across 3 x 6SN7. This assumes the valves are operating as per schematic this can be confirmed with a DVM.

But as Tre & TK suggested the combined heat generated from plate, Kathode & power supply dropping resistors and with no ventilation holes on top plate, heat ramps up quickly.

I would try running the amp with the bottom on & also removed & elevated for comparison. Measure the top & internal temperature with a IR laser gun. This will tell what the inside chassis temp is running at. I suspect those PS caps are failing due to excessive internal temperature (they are located close to top plate)also note that aluminum top looks to be no more than 1-2mm thick, this heats up quickly. Remember there are 2 ways heat can be removed air convection (fan) or radiation (reflection)

A small fan run above the amp top will certainly help.

Johno

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

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

Preamp revisited - Cuernavaca 11:40:40 08/02/17 (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)

Follow Ups

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

RE: Custom 6sn7 preamp runs too hot

Post a Message!