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Sound Valves M-40 assistance
Sound Valves M-40 assistance
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Old 18th December 2005, 06:28 PM   #1
audioquestM-40 is offline audioquestM-40  Canada
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Default Sound Valves M-40 assistance

I am looking for manual, schematic, and parts list. Anyone know where to get any or all of these?

The dual color indicator light on one of my amps is only partially functional and would like to have it repaired.

Also, what are ok to substitute for EL 34 and 6gh8 tubes?

As you can tell I am completely a rookie at tube gear.

Any and all help wil be greatly appreciated.
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Old 18th December 2005, 08:03 PM   #2
Eli Duttman is offline Eli Duttman  United States
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I can't help with the doc. or the SS parts, but I can help with the tubes.

You should use EL34s as "finals". There are 2 good varieties in production: The SED ("flying C") EL34 out of St. Petersburg, Russia and the JJ E34L out of Jamona, Slovakia.

If you can't source 6GH8s, 6U8s should be OK.
Eli D.
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Old 18th December 2005, 09:10 PM   #3
SHiFTY is offline SHiFTY  New Zealand
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You should only use those types of tubes/valves approved by the manufacturer, i.e. replace EL34s with EL34s and so on.

However the tubes may well be fine.

For good sound, use New Old Stock (NOS) tubes from the 50's and 60's. Mullard/Philips Made in Great Britain EL34s are the best you can get but big $$$.

For 6GH8 you should try all the NOS ones you can get from the different manufacturers, eg RCA, Sylvania etc. eBAY is not a bad place to start looking... be careful of scammers though!
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Old 20th December 2005, 05:46 PM   #4
audioquestM-40 is offline audioquestM-40  Canada
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Thanks. Was looking for the service manual as it has a dual color LED, of whcih one color does not fire. Not sure if it's reverse polarity that activates it or what.

I've currently got Groove Tube EL34's in it, which sound pretty good, and have tried 6u8 in place of the factory 6gh8's. The 6U8 have a bit richer sound, and still provide a lot of detail. I did order a couple other American brand NOS tubes of those varieties to experiment a bit, as like I said, I'm 100% new to tube.

WAF was high so I expect tubes are in my home to stay
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