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Valves are here (very quick service) shall deal with them after the gardening... The priorities of a family man.

Sorry to piggy back on dezb1's thread but i've noticed my GVT15H becoming dull sounding on the lower wattage mode. Looking at the manual (http://www.ampeg.com/products/gvt/manuals/GVT15H_OM.pdf) it says that this could be due to power tubes needing replacing. It gives instructions on how to replace the power tubes, but there is no mention of re-biasing the amp. I thought that amps always needed re-biasing when power amp tubes are replaced, is this correct?

Sorted... But slightly confused, pulled valve 1 no change, pulled valve 2 no change, pulled valve 3 sorted?!?. Happy that it's fixed but don't understand what the problem was...

cheers once again for all the advice, saved me a fortune as I'd have had to take it to get repaired.

Well, glad it's sorted but it doesn't make sense.... Valve 3 should be the phase inverter and the FX return is before that so why it was louder in the FX return....

NickS wrote:Well, glad it's sorted but it doesn't make sense.... Valve 3 should be the phase inverter and the FX return is before that so why it was louder in the FX return....

exactly... Thought I was beginning to understand how it all worked now I'm back to thinking is all black magic... Or incorrect wiring.



third valve from the right... T'is valve 3 no?

That's what it says in the user manual...

NickS wrote:That's what it says in the user manual...

started working when i swapped it for the new one???

johnnyseven wrote:I thought that amps always needed re-biasing when power amp tubes are replaced, is this correct?

Depends on the design of amp. Self-biasing output stages (typically used in lower power amps) don't need or have bias adjustment.

PI valve was haunted

You did the right thing bro