jcm 800 wierdness

[p3bufny]

Couple of quick questions.

I just replaced my 5 yr old GT E34LS tubes
with a brand new set of GT E34LS tubes. According to Groove Tubes
no bias adjustment is needed when replacing Groove tubes of the
same output. Is this true????

I noticed something strange last night. With Gain and pre volume
near maximum, and master-volume at zero, signal is still coming through.
( I can hear the guitar even though amp volume is at nil.)
This just started a couple uses after my un-biased tube replacement.
Any idea what it could be???

[MWJB]

If the 5yr old tubes were correctly biased in your amp when they were installed, then yes - the new tubes of the same grade, manufacturer & type should be safe enough to go in without causing any damage.

It's probable that this bleed thru at zero volume was always there (I'm assuming that it's relatively subtle, not like gigging volume), there is no reason to suggest that it is happening because of the new power tubes. Some amps do it (pre volume pot may not actually read "0" ohms when fully counter clockwise, or the signal is being picked up elsewhere in the circuit), some don't.

[Amp Kat]

Can't say it's not bias related depending on where that bias voltage is but after 5 years it may be a good idea to at least check your bias and see where it's at. Then you could plug and play with the same tubes and be fine after that. Remember that old 6L6 tubes were 23 watters and most current production GC's are 30 watters. I also agree with Mark that the pot could have a little resistance or the pot know may not be allowing the pot to turn fully counter-clockwise .

[p3bufny]

If the 5yr old tubes were correctly biased in your amp when they were installed, then yes - the new tubes of the same grade, manufacturer & type should be safe enough to go in without causing any damage.

It's probable that this bleed thru at zero volume was always there (I'm assuming that it's relatively subtle, not like gigging volume), there is no reason to suggest that it is happening because of the new power tubes. Some amps do it (pre volume pot may not actually read "0" ohms when fully counter clockwise, or the signal is being picked up elsewhere in the circuit), some don't.

I tested both pre and master volume pots. both read 0 ohms when when fully counter clockwise.
Also discovered that it doesn't matter which volume pot is at full.
One at full (or close to full) and one at zero still gives me signal.
Not concert level but certainly "plinking around" level. I guess it isn't a huge problem, but I used to be able to count on the ability to stop signal with one volume control.