New tube problems or something more?


Silver Supporting Member
Late 2012 Dr Z Maz18 NR

Never had trouble with the amp before but it was due for a tube swap so I did just that - still had the factory originals in there. Ordered a stock replacement set from All same brand/model as the factory equipment.

No trouble at first - maybe 5-6 hours on the tubes now. Last week during home practice the amp lost all bottom end and then the volume fizzled out completely. Switched off for a few minutes then powered back up. No problem - back to normal. Last night at rehearsal - same thing. This time I scoped out the tubes before I shut her down. The EL84 in the first socket was BRIGHT red/orange. Definitely not normal and nothing like the tube in socket two - something obviously wrong as the amp had zero volume. Again, shut her down for a few minutes and was fine after a reboot for the remainder of practice.

I'm a player not an electrician - so my knowledge is limited here. Any ideas on what to troubleshoot first? Quick google search suggested leaky capacitors - but wouldn't I have seen that with the previous tube set? Could I have a lemon tube. Anything else?

Big gig coming in two weeks up during halftime of a NBA game, so I want to make sure tubes don't crap out on me! Yikes!!!

Thanks in advance for any help!


Bob Pollock

Altes Holz
Gold Supporting Member
Swap the tubes with each other, see if the
BRIGHT red/orange
follows the tube to the other socket, or if it stays with the first socket. this will tell you if it's a tube problem (if it follows the tube to the other socket) or an amp issue (stays at the first socket). If it's the latter, it's likely a bias supply issue with that socket. Also, try putting your old tubes back in. Hope this helps.


Put your orig el84 back in, see if it goes away. If so they sent you a dud. Call them up and ask for a replacement set.

Ps at a yr and 1/2 old amps original preamps where probably still fine. But at least you got spares now.

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