Tube Amp Archive

no, not that cap, its the silver one with 0909 or 6060 written on it

ok so i think i found the problem, i have set my bias to -110v which is max i can get, hooked up my DMM to pin 5 and started poking around, i saw a suspected cap near the bias trim (C37) that looked kinda damaged, as i poked it the reading started going to -1.5v. so that cap definitely is part of th...

usually when i flip the amp on its back or the other way around the problem either comes or goes.

so now i've tried to recreate the problem by knocking around the amp and moving connectors with a chopstick, its working fine now, but there definitely seems to be a problem somewhere maybe a loose connector from the bias supply perhaps ??.

returning it is not an option right now, as there are no blackstar authorised dealers where i live and the shop that it was bought from offered to exchange it with a 50w version (musicians warehouse Dubai)

with the tubes pulled out and amp fully running i get:
pins 3 = 496v, pins 4 = 490v, pin 5 = -1.5v on all tubes

so we got a bias problem here that somehow jumps in and out. any ideas what to check ?

EDIT: i knocked on the amp and the reading on pin 3 changed to -54v

[IMG:640:360]http://imageshack.us/a/img593/9139/3fkq.jpg[/img] the blue glow that accompanied the red plating. [IMG:640:360]http://imageshack.us/a/img850/3585/8eos.jpg[/img] here's my data (all taken on standby): - wrong value fuses installed (3.5A instead of 2A MAINS and 1A H.T) will replace them w...

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If you had a plate to filament short you most likely have blown fuses. I would be checking the bias supply first.

TM[/quote]

maybe the fuses installed are wrong values ?

i poked around the circuit with a chopstick hoping to find something loose, but everything seems good.

i'm not talking about the normal blue glow, this glow is only in the core of the tube and can be seen between the plates, and it only happens when the tubes red plate. when the amp runs fine that glow doesn't occur. all of this is on standby. i have worked on and restored an old fender before. i kno...

hi there, i have a blackstar S1-100, it belongs to my friend who bought it used, this amp intermittently red plates once the power switch is flicked (on standby), it has EL34s, there's a distinct blue glow between the plates whenever it starts to red plate like crazy, within 6 seconds the tubes will...