Weird Sagging happening on Bogner (EL34) Shiva help/advice please

welshboyo

Hi Guys,

Got a bit of a weird thing happening with my Shiva, I initially thought it was one of my Fuzz pedals causing it, but I have tried a few different things front end and its behaving exactly the same way no matter what it is.

Basically, when I'm hitting the front end with a pedal the amp will almost sag but only on neck pickup  -the notes will almost "compress" up and will then almost "bloom" when they start to decay. I know some people like this feel but this is beyond useable - in rehearsals last night when I was switching to neck pickup, the amp was sagging that much it would drop out of the mix!!

If I knock either the guitar volume back a tad or drop the drive on the front end pedal back to almost Zero it tends to clear the issue up.

Chain is  - BudWah - RM voodoo1 - input Gsystem -(Gsystem Loops)Octavio - DejaVibe -SD9 - TS9 (Gsystem Loops) - Front End Amp and then G system back end in the amp fx loop (4 cable)

Taking the g out of loop and just using a drive pedal straight in gets the same thing..

Valves?

ICBM

If it's not valve-rectified I'd check the power valves first. Sounds like it's struggling when there's a lot of bass content in the sound.

welshboyo

Cheers @ICBM, interestingly, I haven't changed out this clicking Valve Heater Power Supply as yet, could that be the culprit?

ICBM

welshboyo said:

Cheers @ICBM, interestingly, I haven't changed out this clicking Valve Heater Power Supply as yet, could that be the culprit?

If the filaments are running quite a lot under-voltage, possibly.

welshboyo

@ICBM thanks for your advice...again...

update - solved this one..and also solved the clicking heater supply..without replacing it (doesn't make sense how/why but it has definitely cured it)

Had my 1st real "dive" into the back of this amp - there was a right mish mash of preamp valves in it ranging from JJ to an old old mullard (which was in V1) replaced that with my trusty old Genalex Gold Lion and instantly the power-up click has gone away....the sag was also much much better but not right, so went on and replaced the rest of the pre-amps (found an LPS in V2??)

The amp is transformed..I will get the Powers change soon and a rebias (got a pair of Winged C's here from karltone ready to go in)

Could a dodgy preamp valve cause both the issues I've had? - sag and this clicking power supply???

ICBM

Yes - particularly if the bad valve was in a cathode-follower position, but possibly even if not. If it was leaking DC to the filament supply circuit, and again particularly if the filament supply is also regulated and so could be sensing that somehow (rather than just rectified and filtered), it could have caused all sorts of mayhem.