fizz and oscillation in Peavey Rockmaster head

[garyhb]

re fizz & oscillation in Peavey Rockmaster 120watt head

Just joined - great forum!

I've owned a Peavey Rockmaster 120 watt head (not the preamp) for 20 years (moded version at: [ame="http://www.youtube.com/watch?v=uH0_iXP0TIw"]YouTube- FJA Modded Rockmaster amp 1[/ame]).

Two probs:
1. Recently it's gotten very fizzy during overdrive
2. Signal oscillation is present especially on lower notes (sounds like gentle vibrato/tremolo)

I'm running it with 2 power valves pulled, through the main out into a single Celestion Sidewinder (150w @ 8 ohms). All valves are recent JJ Teslas.

Enzo (Peavey Rockmaster pre mods - Page 2) has suggested replacing PSU caps which makes sense for the oscillation. I figured these and other elec. caps might need changing.

I have found this http://music-electronics-forum.com/t15597/ thread interesting and wondered if it's relevant?

BTW I studied some electronics years ago and am happy doing some fault finding and repair...

Any help is greatly appreciated.

Gary

[Gtr_tech]

First thing I'd check is solder joints on the tube sockets....for that matter look over all pcb's for cracked solder. Good place to start.....
If it has loop/patch jacks clean those for good measure, or just patch a short cable from the in/out or send/return to see if it makes a difference. If it does, they need cleaning and/or deoxidising.

[garyhb]

RM fizz

Thanks Gtr_tech

I have done this a while back but I'll go over it again. I was wondering if fizz could be caused by preamp filters breaking down?

Happy new year!

regards

Gary

[Chuck H]

I was wondering if fizz could be caused by preamp filters breaking down?

Sure. But it's not the first thihg I'd check. I'd check the tubes first.

And... As per Enzo's suggestion, if you've had the amp for over twenty years the it could probably use a cap job AND tubes.

Chuck

[garyhb]

Fizz in Rockmaster 120 watt head

Hi Guys

Well, this morning I resoldered all the valve bases, some dry joints and some dodgy looking fx loop wiring, used switch cleaner on the valve sockets and jack inputs. All working fine now. Fizz seems to have cleared. The sound was always bright but I suspect that's also something to do with the Sidewinder speaker.

There's still a slight oscillation, but I suspect that might be the guitar setup...Anyhow, I'll replace the caps, not the valves as they're pretty new.

I suppose the amp ought to be mothballed for a newer one, but for now it sounds just fine again .

Thank you for your wisdom and a happy new year.

Gary