Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: finkaudio on June 02, 2020, 11:14:35 am
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Hi,
I'm working on my Guyatone GA-1050 again. It's basically a Fender Twin SF with only two output tubes.
So far, so good. Added a tube rectifier for fun, changed the transformer and got some really nice results with it. Added some shielded cable to reduce the Reverb hum at high settings and added a switch to the Intensity Pot of the Tremolo to disable it. Adds some extra gain, but now I could hear the tremolo ticking. Nothing wild, but after I turned up the speed control to the highest value, it started to go wild....means the ticking now was a plopping and really loud. Did the usual thing and changed the lead dressing, added shielded cables, added the Fender recommendation of a 10n capacitor from the 10M resistor to ground and all made the ticking lower, but not at the really end of the speed setting.
Plopp, Plopp.:BangHead:
OK, the next step was checking voltages and when I touched the Anode of the oscillator, the plopp stopped and everything was dead quiet. And yes, all voltages OK. Only a piece of wire touching the Anode was enough, so no chance to see what was going on even with a 1pF probe of my Scope. I added a few k as grid stopper and that killed the obviously wild oscillation. I'm pretty sure, a few pf from the Anode to wherever would have stooped as well.
Have you ever noticed such behaviour before? I used ceramic NP0 capacitors in the oscillator, as they are really small, low tolerance and I had them sitting here. Normally, I use Orange Drops, but I thought, it's wasted material for the Tremolo :icon_biggrin:
So. anyone had this before? Did not find anything on the net. Good thing now is after all the changes, the amp is dead quiet :-)
Best regards
Karl-Heinz
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I haven't heard of that. I would replace the filter cap that supplies the tremolo.
A quick fix is to turn the trem off with the footswitch anytime your are using that boost switch.
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I haven't heard of that. I would replace the filter cap that supplies the tremolo.
A quick fix is to turn the trem off with the footswitch anytime your are using that boost switch.
All capacitors are fresh.....I'm waiting for a potentiometer with a double switch. However, now it's quiet.
ATB KH