stumped; Fender pre-CBS Concert 6G12a trem issue

[tim]

Hey all,

I have a Fender Brown Concert Amp (circuit 6G12a) on the bench...all is well with the amp except when I turn the trem intensity above 6-7, it starts thumping like crazy, with or without sig applied...and it's not even a "clean" thumping but somewhat distorted (sounding and on the scope). I have replaced all tubes in circuit, replaced trem circuit caps with orange drops, etc etc...voltages are all clean and correct...

Mind you, this is not the trem with a "opto" bug in it that Fender used in other amps.

Any suggestions from the sages here? I'm out of ideas.

Thanks

[tim]

figured it out...bad 2uf cap...changed and all is good. Still a bit of thumping but it's 95% gone.

[seeley]

Hi Tim. If it helps I use heavy duty LCR hi fi caps in trem circuits. They seem to last the distance

[MWJB]

this circuit is prone to thumping, even when working properly, care is advised when adjusting speed & intensity controls.