"Thumping" tremolo circuit

[EETStudent]

Is there a common cure for this? I do not have a schematic unfortunately. I do not see a optoisolator however. It appears to be adjusting power tube bias, as they flicker with the tremolo. What kind of trem is this?

The thumping only happens at and just around max settings? Backing off either the speed or depth does away with it, however I dont recall the thumping being present when I first bought the amp. Is there a particular something I should check, or is the question too broad?

[Dave Curtis, dB AudioTech]

Make? Model?

It's a bias-shift tremolo.

[EETStudent]

http://www.schematicheaven.com/fenderamps/vibroverb_6g16_schem.pdf

The tremolo circuit is the same in mine as is in this vibroverb, except a couple differences. I have another post under theory and design about the few differences in my amps tremolo circuit and this one, hopefully maybe Ill figure something out

[Dave Curtis, dB AudioTech]

All trem circuits will make 'pumping' noises to some degree. Maybe you didn't notice it when you first got the amp?

Older or mismatched output tubes will have an effect on this.
How many hours do the OP tubes have on them?

Is this a homebrew amp?

[Rob Mercure]

Why would mismatched output tubes affect tremelo thumping?

[Gtr_tech]

Bias needs to be set correctly for that style trem to operate right. Common scene for me to have princetons and the like come in after the owner has replaced the tubes then they notice the trem is weak.

[Dave Curtis, dB AudioTech]

Why would mismatched output tubes affect tremelo thumping?

Generally:

They hum more than matched tubes and that hum, when oscillated by the trem ckt, can make the 'thump' more pronounced.