Gretsch 6159 Tremolo thumping

[aabbs20]

Hey all,

I've got a Gretsch 6159 on the bench, the tube rectifier version. The amp sounds great and doesn't need much work but when the volume is turned up in either channel, you can hear the tremolo is thumping, even when the trem is all the way down or shut off with the footswitch. It seems like it may be a design flaw, as the trem tube shares a filter cap node with the rest of the preamp.  I can see the plate voltage on the other preamp tubes moving around by 5 volts or so.

Have you guys encountered this before? Is there a fix besides adding another filter cap node?

Thanks!

[shooter]

no experience with that amp, does appear a bad design with to many tubes on a tap and low Cap values

[HotBluePlates]

I've got a Gretsch 6159 on the bench ... the tremolo is thumping ... Is there a fix besides adding another filter cap node?

The fix is a different design.  This type of tremolo (pumping a preamp gain stage cathode) will almost always thump.

Leo Fender's first claim to fame was the patented circuit in his 1955 Tremolux, where the trem signal is applied at a push-pull stage to kill the thump.

Yes, maybe Gretsch/Valco cheaped out on the power supply, but very likely you can only ever minimize, rather than solve, the core issue (probably by reducing the amount of trem-depth)

[DummyLoad]

Disconnect the cathode coupled LFO driver?  A switch inserted between "A" points in the posted schematic. 


--Pete