Gibson GA40 Les Paul - Weak Tremolo

[kagliostro]

Few days ago I was saying that I really find of great interest to study old Gibson schematics, yesterday I was on Marzaglia (MO - Italy)

where there was the biggest radio amateur flea market of Italy, there I've find a friend that lives very far from me, he, sometime ago, build

a GA40 Les Paul (and gived me documentation about) so, what better to speak with him of the GA40 ....

He remark me about the tremolo that is weak at his taste, the GA40 has a particular tremolo circuit that I've seen only in the Selmer Stadium

TV19/T, in the Gibson a 6SQ7 triode is used as oscillator whose cathode is connected to G3 of the 5879 tube of the tremolo channel

on the Selmer the tubes are both EF86







Do you think that is possible that the incisiveness of the tremolo is increased modding a bit the existing circuit

or it will be obligatory to achieve the tremolo using a different (and may be more standard) way ?

Thanks

K

[Willabe]

Tone Quest Review mag. did a review of an original GA40 some years ago and they said the trem was very deep, strong and 'throbbing'. They loved that amps trem.

So something must be wrong in your friends amp?


 
                   Brad   

[sluckey]

in the Gibson a 6SQ7 triode is used as oscillator whose cathode is connected to G3 of the 5879 tube of the tremolo channel

It may help with understanding and troubleshooting this particular tremolo modulation scheme if you consider the oscillator cathode is actually connected to the cathode of that pentode preamp tube. The tremolo oscillator signal modulates the cathode bias of the preamp tube causing it to vary the conduction of the preamp tube. The suppressor grid just happens to be strapped to the cathode.

At least that's the way I like to think of that circuit.

[kagliostro]

Tone Quest Review mag. did a review of an original GA40 some years ago and they said the trem was very deep, strong and 'throbbing'

Thanks for the important info Brad

---

It may help with understanding and troubleshooting this particular tremolo modulation scheme if you consider the oscillator cathode is actually connected to the cathode of that pentode preamp tube.

Thanks Steve I was considering more the fact that there is the connection to G3, but surely the important thing is the connection to the cathode

Franco