Hello to everyone.
I am an happy owner of one of these cool crate VC5212 90's amplifiers.
1) I have applied to it the modification explained in an old post find on the web (the last row speaking about C5 is mine):
R11 - change from 221k to 100k
C1 - remove
R12 - change from 2.74k to 1.5k
R59 - change from 470k to 242k
C11 - change from 470pf to .0068uf
Add 47pf ceramic cap between pins 1 and 2 of V2 (this improves high frequency stability, and a smaller value may work just as well)
C40 - remove
C5 - change from 22nF to 47nF for reduce bass frequency overload due the previous C40 removing!
Now the clean channel is more like e fender channel without fixed bright switch on and the lead channel is more Marshall JTM like then before!
2) I have replaced the TL072 spring reverb driver with a last generation OPA2134 dual opamp and the reverb become more clean and noise free!
3) In addition to I have experimented the possibility to add a bias tremolo circuit to it's power stage:
As you can see from the schematic the B- bias voltage (-15V) is brought to the output stage valves through a passive jump; so I have remove this jump replacing it with a 250K pot, the center lead to R41/R42 node, one lateral lead to the B- voltage and he other lateral lead through a 1uF capacitor I have applied a triangular wave. Surprise! The tremolo work! But I have notice that the output valves grid pulsing blink.
It's normal or this operation damage the life of the output valves?