Crate vintage club VC5212 mods

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Crate vintage club VC5212 mods

Postby Siro78 » 19 Jan 2015, 13:27

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):

Lead channel
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)

Clean Channel
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?

Thanks
Siro78
 
Posts: 17
Joined: 02 Sep 2009, 08:28
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Re: Crate vintage club VC5212 mods

Postby Siro78 » 08 Mar 2017, 18:36

Hello to everyone.
After some months I have good news about crate VC5212 vintage club amp modification.

I have tried a lot of mods on my but at the end I find that a classic modification is the best for it!
The real problem of the dry channel is the even number of gain stage that in any way introduce artifacts to the sound and the only way for eliminate these oscillations is put capacitors. This corrupt the sound.
Do not have sense use a low mu tube and obtain a good gain factor using an additionl stage!

So this is what I have done on dry channel:
- removed one gain stage
- biassed the remaining 3 gain stage with classic marshall value
- used EHX 12AX7 high mu valve
For all these modifications I have tried to use component already present on the board or putting in parallel to existing component other ones.

I attach the schematic modification.

In addition I have introduced in an easy way a bias tremolo on the power stage. The EL84 tubes have a bias near the -11V so using the -10/+10V power supply already present on the board and a pair of opamp it's possible to create a good bias modulation!

Now the clean channel sound like a fender, the dry channel have classic marshall tone and in addition it have reverb and tremolo!
It is my definitive amplificator.

Bye
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Siro78
 
Posts: 17
Joined: 02 Sep 2009, 08:28
Location: Parma Italy
Has thanked: 2 times
Have thanks: 14 times


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