Crate vintage club VC5212 mods

Tube or solid-state, this section goes to eleven!
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Siro78
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Posts: 19
Joined: 02 Sep 2009, 07:28
my favorite amplifier: Crate VC5212
Location: Parma Italy

Post by Siro78 »

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

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Siro78
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Posts: 19
Joined: 02 Sep 2009, 07:28
my favorite amplifier: Crate VC5212
Location: Parma Italy

Post by Siro78 »

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
Attachments
VC5212 preamp SXX modification
VC5212 preamp SXX modification
VC5212 poweramp SXX modification
VC5212 poweramp SXX modification

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Huevo
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Posts: 4
Joined: 05 May 2020, 13:33

Post by Huevo »

[quote="Siro78"]Hello to everyone.
After some months I have good news about crate ......


Hi Siro78. Long time you put this post.
Well, I have VC5212, which I have converted to 30w, and then removing a pair of power tubes to 15w. I have made also an attenuator to keep the volumen to bedroom level.
I did the first mod that you explain in 2015. Sounds good.. but at least for my ears in the dirty channel too creamy. I mean, I have to lower the Bass al the way down, and the treble al the way up to reduce the very low frecuency response.
Didnt it happen to you?

Perhaps I would preffer something in the midle from original and this mod.

Anyway, I am gointo to carry out the mod that you show in 2017. I would like to get the classic marshall tone, but not too dark :P

Regards

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Siro78
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Posts: 19
Joined: 02 Sep 2009, 07:28
my favorite amplifier: Crate VC5212
Location: Parma Italy

Post by Siro78 »

Hello.
I see this post only now.

I not remeber if 2015 modification had more low frequency on dirty channel, but I still use my amp with 2017 modification and this problem is not present for sure.
I suggest to try the last one modification that is better in absolute.

Rather than, I have this problem on clean channel so I use it with LOW control at 9 o'clock and HIGH control to 5 o'clock.
I don't know why! The tone stack is setted as a traditional fender type.

I plan to reduce the value of C48 for cut of a little the low frequency.

Bye

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