crate vc 50 3x10

[baddog]

I have a crate cv50 and was thinking about using 12ay7's in in V1 & V2 to lower the gain in both channels a little. What affect would it have on the tone my amp?



baddog

[drlowlow]

I can't find the schematics for this amp and I dodn't know what preamp tubes were already in it but you shouldn't have any problems with the swap so just try it and if you don't like you still have the tubes for a different project.

[baddog]

4 preamp tubes and they are all 12ax7s and 4 el84 power tubes. I tried 12au7 and i lost to much gain and the 5751s didnt drop it enough.

[drlowlow]

I would go ahead and change them out and see how it sounds or another option that wont require much soldering would be to replace the cathode resistors in the preamp with higher valued ones. I have never seen the inside of this amp but a resistor can only be connected on two ends, so it isn't an exptremely involved process). Your amp isn't a rare or vintage collection piece so I say why not give it a go, if it doesn't work out how you like then you can change it back and resistors are alot cheaper than tubes.

[baddog]

Here is the schematic for the amp .

baddog

[drlowlow]

after examining the schematics it looks like there are several options for reducing gain. It sounds like you have tried several different tubes already and I assume you have them on hand so with that in mind lets consider just changing V4 with a lower gain tube. The amp uses EL84s which are pretty easy to overdrive so reducing the gain directly infront of them would help with all channels.

The clean channel is very fenderish. if the initial solution hasn't helped then I would recomend looking at blackface fender schematics for the hi/low gain setup at the imputs of those amps. I think there aren't many people that use the low gain inputs so it is not a surprise Crate decided not to copy this aspect as well. You could add a resistor at the imput that would lower the gain of all channels.

I stated before about changing the cathode resistors to ones of higher value but after seeing the values they seem pretty conservative.

No matter what you do their will be some affect to tone. Tubes just don't operate predictibly which is their charm and why they are still used in music instrument amplifiers after being phased out in most every other market. you have several options availble and you will have to try a few things to find out where in the circuitry is the problem. I would start at V4.

[baddog]

I do have a few 5751, 12at7,12av7and some 12au7s. i was thinking about picking up a 12ay7 and trying that in the amp also. I read that they are used in some fender amps.

Also my guitar amp has a hum that is most noticable in the clean channel. I dont think its a tube or groung problem because i checked them both. The only thing i cant check is the el84's because i dont have the extra cash to purchase new ones to do a swap. I did check them with my b&k 707 tube tester and they all read good. I did some DC voltage checks on the amp without any signal applied and these where the reading i got.

Power Section Preamp

TP Requiered actual TP Requiered actual

12 -4.6 -4 1 147v 192v
13 215 286 2 150 188v
14 209v 311v 3 163v 174v
15 54v 164v 4 235v 246v
16 -275 26v 5 290v 297v
17 -15.6 -15 6 308v 311v
18 381v 367v 7 179v 188v
19 391v 375v 8 180v 189v
20 --------------- 9 -----------------
21 391v 376v 10 0v
22 3.47v 2.96v 11 -10v -9v
23 -3.47 -2.99v
24 -------------------
25 ------------------
26 15.7v 15.11v
27 -15.7 -15.14v
28 10.6v 10.5v
29 -10.4v -10.5v
30 -15.7v -15.8v
I did change out all of the 1/2 & 2 watt resistor with CC type. Some were 10% and some were 5% resistors. I dont think that would introduce hum in the amp but who nows