Crate V5 mods... anyone?

[letter109]

My first post here folks. . .just wnted to say thanks to Tarin for the hi-res schematic of the V5. I tried calling the Loud Technology toll-free number but they're still out on training or something. . .been that way for several weeks now, eh? Anyway, I got the schem from this group and is greatly appreciated. I have three of those little V5s sitting around here, and I actually like 'em OK out of the box. But I also agree with deafelectro that this may be one of the next big things in little amps, and a great beginning place for a heck of a mod. So, if I have success with anything (or even failure) I'll try to let you all know how it came out. Thanks for a great group. I'm glad to be a member of it. -M

[jim p]

The most important voltage on the EL84 would be the cathode voltage to calculate the cathode current. With the 330 ohm resistor this should be approx 14 volts max equal to 42mA. Ballpark you would then have 38mA plate current and 4mA screen grid current. Not sure the 12AY7 may be problem free by the data sheets it is calling for a higher plate current (3mA) and a lower value grid resistor 100k ohms (may have high grid leakage current vs. 12AX7). I also noted on one data sheet a higher heater current so check to see that you have 12.6 volts across the heater. What are the cathode, grid and plate voltages for both locations of this triode? Have you tried the Sovetek tubes that were stock in the amplifier?

[jim p]

Looking further into the data sheets for the 12AX7 and the 12AY7 based on the plate impedance and the plate current vs. plate voltage you need to change the cathode bias resistors when using a 12AY7. The 12AY7 requires 4 to 3 volts at the cathode relative to ground so a resistor value of 2500 to 3300 ohms should be used for both R3 and R8. With R3 and R8 changed you should have approx 3.5 volts at the cathode and with no signal a DC voltage of approx 170 volts at the plate of each triode (pin 6 and pin 1) hope this helps.

[jim p]

My second V5 modification is changing from EL84 to 6V6GT for the output tube. So far with the exception of taking out the 9 pin socket and replacing it with an octal socket the only change is value of cathode resistor R17 to 380 ohms. I am looking into the value of the screen resistor R18 and may increase it to 5 to 10 k ohms. If someone was into a total rebuild with a 6V6 instead of an EL84 you gain 300mA of heater current capability so you could have two 12AX7 tubes and a 6V6GT output tube within the limits of the power transformer. With that you could have input stage, cathode follower driven tone stack, gain stage, volume stage and output tube. Now will start on adding reverb to this amp and maybe a Weber AlNiCo 10S speaker if it will fit.