vta octal B+ voltage

Hi
I have a vta st 70 octal version and kt88 tubes.As i see the b+ has 350 volts instead of 400.Do you think that i can reduce the value of
the 2k2 resistor between the two capacitors to adjust the voltage?
thank you

kost wrote:Hi
I have a vta st 70 octal version and kt88 tubes.As i see the b+ has 350 volts instead of 400.Do you think that i can reduce the value of
the 2k2 resistor between the two capacitors to adjust the voltage?
thank you

Two things:

a) Reduced B+ will reduce the power-output of the amp somewhat, but it will lengthen the life of the output tubes as well.
b) B+ is directly tied to input (wallplate) voltage. What is your present wallplate voltage?

Put another way... if it ain't broke....

B+ voltage will be inversely proportional to the amount of current running thru the output tubes.
If you turn down the current, the B+ voltage will go up.
The ST70 typically has around 410-420vdc if your AC input voltage is 120vac.
That's running four output tubes at 40-45ma.
If you are running KT88s at 50-60ma each, I can see B+ going down to around 380vdc.
The VTA driver board is designed for 360-380vdc, the difference coming from the ( 2.2K ) dropping resistor.
the board uses 25ma. Use ohms law. A 2.2K resistor will drop about 55v. A 1K resistor will drop around 25v.