[Amps] 2 x 4-250A Amp

[Mark Kachel]

I bought a home brew amp with 2 x 4-250A tubes on ebay. Nicely built but it 
is grounded grid.

The filament transformer is 10 volts with no center tap and the two five 
volt filaments are wired in series. The B- is thru a meter to a resistor 
across the filaments.The article with the amp suggests the bias is for class 
B operation.

I want to convert the amp to a tetrode circuit running AB1. My first 
question is the B- point. I will use the same filament transformer and I 
want to know if connecting a meter between ground and the connection between 
the two filaments in series will work OK. I can't see why not. But you folks 
know a whole lot more about this stuff than I do.

I need to build a power supply and from what I can see, using the tetrode 
board from IFWTech / G3SEK will make life a lot easier. I was planning on 
getting the screen bias voltage for the tetrode board by taping across the 
lower caps in the power supply. Not much current is drawn so I don't see 
that this will cause a problem. What do you think?

Mark, NØOKS