[Amps] sb220

[Tom W8JI]

> Hello.i am a SB220 owner.i just got it to work.clean it 
> upp and all. after 4 years.but somthing is wrong i get 550 
> W output?... and when i try the 3-500z each in single use 
> i get 550w out on a single tube ?.and when i install then 
> both i still get 550w..someone?


In grounded grid the gain does not change as much as we 
expect when we parallel more and more tubes.

This is because in a grounded grid amplifier the output is 
in series with the input and the impedance ratio mostly 
determines the gain.

When you add tubes you have to increase drive to have 
significantly more output.

You might have another problem, but don't expect to see 
double power with double tubes. It won't happen in grounded 
grid. When you install both tubes do they both appear to 
show similar color on the anode when operating? What is your 
power meter and drive power? What is the HV?

The SB220 was designed to run about 600W output on CW, and 
1200W PEP on SSB output. It is a 1kW CW input, 2kW PEP SSB 
output amplifier.

73 Tom