• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Operating point of GM70

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Administrator
Joined 2004
Paid Member
I'm running at 1kV, 100 - 120mA and 7K plate load. I get roughly 20W output.
Long ago load line calculations indicated 20W @ 7K, and maybe 25W @ 6K if I recall correctly, I also considered a 5K load line, but decided the added power came with too much distortion attached. I choose the higher impedance in order to reduce distortion. Many people have run them into loads as high as 10K with good results.

I'd say at minimum the output transformer insulation should be rated for continuous operation at a combined 2kV - 2.5kV ac+dc, this will prevent failure. (My amp swings 1kVac p-p with 1kVdc, and is insulated for 2.5kV. ) And please ground the secondary for safety.

Over time I have come to prefer the graphic plate version, although others prefer the copper plate version of the GM70.

For the 1kV supply I used solid state FW bridge rectifier with silicon carbide rectifiers into CLCLC filters.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.