[Amps] Triode bias issue

[Wilt Barnum]

Hello all,

I have just finished an HF table top medium power amp using 2X GI 7Bs. In
particular the bias circuit works perfectly drawing the proper idling
current. UNTIL the rf cables are connected i.e input and output, then the
plate volts drop some ( abt 100volts) and the tubes no longer draw idling
current. No malfunction of the HV  supply is apparent and it works fine
with another pair of GI7bs for 6M.

What am I missing?

Thanks, W1IPL Wilt