Ameritron 80b problem

[stargazer19]

I have an ameritron 80b amp after 5 minutes of operation I am losing my drive . left side meter goes to zero on transmition Its
not overheating as my fan and cooling are in operation. I have this unit for 10 years and this is puzzling . Is this a simple fix
or does it require sending back to Ameritron. 73 Peter

 

[NightThumper]

So your plate or grid current go to zero? Are you still reading HV? You’re losing your drive? Do you mean RF output from the AL-80b or from your transceiver?

When you lose your drive is the Xmit light still lit or does it go out?

Brad
KE0XS
South of Pittsburgh

 

[BJ radionut]

Not enough info Peter...which meter function dropping to Zero...Losing drive...might be radio???

 

[nomadradio]

The AL80B from 1991 is a lot different from the one they sell now.

Not quite like a motor vehicle, where the model year is part of what identifies it. The newest versions have a "dynamic bias" circuit. It holds the tube current down until your drive signal arrives, switching it on when needed.

Or so the theory goes. Older versions simply allow a tenth of an Amp more or less to flow through the tube with no drive signal so long as the amplifier is keyed. This makes the tube run hot even before any drive power reaches the tube. The dynamic circuit is intended to reduce that heat stress.

If it fails, no tube current. And if yours is older than the current incarnation, only a zener diode sets the tube's idle current.

This amplifier has been made for decades. Just pinning down which AL80B you have is only a starting point.

73