[Amps] AMERITRON AL-80B TUBE ARC / SPLATTER

[Wynand]

Greetings from ZS land.

 

I have an Ameritron AL-80B (single 3-500Z) on the bench that is
uncooperative.

 

HV is fine but once it goes beyond 100mA Grid Current with about 20 watts of
drive the tube starts to splatter (blue arcs inside the tube at the bottom
sounding like an arc welder). This worsens when the plate control is peaked.

 

I also have zero plate current reading (meter not moving in any direction)
and not sure yet if this is a faulty meter board or in circuit component
failure (plate current meter is functioning). All the other meter functions
of both meters are working.

 

The owner indicates that he was operating at around 400 watts when he heard
arcing . he switched everything off and asked me to have a look.

 

There is some signs of arcing on the plate capacitor but not severe.

 

I know my way around high voltage RF equipment and have built quite a number
of my own linear amplifiers, but it is the first AL-80B I have opened.

 

Would appreciate any ideas where to start on this one.

 

73

 

Wynand ZS6ARF