[Amps] AL-80B trouble

[R L Measures]

On Aug 25, 2006, at 9:07 AM, Roy Koeppe wrote:

> Stated;
>
>
> "...SYMPTOM:  With the standby  switch in standby, band-switch set for
> 80M, AC power applied to Amp, the meters  read ~2700Vdc (normal is
> ~3000Vdc), 150ma Ip, and the Ig is showing a negative  draw.  The Ig
> meter buries itself to the  left.  After 2-3 minutes in this   
> condition,
> the plate is glowing reddish orange.   With the standby switch placed
> into operate, RF applied from the  exciter, the exciter complains of
> High SWR and there is no RF power being produced  by the Amp.  With  
> the
> band-switch placed  in any other position, the same symptoms apply.
>
>       ASSUMPTION:  The  3-500ZG has a short,

Agreed.

> and or the tube is not
> receiving the proper bias voltage  during off periods .  The glowing
> while  in standby is due to the current draw across the plate;
> dissipating ~400W. (etc.)"
>
>
> Yes, this is commonplace. The tube shorts internally from grid to
> filament.

Roy K.  == The hot filament helix apparently bends horizontally from  
EMF during a burst of grid-current.  IMO, this occurs during an  
intermittent VHF parasitic oscillation. Do you have access to a  
dipmeter?
>
> 73,    Roy      K6XK
>
>
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R L MEASURES, AG6K. 805-386-3734
r at somis.org