SB-401 driver capacitor shorted - what happened?

[Robert Myers]

I was tuning up my SB-401, and the driver tuning capacitor plates
shorted somewhere (there was some misalignment between the front panel's
control shaft and the capacitor's shaft that cause a slight 'warping
effect' during the turning).

 

I had the HV and the screen voltage removed from the 6146's at the time
because I was aligning it, and going through all the steps.  There is a
part where you connect an RF probe between the solid bus wire joining
both pin 5's between the 6146's, and you maximize voltage (this is
before you neutralize the finals).  I was getting about 50 volts (RF
rectified DC) before the arc --- and that was a solid steady voltage.
Now I can only get about 25 volts, and it is a 'flaky' voltage that
drifts lower and lower about 1 volt per second.  It settles at about 12
volts.  This happens on all bands.  None of the coils were burned by the
short, however - and all the resistors that would be in that path of
high current seem OK.

 

Does anyone have any idea what may have been affected?  Has this
happened to anyone?

 

Thanks,

-- Rob VE3JQL


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