[AMPS] Alpha PA 77D

[Rich Measures]

>....... the plate tune vacuum cap has about 200 little
>pitts in the internal element. I assume it was way out of tune a few
>times ...
I wouldn't bet on it.  
>...and once it became pitted the arcs were easier to get started.
>Anyone know if this item is easly found? The book said it was a 400pf at
>7500 volts.
Jennings will sell you one [408 292 4025].  However, I doubt that a new 
unit will correct the reason that the original cap. was arcing.  
>  The next item of interest was the band switch. It looks like the
>contacts are still making but some arcing has taken place. Looks like it
>might have been on 10 meters at the time??? 
Arcing at the 10m contacts is usually an indication of intermittent vhf 
oscillation--a condition which Messrs. Erhorn and Rauch say can not 
happen.  If it were my amp., I would conduct a sputtered gold test on the 
8877 with a high-pot tester. I have tested a number of 8877s that died in 
77s due to gold sputtering.  I currently have a decapitated one sitting 
on my desk.  It might be a good idea to decrease the vhf-Rp of the 
anode's vhf parasitic suppressor.   
>I might as well replace that
>too. 
...snip 
>  It has QSK with a vacuum relay in the output. 
however, the 26v vacuum relay closes too slow for some modern radios.  
The speedup-solution is to raise the relay's coil source from 50v to at 
least100v and increase the series R that limits the relay's coil current 
to 80mA. 
Rich---

R. L. Measures, 805-386-3734, AG6K   


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm