[Collins] 30l1 amp.

[Dr. Gerald N. Johnson]

On Tue, 2007-05-15 at 22:04 -0700, ted wrote:
> I have a 30L1 amp, its been working great until today.I was using it today
> and both fuses blew. Replace again and same thing.I figured tube shorted. 
> I thought if I removed tubes and defeated interlock just to see if fuses 
> would blow.They did.!I had  replaced PWR supply board and all components 
> a year ago and has been working just fine.I notice this morning while using 
> amp swr would jump up while on ssb. But if I used lock key on 32s1 swr ok. 
> Well there was some arcing when I moved load control. I cleaned capacitor 
> plates where there was arcing.Would appreciate some input on what to check 
> first. Thank you.
> ______________________________________________________________

There shouldn't be any voltage on the output loading capacitor with no
tubes unless the blocking capacitor is excessively leaky and the output
protection RF choke, L11, is open. So arcing on the output capacitors
should not be what is blowing fuses with no tubes. I suspect some
intermittent connection in the antenna was causing the rises in SWR and
voltage on the loading capacitor and its arcing. That arcing could lead
to lots of plate current.

I suspect power supply rectifier diodes have shorted possibly from the
arc induced large plate current surges though nearly new, though it is
possible to arc inside and destroy the transformer. Checking the diodes
with an ohmmeter will probably show one string with zero resistance, no
forward drop, and no back resistance.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer