Tnx Peter/Carl/Bill,
Tube is now on with heather/blower, let's see what happens next Friday ....
73's Carel, pc5m
-----Original Message-----
From: peter chadwick [mailto:g8on@fsmail.net]
Sent: woensdag 21 augustus 2013 18:08
To: Carel pc5m
Subject: RE: [Amps] 3cx800 flashover ?
Try running it with filament volts only for 48 hours - apparently the getters
on the ceramic tubes are activated by cathode heat.
73
Peter G3RZP
========================================
Message Received: Aug 21 2013, 05:03 PM
From: "Carel, pc5m" <pc5m@xs4all.nl>
To: amps@contesting.com
Cc:
Subject: [Amps] 3cx800 flashover ?
Hi, I need some advice of the group if this 3cx800 is beyond revitalization.
Working on an old SSB electronics 70cm PA with a single 3cx800 in grounded
grid configuration. Original bias/control circuit was replaced with g3sek
triode board. PA has been out of service for maybe 10 years or so.
When applying heather and Ua and cut-off bias all fine, no flashes, no
currents
Gradually lowering the kathode zenervoltage towards 8V the anode current is
increasing normally till approx 50mA at that point I hear internal tube arcing
(I think) and upon lowering the cathode voltge even more the over current
protection suddenly jumps in (set at 800mA or so).
Question: is it normal to get internal flashover only at non-zero anode
current ? (at 0 mA no flashovers!) Or do I have maybe another issue ? low
frequency oscillations ?
I did replace the active zener config for a brute force string of diodes (8
in a row or so), same phenomena .
Anything I could do more before trashing this 3cx800 ?
Tnx, Carel pc5m.
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