Thanks to everybody who answered.
I think that what Dave wrote could be very probable: next weekend I will
open the PA and let you know what I will find.
The HV comes with a coaxial cable, but I think that cable and connector
have two concentric paths (B+ and B-) and screen as safety protection
connected to ground, otherwise the B- would be connected directly to
ground and it would be impossible to measure grid current.
Thanks again and 73
Guido, k2bcp
Il 15/07/2015 02:21, Dave Hachadorian ha scritto:
This type of thing can happen if B- and ground are tied together.
There should be a beefy diode between B- and ground. Sometimes this
diode can short if there is a high current glitch event. Also, the
plate current meter may have blown open during such an event.
Dave Hachadorian, K6LL
Yuma, AZ
-----Original Message----- From: Guido Tedeschi
Sent: Tuesday, July 14, 2015 1:47 PM
To: amps@contesting.com
Subject: [Amps] Triode grounded grid amp strange failure
Hello All,
a homebrewed two chassis 3CX3000A7 GG amp of a friend has this
strange failure when switched on TX:
- no more current on plate meter
- 200 mA of grid current with no signal
- some power out (few hundred Watts) when driven with 40-50 W, to limit
the grid current to less than 500 mA, but still no current on plate meter
We don't have any schematic diagram so, before opening the amp and
troubleshooting, some suggestions to begin would be very appreciated
(hoping that the tube will not be the culprit...).
Thanks and 73
Guido
K2BCP
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