I got a similar case by using a diode instead of resistor for the -B, the
shorted diode indicated gi current without any excitation RF on a grounded
grig amp with 2x 3-500 ZG were keyed.
Good luck
va2am Réjean
On Tue, Jul 14, 2015 at 8:21 PM, Dave Hachadorian <k6ll.dave@gmail.com>
wrote:
> 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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--
*Réjean Léveillé*
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