Yes, I had to replace the bias transistor in my 422b several yrs ago. TT
service still had them. I think a 2n3055 will work.
Andy, W3LI
________________________________________
Bias transistor? I had one go out on my Centurion when it was only a couple
hours old.
73, Duane
Duane Calvin, AC5AA
Austin, Texas
ac5aa@ac5aa.com
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of A R
Sent: Sunday, February 21, 2016 6:52 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Centurion 422b troubleshooting help needed
Forgot to mention that I also meggered grid-to-cathode, plate-to-grid,
plate-to-cathode at 1KV on both 3-500's (cold). Both passed.
73,
Allen--W7GIF
----- Original Message -----
From: A R<mailto:raf_3@msn.com>
To: tentec<mailto:TenTec@contesting.com>
Sent: Sunday, February 21, 2016 5:42 PM
Subject: [TenTec] Centurion 422b troubleshooting help needed
My Centurion 422b amp is sick. With initial application of power, in
selected PTT and STANDBY modes (and un-keyed), the 3-500's are drawing 140
ma plate current (and barely perceptible grid current). Panel MODE led's
indicate proper mode when switched between STANDBY and OPERATE, and the
TRANSMIT led is unlit. When placed in OPERATE mode, and keyed (at the PTT
RCA jack), the TRANSMIT led is illuminated. Keying the PTT input when in
STANDBY mode does NOT illuminate the TRANSMIT led. So, the panel
MODE-indicating led's suggest that mode control functions are OK. The RF
input/output switching/routing is correct for all modes.
Have begun troubleshooting the QSK board, and Filament-AC board (with the
tube bias circuitry), and the HV filter board, but have found that the
componentry on those boards differs from that described in the 422
(no-suffix) manual. Although the manual available on the RKR website is
identified as a 422b manual, it appears to be for a 422 (no-suffix) amp. In
that manual, there are discrepancies between the schematic and board layout
and circuit trace views for the FILAMENT-AC, QSK, and HV FILTER boards. And,
the QSK board in this amp is a p/n 78247, not the 81542 called out in the
422 manual.
Does anyone have a 422b manual, or know if one was ever published...or, even
erratum for the 422 manual?
Has anyone experienced the Centurion failure mode as described, and found
the cause/solution?
Any help is appreciated, and feel free to email me direct, off-list to avoid
cluttering the list.
Thanks in advance, and 73...
Allen--W7GIF
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