[TenTec] Centurion 422b troubleshooting help needed

[A R]

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 at msn.com> 

To: tentec<mailto:TenTec at 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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