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Re: [TenTec] Centurion 422b troubleshooting help needed

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Centurion 422b troubleshooting help needed
From: Gary J FollettDukes HiFi <dukeshifi@comcast.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 21 Feb 2016 21:25:01 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Darned AUTOCORRECT!

“overcurrent”, NOT “overcorrect”!



> On Feb 21, 2016, at 9:17 PM, Gary J FollettDukes HiFi <dukeshifi@comcast.net> 
> wrote:
> 
> This transistor sounds like a likely candidate as the amp is acting like it 
> is keyed regardless of the state of the keying line.
> 
> Question is, why did it fail? A 2N3055 is good for 15 to 20amps so 
> overcorrect is not a factor. Is there adequate transient suppression around 
> this transistor to protect it from voltage transients?
> 
> Just curious…
> 
> Gary
> 
> W0DVV
> 
> 
>> On Feb 21, 2016, at 8:03 PM, Carter <k8vt@ameritech.net 
>> <mailto:k8vt@ameritech.net>> wrote:
>> 
>> On 2/21/2016 7:42 PM, A R wrote:
>>>   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.
>>> 
>>> 
>> 
>> Sure sounds like the bias transistor on the Filament-AC board. Been there, 
>> done that.
>> 
>> Let us know how you make out...
>> 
>> 73,
>> Carter   K8VT
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