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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