# [TenTec] Centurion 422 Bias Circuit Solved

Bob McGraw - K4TAX RMcGraw at Blomand.net
Thu Feb 5 20:45:09 EST 2009

```Can't see how you get that date/data from those numbers.

My translation says for SN 5B10053:
5 = May
B = Separator
1 = 1st production for May
005 = 5th unit
3 =  1993 or could that be 2003?

Don't see how you get 34 out of that or 9 as the year of manufacturer since
the SN doesn't contain those numbers.

73
Bob, K4TAX

----- Original Message -----
From: "jack" <jfriend31 at comcast.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Thursday, February 05, 2009 7:04 PM
Subject: Re: [TenTec] Centurion 422 Bias Circuit Solved

> according to the tentec code for serial numbers:
>
> amplifier s/n 5b10053
>
> means:
>
> 5 = may
> b=separator
> 1=production run for that month
> 034 =unit number for that run
> 9=year of manufacture
>
> jack
> ak7o
>
> ----- Original Message -----
> From: "K0BX" <k0bx at arrl.net>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Sent: Thursday, February 05, 2009 5:44 PM
> Subject: [TenTec] Centurion 422 Bias Circuit Solved
>
>
>> Last night I wired up the cable for my Icom IC-756PROIII to do break-in
>> CW.  CW keying to the 422, 422 to the rig.
>>
>> So let me try to explain what I was looking for.
>>
>> 1.  In SSB, if you key the mike with no audio, you get a plate current
>> of about 100 to 150 ma, 1/2 way between 0 and .2 ma.  This is normal for
>> SSB.
>>
>> 2.  In CW, using breakin, the older models of the 422 would put the amp
>> in transmit and draw the 100 ~ 150 ma when it was in between keying.
>> Like you are waiting for the DX station to say QRZ again.
>> This would cause a lot of heat from the tubes.  See the QST Review on
>> the 422 from 1991.
>>
>> 3.  What I found is the later,  models of the 422 that are greater than
>> the one in the QST Review does not do this.  Instead there is no idle
>> current in breakin during the pause for QRZ.
>> I guess I should have waiting to ask the question until I had the wiring
>> completed.   I had this heat problem with my Drake L-7 and Ameritron
>> QSK-5.  It would lock the amp in xmit and just go around it for receive
>> but you
>> could see the 150ma on the plate meter.
>>
>> The last question I had was about the serial number and the date it was
>> built.  From what I have found is that S/N with 'A' in it was before
>> year 2000.  The last number of the S/N is the year.
>> So mine would have been built in 1992 and was the 004th on of that
>> production run.  Any ideas if I am close or not??
>>
>> Thanks for all the inputs
>>
>> Joe K0BX
>>
>> Carter wrote:
>>
>>>k0bx at arrl.net wrote:
>>>
>>>
>>>> I just received a 422 Centurion. My question is: How do I determine
>>>> if the newer Bias circuit is installed?? This circuit cuts off the
>>>> bias when the rig is in transmit but is in idle.
>>>>
>>>>
>>>
>>>I think you sort of answered your own question.... if it's in transmit
>>>but idle, plate current should be zero. Going back 10 or 12 years ago,
>>>my bias board failed and then there was about 300 ma of plate current in
>>>idle. You could take it out of its case and check the revision suffix on
>>>the board (see below). Otherwise, I don't believe there is an easy way
>>>to tell.
>>>
>>>I had the original bias board that failed; as of ten years ago, I
>>>believe TT  had a -B and then a -C rev of the board.
>>>
>>>Note: all of the above is subject to the vagaries of my memory.   <grin>
>>>
>>>
>>>
>>>> QSL review from 1994 S/N 10A10091 had the old bias circuit and they
>>>> indicated that the newer one had the modifiy circuit. My S/N is
>>>> 80A10042. But no date of purchase was indicated in the manual. Any
>>>> ideas? Any ideas on when the 80A10042 was built?
>>>>
>>>>
>>>
>>>
>>>It's a nice amp! Enjoy it.
>>>
>>>73,
>>>Carter   K8VT
>>>
>>>_______________________________________________
>>>TenTec mailing list
>>>TenTec at contesting.com
>>>http://lists.contesting.com/mailman/listinfo/tentec
>>>
>>>
>>>
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```