[TenTec] Centurion 422 Bias Circuit Solved

jack jfriend31 at comcast.net
Thu Feb 5 20:04:41 EST 2009

according to the tentec code for serial numbers:

amplifier s/n 5b10053


5 = may
1=production run for that month
034 =unit number for that run
9=year of manufacture


----- 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?
>>Probably ask TT.
>>It's a nice amp! Enjoy it.
>>Carter   K8VT
>>TenTec mailing list
>>TenTec at contesting.com
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