[TenTec] Centurion 422 Bias Circuit

Bob McGraw - K4TAX RMcGraw at Blomand.net
Thu Feb 5 15:03:10 EST 2009

My 1996 Centurion shows about 150 ma when in transmit and 0 when not in 
transmit.  I've always thought that to be quite normal and certainly 
acceptable.  Same for CW operation between characters.

I've always had concern for the "newer" amps that claim to cut off the tubes 
between words.  The concern I raise is "at just what signal level does the 
tubes turn on" and how does that affect the low level linearity?  Keep in 
mind that the signal level out of the transmitter has a dynamic range of 
about 60 to 70 dB.  If my math is correct, that 60 dB number translates to 
power values of 100 watts down to 0.0001 watts.  That is about the noise 
floor of most transmitters considering carrier suppression technology.

Bob, K4TAX

----- Original Message ----- 
From: "Carter" <k8vt at ameritech.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Thursday, February 05, 2009 1:41 PM
Subject: Re: [TenTec] Centurion 422 Bias Circuit

> 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.
> 73,
> Carter   K8VT
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