I have a Centurion and had the same problem tuning for ?max smoke? as suggested
in the manual. One thing I was doing wrong was tuning with the transceiver in
AM mode. Most transceivers operate reduced power on AM and won?t furnish
enough power to fully drive the Centurion and the LOAD control had little
effect. Switching to CW cured the problem. I then tuned up as suggested on an
earlier post (using a dummy load or antenna/tuner with 1:1 swr, use low power
drive and set amplifier TUNE and LOAD controls for max output, then increase
transceiver power to drive grid current into the red zone, use LOAD control to
cut back grid current, re-adjust TUNE for max output then increase drive and
repeat until max drive is used without too much grid current).
The amplifier now is tuned with TUNE and LOAD controls set at around 4, which
is around the numbers suggested in the manual for 3.9 MHz. Also, the linearity
on my monitor scope looks excellent.
Hope this helps someone.
---------- Original Message ----------------------------------
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
Reply-To: Discussion of Ten-Tec Equipment <email@example.com>
Date: Tue, 21 Jun 2005 21:04:23 -0500
>Very good advice! However, I doubt that the fixed output caps are actually
>doorknobs. Probably disc ceramics as the schematic calls for one to be 430
>pf @ 2KV and the other being 330 pf @ 2KV. It appears that the output
>loading variable is 800 pf. I haven't looked inside my amp in years. It
>just keeps on putting out lotsa' RF when called upon to do so.
>----- Original Message -----
>From: "Ken Brown" <firstname.lastname@example.org>
>To: "Discussion of Ten-Tec Equipment" <email@example.com>
>Sent: Monday, June 20, 2005 11:05 PM
>Subject: Re: [TenTec] Centurion loading
>> Hi Mike,
>>> Highest output
>>>is still obtained with the Load control on 10.
>> Most amplifiers do not have enough capacitance in their variable loading
>> capacitor to operate much lower than on about 14 MHz. Fixed capacitors
>> are switched in parallel for the lower bands. An air variable of high
>> enough capacity to work on 160 or 80 meters, without paralleling some
>> fixed capacitors, would be huge, and the amplifier cabinet would have to
>> be much larger to accomodate it. My guess is that in your amplifier one
>> of the fixed capacitors that should be paralleled with the variable
>> loading capacitor has failed, become disconnected, or changed value, so
>> that when you're on 80 meters, your pi-net really does not have enough
>> loading capacitance. Could be a burned contact in the band switch or a
>> loose screw terminal on a doorknob capacitor.
>> Disconnect all power and short the HV to ground before checking it out.
>> DE N6KB
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