Dan,
I can sympathize with you. I have a Centurion which I purchased used in very
good condition. Had it for a few years and poof went the HV xfmr while the
unit was in standby. The amp was approximately 16 years old when the xfmr
primary opened as you described. $550 later, I had a new TT replacement
xfmr and we were back in business (but a bear to remove and replace). Now, 3
years later, the amp is arcing on 20 mtrs into a dummy load. Have not
checked it out yet, but put my trusty 40 year old SB-220 back on line (with
original caps, etc) and will get around to the Centurion when time permits.
Would be curious to know if anyone else has seen an arcing problem which
immediately causes the Power Output to drop to zero. The problem does not
seem to exist on 40/75 mtrs but is prevalent on 10, 15 and 20 into a Bird
dummy load.
73 and good luck,
Dave
----- Original Message -----
From: "Dan Atchison" <N3ND@aol.com>
To: <amps@contesting.com>; "Jim W7RY" <w7ry@inbox.com>
Sent: Sunday, June 19, 2011 8:13 PM
Subject: [Amps] Centurion
> Well, interesting repair. Yes, the problem was a leaky Q1 on the
> display board. Replaced with a non-descript 2N3904 since I didn't have
> the 2N4124 that was bad. Schematic called for a different transistor
> altogether.
>
> Delving into the circuit also revealed why I had no PTT. Seems if the
> amp detects RF output prior to PTT, then the PTT circuit is disabled. I
> had no RF output, but the leaky transistor had the same effect as
> rectified RF allowing voltage where it was not wanted!
>
> Also found out the step-start circuit is fried. Read that as the power
> resistor is fried. The board it's on is behind the HV transformer so I
> may just leave it alone.
>
> I know many people have Centurions. This one is a 422B, the black (and
> current) faced amp. I've had it almost eight years now and it's been a
> problem child. Early on in its life I lost two HV transformers.
> Tentec had a problem with these and never, NEVER admitted as such. One
> was replaced under warranty, the next one lasted seven months. Both
> failed with shorted primaries. After the second failed, I bit the
> bullet and bought a Peter Dahl and never looked back. I had Dahl
> slightly up the secondary voltage on this one.
>
> This is about the sixth repair on the unit, by far and away my least
> reliable piece of equipment. Even the schematics are wrong -- and I
> bought the amp after it had been on the market already for 15 years or
> so. Even the board screened nomenclature was incorrect on a few boards
> that I noticed while troubleshooting. I may never buy another piece of
> Tentec gear again.
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