[TenTec] Centurion 40 m. oscillation

[Rob Atkinson, K5UJ]

<<<Hi Rob - Agree with most all your comments - As I dig into the Centurion
deeper , there are a lot of corners cut that I would have done differently. 
 >>>

My biggest dissatisfaction is with the power supply.  If your hv xformer 
ever quits replace it with the Dahl plate xformer he makes for the 
centurion.

<<<For instance the meters are lousy - and I am sure for another $20 they 
could
have bought nicely damped meters - but the $20 probably translates into $40
at selling point- which I would glady pay ! The fan is marginal and for
virtually zero extra cost they could have almost doubled the cooling with a
fan from the same vendor that fits the exact same space and mounting ( their
answer to this is that then they get too many complaints about noise) - My
25 year old L7 handles that with a 30 cent thermostat in the airflow and a
30 cent resistor.>>>

I think they were really responding to requests for a quiet amp.   Many of 
the  Centurion eham reviews comment positively on how quiet it is.   I guess 
it isn't an issue for light duty cycle modes.  Like you, I prefer more 
cooling.  I'm experimenting with ways of moving more air through the rf deck 
without leaving the pins undercooled.

<<<But it seems TT design philosophy is to do it as cheaply as it can 
possibly
be done in some respects , but in other areas , it looks like they made it
about as hard on themselves as possible! But I guess that comes from years
of making my living designing RF stuff to make a profit. Everybody has their
own approaches.>>>

I like the led wattmeter, but i'd much rather have the aforementioned dahl 
plate transformer, but that probably costs more than a qsk circuit and led 
wattmeter which are marketable.
I originally thought these were nice accessories, and I do find the 
wattmeter convenient, however I have learned to appreciate a stout power 
supply, and lots of forced air.

<<<I have not measured the input swr across all the bands with a MFJ , but 
the
Orion internal SWR (subject to some suspicion)  -shows better than 1.4  over
the cw portions which is all I use 99 percent of the time. I do notice some
shift in swr at low power (300-500 watts out ) versus  1000-1300 watts out
but I think thats to be expected. The amp runs with something around 2800
volts fully loaded >>>

with the stock plate xformer, mine was at 2.8 or 2.9 kv (as measured on the 
f.p. meter) and sagged to 2.5-2.6 kv upon being keyed.   With the dahl I'm 
getting 3.1 kv down to 2.8.  at ~1.2 kw out I'm seeing 2.6 kv and 700 ma Ip 
(on 40 m.).  this is when driven by a Mk V.  With a 200 w. PA turned down to 
100 w., the Mk V doesn't fold back with 1.5 vswr.

<<<RE:  Varying the length of exciter-amp jumper is an okay solution
if you spend your entire ham existence operating on only one band.

As I said , at least right now on CW , it works OK - just for grins when I
can't find anything else to do , I think I will try a even longer length to
see what happens - I suspect at the "wrong" length , even longer , the phase
angles will add up wrong again. Since its so easy to drive to a KW which is
about all I usually run , I toyed with  putting in a 2 or 3 db resistive
pad - (would probably help SSB IMD too )>>>

In my experience, you will chase a moving target.   An okay length on one 
band will cause problems to pop up on another.   Not knowing what YT1VP 
wrote, I didn't know what was going on.   I only vaguely knew that changing 
the length of the feed between the exciter and the amp made a difference and 
that there must have been some weird reactance in the line.   I kept making 
the jumper shorter and shorter, not wanting to have to adjust another 
matching network manually.  I finally gave up and started using rigs with 
either an autotuner or a PA that didn't care.

<<<99  percent of what you say - you are preaching to the choir !>>>

I can't take credit for that stuff--it's way over my head--give credit to 
YT1VP

<<< I had fun working with the guy who started Gates (Harris )  transfer 
into
solid state and who built the first 100 KW switching mode transmitters . >>>

was that hilmer swanson?

73 hank

rob/k5uj

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