[Amps] Centurion

[Jim Thomson]

Date: Mon, 20 Jun 2011 12:18:17 -0500
From: Rob Atkinson <ranchorobbo at gmail.com>
Subject: Re: [Amps] Centurion

I have a 10 year old Centurion, one of the pre-black front panel
units.   I have had almost the exact same experience with the h.v.
supply transformer.  After two failures I got the Dahl replacement
(which I don't think is available now) and have had no problems since.
 Without getting into details, I'll say that the experience and
conversation I had, led me to quit purchasing anything else made by
them.  It is a moot point in a way, because I have since become
interested in vintage restoration and homebrewing.  My next amp will
be a homebrew amp.  My Centurion is the only commercially made amp I
have ever owned.   I now run it entirely in AM service at 300 watts.
I have made several modifications--I more than doubled the cooling,
changed the load padding caps to HEC doorknobs, and opened up the
cabinet top for more air flow.  With the Dahl, it is a pretty good
performer on AM.  In fairness I have to admit that there are some
things about the amp's design that I did not appreciate until I became
more knowledgable from studying and planning my own homebrew amp.

73

Rob
K5UJ

##  I fixed a centurion for  VE7IM [sk now]  yrs ago.   that thing was a real eye 
opener.  He bought it,since it had 160m. The tune cap on 160m is way too small, and on 
his, they did not pad ith either.   Their  "fix"  was to run it on 160m..in the real low loaded Q
mode.   When he 1st got it... it sucked full  bore  idle current on RX,  They all did that ! 
How they ever got out the factory door is  beyond me.  The built in metering looks like typ
modutec  junk quality.   In reading the manual... it states  [alomost brags]  that the plate xfmr used
is  rated for  3.5 KVA CCS !!     It further staes that the same xfmr is good for 7000 watts  "IVS" 
[ Int voice service ]     

##  Now that  "IVS"  nonsense is right out of ORR's  books.   What ORR and other's  fail to
grap is that, sure, ssb  with no processing, and barely any alc action, is   probably  10-12% duty cycle. 
The part they all miss is... the amp draws a whack of idle current whn on TX.. even with no drive applied,
which brings up the duty cycle on the xfmr a bunch. 

## Now, while  outright lying to hams  about their  3.5 kva CCS  plate xfmr  is silly at best.... it doesn't
take a rocket scientist to see that no way is there  xfmr  any where close to  3.5 kva CCS.   The centrurion
is one of the "near legal limit"  type of amps  that came out at the time.  It was rated for 1300w  pep out on ssb. 
It's NOT rated for  1.5 kw pep out,  nor will it do even 1.3 kw out on cw.   Dunno what they rated it at on RTTY..
which is trhe usual giveaway.   

## To put it all into perspective, my small  46 lb dahl has various sec taps..and rthe biggest is 2750 Vac @ 1 A  CCS 
=    2.75 kva  CCS.   It's a hypersil core..and weighs  46 lbs.    It's the same size as the one used in any Alpha 77dx. 
Now if folks think they can get 5 kw pep out  from the 2 x hole 77-SX  version..using the same rinky dink 46 lb xfmr...
you are nuts, can't be done. 

##  a 46 lb dahl won't even fit  inside a cenurion as far as I know.  In any event, for those that want to  run 1.5 kw  rtty
out for hrs on end...  you will need a 1500/.6eff  =  2.5 kw  ccs  xfmr.    A  46 lb dahl  barely meets that requirement.
Any dahl that's maxed out willl have a 55 deg C temp rise over a 50 deg C ambient [ that includes internal hot spots] 

##  for the centurion, the dahl replacement is probably in the 22-32 lb range...and will be ample, and reliable for 1.3 kw pep
output service on ssb.    Henry radio went through the same song and dance, with one bad supplier of plate xfmr's  after another. 
Dahl did a roaring business, selling replacement xfm'r  for the  various henry amps, including the 8k ultra.   The ECA brand of xmfr
and choke used in the 8 k was notorius  for biting the dust.    A lot of the small henry amps would blow up when operating CW..
with the B+  switch in the SSB mode. 

later... Jimbo