Bob:
Thanks for the information. My 2003 Centurion's manual has no statement
like the .jpg you provided, I assume, from your manual. I checked
before I sent my original email. Interesting that TenTec replaced your
friends transformer after 3 years, but didn't replace mine after 15
months. I believe your vintage Centurion did have a TenTec wound
transformer - as I believe they used to do all their windings in house
until their "winder" left or retired.
While I was not bashing the Centurion, I was ticked that TenTec never
came clean. Indeed, they never contacted me after receiving the
amplifier to tell me they wouldn't cover it and they never contacted me
that a tube was "bad," nor did they contact me when the amp was
finished (repaired). I didn't know they had even worked on it until I
received an invoice in the mail telling me the bill was $700 and to pay
before return shipment. No communication at all. Had I known that they
would not cover it under warranty (previous phone calls had led me to
believe they might), I would not have had it repaired since I already
knew what the problem was. Reading all the nice things about TenTec
service I would have thought there'd be some give and take, but to go
ahead and fix it without approval or further discussion seemed
arrogant. Yes, they had my email address (two to be exact) and my cell
phone number. I think you can understand how I might have been upset.
I have had two other failures in it in four years. One caused by a
critter getting into the amp and finding a nice spot between the lower
connection on the HV RF choke and ground. Obviously, this is not
TecTec's fault. The other was a cracked feedthrough insulator between
the HV power supply and the RF deck. Apparently when it was installed
it was torqued too much and cracked, eventually creating a carbon path
to ground. All it took was the 10 Ohm(?), 25 Watt resistor/fuse and of
course the insulated feedthrough. Both of those failures darn near gave
me a heart attack when they went!
All this being said, I like the Centurion (see my review on eHam). I
run mostly CW and mostly QSK with the amp, originally with an FT-1000D
and now an FT-2000. The QSK loop works great and I am told that no one
can tell the difference in keying between barefoot and amp other than
strength of signal. It is a keeper regardless of my experiences -
experiences that others may see.
73,
Dan -- N3ND
-----Original Message-----
From: Bob McGraw - K4TAX <RMcGraw@Blomand.net>
To: n3nd@aol.com
Sent: Sun, 5 Aug 2007 11:52 pm
Subject: Oh? Centurion PS
Â
> Dan:Â
>Â
> I appreciate your candid comments and personal experiences. We each
haveÂ
> personal experiences from which we speak. Mine are different than
yours.Â
>Â
> In March 1996 I purchased my Centurion from Tentec. From that manual
> comesÂ
> the attached JPG which describes the HV power transformer. The
amplifierÂ
> has seen typically 5 or more hrs use per week on the various nets,
75M andÂ
> 20M, to which I participate. The amp is some 11+ years old. Now lets
> see,Â
> 11 x 52 = 572 weeks x 5 hrs = 2860 hours of usage. All with the
originalÂ
> transformer and the original tubes.Â
>Â
> As to power output, it always has been run on a solid 230 volt
service, > andÂ
> never a 120 volt service. As I recently had the amp on the service
benchÂ
> for its annual cleaning, inspection and fan lubrication, the power
outputÂ
> was measured using my Bird 43P meter which I purchased new and a Bird
2500Â
> watt slug which I also purchased new solely for the purpose of
working on > myÂ
> ham equipment. Realizing that the Bird meter has a accuracy of +/- 5%
FS,Â
> the amp on 20 meters, driven by my Omni VI Plus will deliver power
into aÂ
> 50.5 ohm load and as indicated by the Bird 43P just described, showsÂ
> slightly over 1500 watts. This is with a PA current of 0.8 amps and a
> gridÂ
> current of 260 ma. Now, Tentec rates the amp at 1300 watts output.
Why > isÂ
> mine 1500 watts? Well for one thing the Tentec rating is the power
out ofÂ
> the amp less the driving power. My measurement is total power output
> whichÂ
> is amp power out plus drive power. One other measurement which I findÂ
> useful to make is a power/bandwidth measurement. The amp measured
11.1 dBÂ
> of gain. That very closely concurs with the power values measured. I
didÂ
> observe that the gain of the amp, and thusly the power output does
varyÂ
> somewhat from band to band. Worst case of course is 10 meters
followed byÂ
> 160 meters with best case being 20 meters.Â
>Â
> Now for a bit more math. Tentec states and I have measured 3100 volts
noÂ
> load and 2600 VDC on the PA under a 0.8 amp PA load. That is then
2080Â
> watts DC input. At an efficiency of 65% which nets 1352 watts output.
> AddÂ
> the 100 watts of drive and one has 1452 watts of output. Considering
thatÂ
> accuracy of the Bird meter, 1500 watts indicated is well within the >
accuracyÂ
> of the measurement system.Â
>Â
> As to Tentec bashing, I'm not in favor of it. But when someone posts
aÂ
> message that says the BLA BLA amp will run circles around the
Centurion,Â
> factually and technically it isn't so. They of course are relating
theirÂ
> experience but it is not or was not backed by technical facts. All
thoseÂ
> persons then that may read the reflector likely gets the idea that
theÂ
> Centurion has a "light weight" power supply because "so and so" said
so.Â
> Just because they said it doesn't make it so. Yes, I've seen the
commentsÂ
> on the HV transformer failures and have always been puzzled as to
why. IÂ
> have a friend that had a HV transformer failure about 3 years after
heÂ
> purchased the amp. Tentec replaced the transformer for NC! Hey,
what'sÂ
> there to complain about? Other than it did cost him the shipping to
andÂ
> from the factory.Â
>Â
> The negative side of the Centurion in my opinion is the fact that it
uses > aÂ
> voltage doubler HV supply. The other compared BLA BLA amp uses a FW >
bridgeÂ
> rectifier. Without question, the FW bridge circuit will give betterÂ
> regulation no load to full load as compared to a FW voltage doubler >
supply.Â
> But at the time of the Centurion introduction, the Heath SB-220 was a
veryÂ
> popular amp and it used a voltage doubler HV supply. So why not
follow aÂ
> winner? I had a SB-220 back in the late '70's too. It suffered about
theÂ
> same HV regulation ills.Â
>Â
> At the same time the other referenced amp claims, per spec on their >
website,Â
> to run 3600 volts no load and 3100 volts rated load. According to the
> tubeÂ
> data that I reference, the manufacturer recommends a maximum of 3000
voltsÂ
> for grounded grid service. I therefore view the other amp to be
designedÂ
> and operated outside of the tube manufactures rating. This too is
thenÂ
> risky and of poor design in my book.Â
>Â
> As to the Peter Dahl transformers, they are good no question about
it. > TheyÂ
> originate from a company that makes transformers and little else.
They > haveÂ
> vast experience, knowledge and a very well equipped facility to buildÂ
> transformers. At the same time, for what ever business reason,
initiallyÂ
> Tentec elected to build their own. This was done for a few years and
thenÂ
> perhaps they realized that the cost and productivity for low quantityÂ
> transformers was not effective and they elected to purchase
transformersÂ
> elsewhere. Likely for less money than the Dahl transformer. Business
isÂ
> business and bottom line is bottom line. As they say "that's water
underÂ
> the bridge and it's too late to paddle up stream". I suspect that
TentecÂ
> will drop the amplifier line as it is not adequately profitable. I >
suspectÂ
> to see all amp manufacturers increase prices as the cost of copper isÂ
> rapidly increasing along with other materials cost going up. I see
that > theÂ
> demand for an HF amp is in a downward trend and will continue to do
soÂ
> largely due to the vast number of hams that are locating in
propertiesÂ
> covered by CC&R's and many homes now being built on zero lot lines.Â
> Although antenna restrictions are being limited or removed, high
power > justÂ
> doesn't get along in dense populated neighborhoods.Â
>Â
> One other story from the K4TAX QTH. I acquired a RCA BTA 1R1
broadcastÂ
> transmitter with the intention of using it on 160M and 75M AM. Yes, I
doÂ
> operate a good bit of AM. Well the HV transformer was found
defective.Â
> According to the station owner and their engineer, it was a Peter
DahlÂ
> transformer that was purchased by the station to replace the originalÂ
> RCA/Thorsden HV transformer which failed after about 5 year of
service. > InÂ
> order for me to restore the transmitter to "like original" I spent
may > hoursÂ
> cleaning, repairing, and general maintenance including purchasing a
newÂ
> Peter Dahl transformer for the HV supply. I can tell you, that set my
hamÂ
> radio budget back a good bit. That transmitter, all 1400 lbs of it,
sitsÂ
> today in my shop along with the Heath Apache and HQ-170 A receiver.
Not aÂ
> bad AM station.Â
>Â
> Hopefully, this is not too long winded {although I've said I work AM}
andÂ
> that this expands my thoughts and findings on the Centurion light
weightÂ
> power supply issue.Â
>Â
> 73Â
> Bob, K4TAXÂ
>Â
[Image Removed]
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