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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Ten-Tec Centaur Help

Reviews Summary for Ten-Tec Centaur
Ten-Tec Centaur Reviews: 31 Average rating: 4.8/5 MSRP: $749
Description: Full QSK 600W HF linear amplifier
Product is in production.
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KR9D Rating: 5/5 Apr 15, 2008 13:36 Send this review to a friend
A significant improvement on the AL-811 for only a few more $  Time owned: 0 to 3 months
I recently purchased a used Centaur for my primary operating position, so I could move my AL-811 (which has been trouble-prone) to a secondary operating position.

The seller of the used Centaur I bought warned me that the QSK/PTT switch had a bent handle, and I foolishly tried to straighten it. Of course, it broke, and I replaced that and the bypass switch with mini-toggle DPDT switches from Radio Shack. They look the same as the (admittedly low cost) originals and they work. I may order something a bit nicer from Mouser in the fullness of time.

Working on the Centaur is a pleasure. It comes part easily, unlike the AL-811 (which I also own), and the panels can be removed without unsoldering anything. Just like the Omni V. A lot of disassembly is required to remove the front panel, but it's all obvious and easy to reassemble, especially compared to the AL-811.

Yes, the fan is noisy. But I never felt much warmth coming off those Chinese 811's, even after heating up my dummy load quite a bit. And I barely heard it at all when wearing headphones, as I routinely do.

The Centaur has a forward power meter, which the manual claims is only calibrated in the 400-600 watt range. I doubt that it is calibrated at all. I was reading 600+ watts consistently on 80-15 meters and 500 on 10 meters into a dummy load, with grid current well below 125 ma and plate currents well below 500 ma even key down. I measure output using an Ameritron AWM-30 true peak-reading power meter, which also allows me to tune up using CW dits instead of key down.

Previous reviews and statements in the various Ten Tec archives reveal many who were unable to get the full rated power out of the Centaur. I think I know why. The power meter just plain reads low. When putting out 600 watts key down (as measured by the AWM-30), I was also seeing over 600 watts on my Ten Tec Model 229 tuner's power meter, but only a little over 400 watts on the Centaur's power meter. I wonder if those who didn't think they were getting full power really were.

The Centaur tunes quickly and easily compared to the AL-811, and runs at rated power with lower grid and plate currents.

Something I can't explain (based on the usual descriptions of 811's in grounded-grid AB configuration), but that agrees with the ARRL review, is that it reaches rated power at an exciter power of 80-90 watts, instead of 55-60 watts as with the AL-811. This is a good thing, in that it largely prevents an overdrive-based Big Mistake. Tuning is easy: Set RF Power on the transceiver to the middle of the dial, send a string of dits, tune the amp for maximum power, turn the RF power up to about 9 on a scale of 10, and tune for maximum power on another string of dits. Keep an eye on grid current, keeping it below 125 ma. Plate current should be below 450 or 500 ma, but may be a bit higher during tuning. Reduce drive if desired. The Centaur tunes in half the time of an AL-811, at least with my hands on the controls.

The circuit design seems safer and a stock AL-811. For example, the bleeder resistors are in pairs and paralleled. Ditto for the parasitic suppression resistors. The design resists a serious fault from a failed resistor. The execution is considerably more robust. The voltage rating of the power-supply caps is 2200 volts against a high-voltage supply of 1800 volts. On the AL-811, the caps are rated to 1800 volts, which depends on everything being perfectly matched to keep one of the caps from experiencing a bit higher voltage than the rating. The design includes fault protections such as prevention of hot-switching, which the AL-811 does not have.

The transformer in the Centaur is substantially beefier (and heavier) than the transformer in the AL-811.

I could not find a way to overdrive the tubes, except I suppose by running it at full exciter power in an untuned state. The notion of putting 572b tubes in this amp just for improved forgiveness seems really unjustifiable. I'm leaving the Chinese 811's in it until I have a reason not to.

And then there's the QSK. I am not a CW operator, but I could easily hear the band between the dits at 30 or 40 WPM. It works so well it makes me want to work on those CW skills. The Centaur provides a standard keying loop with the option of a direct PTT input. Using a transceiver with a keying loop, the setup is easy and works in all modes. QSK is possible without such a transceiver, however, by hooking the key up to the Key In on the amp and running the Key Out to the PTT input on the transceiver. For phone, supplement this arrangement with a line from the amp control relay output of the transceiver to the PTT input, and use the PTT/QSK switch on the amp to switch between the two modes.

The amp provides ALC, but with the high input drive requirement I observed, I don't see much need for it. In fact, if the transceiver drive is set to provide 600 watts (properly measured) of amp output key down, then ALC is not needed.

Ten Tec's manual is typical of Ten Tec: Informative and complete, with a schematic, board layout, and operating description of every board.
G0BYH Rating: 5/5 Feb 11, 2008 02:42 Send this review to a friend
No regrets  Time owned: more than 12 months
Bought this amplifier approx' 7 years ago and apart from one 811A tube failure (My fault) and one scale lamp blowing it's never given any problems. Upgraded it to 572B's just to overcome some of those "Tune Up" mistakes HI, and it loafs along at 400w with just 50w of drive from a TenTec ORION, mainly gets used on RTTY (200w) and SSB.
If you are looking for a mid power range amplifier and can find one second hand would definitely recommend this one.
KC2HTV Rating: 5/5 Feb 8, 2008 19:18 Send this review to a friend
Top Shelf  Time owned: more than 12 months
Running for 1 year now completely stock with an FT-1000MP driving it... Averages 600 plus on 220vac and around 450 on 120vac... Love the mini hurricane they call a fan... Absolutely the best $400.00 I have spent in sometime... After 2 Ameritrons I finally have an amp that is damn near bullet proof with a very mellow audio... I just became a Ten Tec fan... Just need an Omni C to drive it for effect but will probably end up with an old rig first to get the feel of their operation... 811's are inexpensive and have a very sweet audio... Highly recommend it if you can find one...
WA3OFR Rating: 4/5 Sep 15, 2007 17:52 Send this review to a friend
Expected more...maybe its just me?!  Time owned: 3 to 6 months
I'm a die hard TT fan, so when it came to boosting my Omni V, it was the Centaur or Centurion...(QSK or bust)..any other amp would be heresy!! After reading the reviews, settled on the Centaur for value ($600), power (110V) and modest tube cost. Mine was "mint" - but 811's blew up after the 10'th worries, I'd read the 572B's were the way to go anyway! Retubed ($170) and expected to be "loafing at 600W" like every other reviewer in eHam...but I struggle to get above 400W (using external meter). After a few months a cap on the plate board popped so off to TT for a "tune up". They replaced the caps, coils, tightened some loose connections and sent a data report that >500W achieved on all bands. ($215) They suspected a parasitic osc. is what took out the caps..and suggested that this amp prefers an 8' (or so) cable on the input. Hmmm.. c'mon TT... sounds like its conditionally stable ..not what I would have expected. Its still fussy - can barely get above 400W (even into a dummy load). After running 100W for 38 years ...400W is a big help, but mine isn't loafing like the others! The fan is annoying as advertise...especially pulling weak CW sigs out.. I will have to mod to top mounted muffin fans or slow it down otherwise I'll have a notch in my hearing!! I'd probably rate it a 3, but it got me BS7H before it exploded, and thats what I bought it to do, so I'll cut it a little slack!
N7WR Rating: 5/5 Dec 5, 2005 18:56 Send this review to a friend
XLNT  Time owned: 0 to 3 months
Haven't owned it long but I was fortunate to buy one in absolutely mint condition. Inside and out it looks like it just left the factory. Not a scratch on it. Has been re-tubed with 572B's. Easy 600 watts as promised. I do not find the fan noise objectionable. In fact, the way I have it placed on the operating desk I really don't hear it any more than I hear the occasional fan noise on the IC 706 MKII G. Nice size and adequate output for an amp that will run on 110 vac and loaf at 500 watts peaking, in some cases, at about 700.
KR3DX Rating: 5/5 Feb 13, 2005 19:23 Send this review to a friend
BOMB PROOF  Time owned: 0 to 3 months
I got this amp 3 weeks ago from a local ham friend. A few years ago, one of the tubes shorted. I took a look at the amp for him, the primary line fuses were blown. I replaced the shorted tube and the fuses, the amp worked just fine, NO other damage. How many other amps could survive a flashover with nothing more than blown line fuses? (The tube was probably gassy, I don't know since I wasn't the op, hi) This is the tiger tank of small tube type amps. Big, beefy transformer. Buttery smooth vernier tuning. I have installed 3 Svetlana 572B tubes to replace the non-matched 811A tubes. I like the fan, maximum cooling is the way to go, in my opinion. I have run it several times on AM rag-chews, it gets warm, not hot. All of the components seem to be of good quality, and the construction and design are typical Ten-Tec excellence. Full QSK for CW ops too. I agree, it's a pity that tube availability problems caused Ten-Tec to stop making this amp, but they had no other choice. I think there is a market for a solid state amp in the 600 watt class, using FETs at 50V, that isn't Made From Junk! Less than $1500 with Ten-Tec quality would make it irresistable. Hey, down there in Sevierville, how about it? A solid state version of the Centaur would be a big seller. This is a GREAT amp, if you find one on the used market, get it!

73, Denny
K3CN Rating: 5/5 Mar 23, 2004 16:12 Send this review to a friend
Super Amp!!!!!  Time owned: more than 12 months
I have owned this fine amp for 2 years now and it performs great. As I run 110v, I usually limit power out to 500 Watts to improve tube life. I find that with the sun spot cycle as it is now this is a critical addition to the shack for working in bad band conditions. The amp tunes up easily and runs flawlessly for hours at a time during contests. It is a pleasure to use and I don't have a problem with fan noise as others have experienced. With QSK and great quality in construction this one fits my needs perfectly.
W0XX Rating: 5/5 Dec 23, 2003 13:49 Send this review to a friend
Great Amp!  Time owned: 6 to 12 months
I have had my amp for some time now. At 500-600 watts output, I find I can work anything that I want as compared to my 1KW amplifier. I don't think I have ever missed a contact, 160-10.

Very cleanly layed out unit, small foot print. Fan is a bit louder, but it cools which to me is more important.

I have 811's in mine and a set of matched Taylor 572's for the day I need to replace the 811's. So far, haven't had a glitch!

WD9CMD Rating: 5/5 Nov 6, 2003 13:53 Send this review to a friend
Great Amp-Noisy Fan  Time owned: 0 to 3 months
Purchased this amp to give my Omni V a little more punch on SSB during poor band conditions. It certainly fills the bill...after...1)Replacing/slowing down a very loud fan, and 2)Replacing the 811a's with 572b's.

This rig was obviously designed for a low competitive price point when TT designed it, as such, they used low cost 811's. These tubes are not rugged enough to run 600w out. To be successfull with them, you will need to keep the drive down to 75-80w and keep output around 450-500w. It will then likely survive you. With the 572b's the rig will reach its potential and long survive its owner. Mine loafs along at 600w using 220 supply. It can do more, but I elect not to push the components past this level.

As to the fan, TT placed a very high capacity fan in the rig to keep the underdesigned 811's cooler. So, if you want to get rid of the fan noise, you should strongly thing about switching to the 572b's. The TT service is unique in todays world. That alone gives my rating a boost.

I'm now running chinese 572b's with good success. If you can pick one of these up under $500, grab it!!
VE7NI Rating: 5/5 Oct 22, 2003 09:57 Send this review to a friend
Lucky to have one!  Time owned: 0 to 3 months
I just bought one which was in great condition. I replaced the 811A tubes with 572B's and rewired for 240V operation. (I found that the pilot lights dimmed and 500W output was about all it would produce when wired for 120V; very little light dimming and easy 500W output when wired for 240V.)
The QSK operation is superb as I have an Omni 6+ transceiver to drive the Centaur amplifier. Easy to tune, looks great on the desk. The fan IS noisy but it faces away from my operating position. Lots of "room to spare" running 572B tubes and I'm looking forward to years of fine use with this amplifier!
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