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Reviews For: Ten-Tec Centaur

Category: Amplifiers: RF Power - HF & HF+6M

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Review Summary For : Ten-Tec Centaur
Reviews: 31MSRP: 749
Description:
Full QSK 600W HF linear amplifier
Product is in production
More Info: http://www.qsl.net/tentec/
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00314.8
WB2VVV Rating: 2022-07-10
Great QSK Amp!!! Time Owned: more than 12 months.
This is such a nice full QSK amp that operates all HF bands!

I bought mine from a ham that owned it a long time and had it wired for 120 VAC, and I was immediately a little perplexed that the power output seemed too low by about half, though otherwise the amp was operating very nicely and a pleasure to use full QSK with a Ten-Tec tansceiver. Its AC line cord was a little damaged and taped over as the rubber jacket was becoming brittle due to what looked like sunlight/UV damage. I replaced it with a little bit longer new AC cable suitable for an AC cord, and installed a 240 VAC plug. The line cord Strain Relief was a bit of a challenge and needed to be replaced. Inside the amp while making connections I quickly saw by comparison with the manual that the previous owner had used one of the wrong terminals to wire the amp for 120VAC. He had it wired so that the transformer had only one of its two 120 VAC primary windings in use - which explains the 1/2 power output situation as half the transformer was not even being used. Once corrected the power output became perfect! It has been a really nice amp to use with a Ten-Tec rig on QSK CW, about the smoothest I have ever used. I have used it with a Ten-Tec Jupiter and also an Omni C. I have since re-tubed the amp with 572B tubes with which it also works very well with some more grid current headroom that the original 811A tubes. Power output is about the same, with just a bit more rugged tube grids.
KZ4B Rating: 2016-02-07
Very Robust Mid-power Amp Time Owned: more than 12 months.
The Centaur Amplifier is functionally very desirable in it's output power range and physically attractive-- though relatively rare and no longer in production.

If relatively short duty cycle operation (i.e. SSB &/or CW) is the only need--then 811A Finals with 65 Watt Plate Dissipation (X 3 tubes) will suffice. There is zero power output improvement by upgrading to 572B Finals rated for 160 Watts Plate Dissipation (X 3 tubes). If more demanding/longer duty cycle (AM &/or RTTY) operation is needed then 572B's guarantee more reliable operation.

Note that only Svetlana Brand Tubes (Whether 811A,s or 572B's) have an Amplification Factor/Gain of 200--as opposed to 160 which is common with all other brands. Also, Svetlana's were engineered for the Centaur's horizontal (as opposed to vertical) tube orientation--which can be a problem with some other tube brands. The higher Amplification Factor/Gain of the Svetlana Tubes reduce the associated amplifier's relative Drive Power Requirement relative to amplifiers using all other brand tubes. This is especially important for the Centaur because it uses a less efficient "Swamping Resistor" in the Grid Circuit (as opposed to a "Tuned Circuit" used in most other amplifiers). Depending upon available Tranciever Output Power / Amplifier Drive Power (typically 100 Watts SSB/CW and 25 to 50 watts AM)--the Centaur is more likely to be Drive-Limited if using OTHER THAN Svetlana Tubes. Bottom line, try to use (OEM Ten-Tec supplied) Svetlana Tubes if possible and practical.

Note that the above-mentioned Swamping Resistor in the Centaur's Grid Circuit (while slightly increasing the Amplifier's relative Drive Requirement) helps eliminate the need for an often troublesome Neutralization Circuit and reduce Parasitic Oscillations. This inherent LACK of Feedback Oscillations/Instability (associated with Triode Amplifiers) contributes greatly to the reliability of the Centaur. Despite the improved stability, you are well advised to use about 20 or 25 feet of RG-58 Coax Cable between the Transceiver Output and Amplifier Input to further suppress VHF Range Parasitic Oscillations. This "trick" (which can be recommended for all Linear Amps) was originally recommended by Collins Radio for their 30L1 Amplifier which is a 4 tube version of the Centaur.

Many of the reviews herein mention the very troublesome Miniature "Bat-Handle" Toggle Switches which fail mechanically. They are a royal "pain" to replace--so when the first switch fails--change them all. The no-longer-available OEM Ten-Tec replacement switches are "crap". Radio Shack sells much higher quality switches : SPST (All-Metal Flat-Sided Bat Handle Mini- Toggle) 6A 120 V, 3A 240 V. Rad.Shack Stock # 275 635; DPDT (Same Specs As Above) Rad. Shack Stock # 275 636. Mouser and Newark Electronics may have something similar.

Ten-Tec no longer supports the Centaur--but maybe if/when they get back on their feet this will change.

If you get a Centaur that hasn't been modified for 10 Meter Operation--then there will be three small ferrite torroids on the small nominal 2 X 3 inch "Filter Board" located under the cover on the back of the Centaur (that accesses the 120/240 VAC Power Transformer Primary Circuit Jumper Board). If your Centaur HAS BEEN MODIFIED for 10 Meter Operation then there is only one small ferrite toroid on the SAME (same part number) board. The point is that the Ten-Tec Owner's Manual says you need a new board from Ten-Tec (which is no longer available)--but it is really the same board with two toroids removed. No other changes are thought to be needed to get on 10 Meters. Check with a licensed ham (including the writer) who has a 10 Meter capable Centaur to find out which Toroid should remain.

The Centaur's Power Transformer is very robust, so it doesn't thermally limit Plate Current, nor do the 572B Tubes whose Plates barely get red under maximum continuous loading. The Power transformer can be connected either for 120 or 240 VAC Utility Power Input--but there are no extra Buck/Boost Windings. While the Centaur is very happy being powered from 120 VAC, a 240 VAC supply is needed to maintain 1600 VDC under maximum loading. This yields 600 Watts+ PEP on SSB and a solid 500 Watts "key down". With 25 Watts Carrier Input you get 100 Watts carrier Output on AM. There is "headroom" for greater Amplifier Output with more Drive if available

The Centaur Fan is a bit noisy due to some over-kill in air flow. There are numerous ways to slow down or replace the fan as discussed elsewhere in this review. We noticed that most Fan Noise comes from the left-side Fan Inlet and not the Fan Outlet side. We built (out of 1/2" thick closed cell packing foam) a 5" X 5" X 5" Box open on two adjacent sides. One open side of the Box goes against the Fan Inlet Opening of the Centaur Enclosure and the other open side faces toward the rear of the amplifier. The noise reduction is remarkable with no decrease in cooling air flow.
VA2DV Rating: 2015-06-21
Good, solid and easy to tune Time Owned: 0 to 3 months.
This is a wonderful amp. Built like a tank,
Have all the necessary metering. Tubes are robust and inexpensivea if you need to replace them.
COnstruction and finish way better than the competition with 3 811's.
And of cource, the legendary support from TT.
Rare on the market. If you see one, grab it !
K4AAZ Rating: 2013-09-13
great amp ,rarely seen for sale Time Owned: 3 to 6 months.
Local ham had one for sale,pristine condition,he had sent it to Ten Tec for check up..I replaced 811 tubes with 572B ,replaced fan with quieter one.run 40 to 50 watts from transceiver get 400 to 500 watts out on 110 ,tunes easy,nice small amp....
N1DZ Rating: 2010-11-09
Great amp Time Owned: more than 12 months.
This is an update of a previous review. I am using this amp now for over 12 years. Modified the fan and made it nearly silent with a heavy duty serie resistor. Using 572b tubes. Recently recapped and added a Harbach soft start. Tuning is super smooth and output is 500-600 Watts. Recently I had a problem with a hanging input relais. Called Ten-Tec and within 5 days I had a replacement relais for less than $12.00. Mind you this amp has not been in production for many years. What a service!
This is a great 600 Watts amp, solidly built with great factory support. Unfortunately Ten-Tec does not make this amp anymore.
AF5U Rating: 2010-09-18
Modified - Now Almost Perfect Time Owned: more than 12 months.
I bought this amplifier as a walk-in at the factory in 2001. It was preowned. Went through several final sets of tubes both 811As and 572Bs. Blew out components on the circuit boards. One day I found and solved the problems. Also did several modifications to solve the jump off the bench when you turn it on issue (current surge), the fan (120VAC) noise (now use 24VDC fan on 12VDC), and the LOAD capacitor plate shorting. Now the thing could not be sweeter. Love the QSK in CW and ruggedness of the 811As - don't waste your money on 572Bs. Yes, you "might" get a few more watts but at what cost per watt? Need a 100 bucks in your pocket - put in 811As! The guy you QSO will never till the difference on his s-meter.
AB3EN Rating: 2010-07-16
Great used buy! Time Owned: more than 12 months.
I picked up this amp about 1 year ago. The previous owner had new 811's installed and one blew as I started it up. I replaced the 811's with 572B's and got new resistors for the plate connector board. I get a solid 700+ watts peak out of the amp with 75 watts drive, as indicated on the LP-100 wattmeter. It is a nice addition to my K3 and really helps in the morning with the rotten apples (7.238). If you can find one buy it, if run in to problems Ten Tec is there to help you. Both Ten Tec and Elecraft have the best customer service I have seen. Both make great products!
W4HT Rating: 2010-05-01
Top Quality Top Drawer Medium Power HF Amp Time Owned: more than 12 months.
I have owned the Ten Tec Centaur now for about 3 years and it been flawless. No bangs, pops, or any anomalies. It is easy to tune and still produces 500 clean watts on CW and about 600 watts PEP on SSB. By the way, I am still using the original Svetlana 811A tubes that came with the amp from the factory. I only use the it in about a thrid of my QSO's but it's great when needed. I do agree with the comment regarding the wimpy switches. I haven't had to replace any of them yet but it does not appear that diffucult to get at them. All in all a quality medium power amp with inexpensive 811A tubes, a well written owners manual, and yes Ten Tec is still in business and will answer questions reagrding this product(or anytning else they have produced over the years). If you can find a good specimen buy it and enjoy!
W8UDX Rating: 2009-12-21
A great old friend Time Owned: more than 12 months.
I was thinking tonight that every time one of my three very high-end amplifiers thumps and ceases to produce RF, I always take the cover off my Centaur, replace the big, non-functioning brute, and I am back up and running. I think that just about says it all. Thank you old friend.
WD9CMD Rating: 2008-04-18
Centaur is still perking along Time Owned: more than 12 months.
After several years on the same set of chinese 572b tubes, I must commend the TT folks for a rock solid amp. The only issue with the amp is the wimpy switches. I've replaced one last year that went bad and then..... now the Ig/FWD is bad. Bummer. Why, because they are an absolute b.... to change out. Very hard to access, and way too small for what they do. Oh well, if thats the only thing wrong, so be it. It still works like a top. Quiet with the pabst fan and excellent out put with the 572b's. Also loads up great on 17m on the 15m bandswich. I can push this amp to 800w out on 40 most any time without excess heating apparent. I'd only try this on SSB (and not for ragchew) as if you did this on another mode, excess heating may fry some components. Anything more than say 650 out is a waste anyway. If you need more go to a bigger amp !! But I find this amp to be perfectually adequate for the majority of ham operating.
Good luck, David wd9cmd

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Earlier 5-star review posted by WD9CMD on 2003-11-06

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!!