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write your own review of the Alpha 91B.
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K6YE
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Rating: 5/5
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Nov 12, 2008 17:58
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AWESOME AMP
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Time owned: more than 12 months
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I purchased my 91B sometime ago. I drove it over to Alpha and dropped it off for upgrades. (It really helps to live only 9 miles from the factory). When I got it home, installed the transformer, and applied 240 volts, one of the 4CX800s shorted out. I replaced the tube and this baby now cranks out the power.
It will easily exceed maximum legal output so watch the drive power. While the directions seem complex, the actual tuning is straight forward and quite simple. Kudos to Glen and Molly at Alpha for their supreme help in identfying the bad 4CX800 via telephone. How many companies are there that still give personal attention over the telephone sans charges? In addition, they gave me tune procedures paperwork pertinent to my IC-775DSP and FT-1000D transceivers.
I am totally pleased with my amp.
Semper Fi,
Tommy - K6YE
DX IS
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N3EAQ
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Rating: 5/5
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May 11, 2007 09:59
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Just a great, solid amp!
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Time owned: 3 to 6 months
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A friend of mine had a brand NIB Alpha 91B that he had bought in the late 90's, but had never turned on, or even plugged in! He loaned it to me a few months ago to test it out, and cycle the caps and tubes.
I fell in love with it! Gobs of power with very little drive, SUPER quiet! EXTREMELY easy to tune. It has protection circuits 6 ways from Sunday, I don't think you can hurt it. "cool looking" with it's LED bar metering.
This unit was mfg. for ETO/Alpha by Acom in Bulgaria, so "really" I suspect all these positives are a good testament to Acom, and not really Alpha, but I liked his unit so much, that I just bought one for myself (used, obviously) and retired my Ten-Tec Titan 425. I really liked the Titan, but this was quieter, easier to tune, and just plainly fit into my station set-up better.
If you find one of these available, grab it, you won't be sorry!
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VR2AX
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Rating: 4/5
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Apr 23, 2006 03:14
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ETO 91B Amp OK Service Great
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Time owned: more than 12 months
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I ordered a ETO 91B from Alpha shortly after they were introduced in 1996. There were long delivery delays, the amp was at that time made by a subcontractor of Alpha in Bulgaria. Mine turned up on my doorstep about five or six months after I ordered it. I owned it until 2004 when I sold it. It was only lightly used, including two contests in late 1996 and early 1997. Many changes of qth meant and no antennas it was either packed away. I sold it in 2004.
When it worked, which it mainly did, it produced watts with an abandon that I have not witnessed in any other amp that I have owned (L4, two L4Bs, L75, 2KL plus some homebrews). In its first outing, a 160 contest, it 'cooked' a MFJ 989C that I was attempting to 'tune' a quarter wave vertical on. I had to turn the power down to about a third just to stop the inductor in the tuner from going bright orange. I bought a DL 2500 2.5 KW dummy load, original Vectronics not MFJ, to test the amp on when I had no suitable antenna. I did enjoy watching the dancing LCDs, although they overstated the actual power output significantly. Key down output into the DL measured between 1.8 and 2.2 KW measured on a Bird 43.
When it was about 4 years old, having been in storage for over 2 years, it developed a fault, low output around 50%. Suspected a tube and ordered a pair of 'new' tubes from a tube dealer in Florida. Oddly, just trying to test one of the original tubes one at a time just did not work, though I never figured out why. The replacement tubes had to be gestered for several hours, but the problem persisted.
An exchange of emails with Alpha service, in particular Glenn who was great, indicated a probable failed Schottky diode in the RF input board. I could not source the right diode here, tried a near equivalent but without any success. I bought a replacement board from Alpha, in fact it was the board for the Alpha US-made version, which was apparently identical. That worked great, full output once more.
The control board was the next thing to go, though that was my fault, not Aplpha's. Round trip shipping for the amp would have cost me $400. However as always Glen was very helpful. I pulled the control board out and shiped just that back to Alpha for repair. It did mean that I had to wait until another ETO 91B came in to them before he could test and return it to me, but that was not a problem. Everything worked fine after that, but I did decide to sell it lot long afterwards. I decided from a purely personal point of view that glass tube triode amps were more my cup of tea, though I have since also acquired a 2KL. I was also and remain a little nervous about the particular tube that the 91B and later incarnations uses.
Quality control may have improved in the later US made versions and the price has increased significantly. If I ever decided to buy another Alpha the decision would be based on my experience of how they dealt with the service issues that I experienced with my 91B.
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K9XK
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Rating: 5/5
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Mar 10, 2006 14:45
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One of the Alpha Standards
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Time owned: 0 to 3 months
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I would say that the 91B is one of the more robust, and pretty (after all, we like our stations to look good, right?) amplifiers available. I have an 87A, and have had a Drake L-7, Icom IC-PW1, and Emtron DX-2sp. Even with the auxiliary fan, the 91B is quieter than the Emtron or Icom by quite a bit. The Emtron delivers more power but is not as nice looking, and the Icom was auto-everything but put out less power. I took the middle road because I already had an Alpha 87A that was a great overall compromise.
The 91B will do 1.5kw with plenty of headroom. I have accidentally abused it by transmitting into the wrong antenna, but it didn't raise an eyebrow - it kept cranking because, well, I guess it felt that I "meant well". The 87A would have faulted right away. In some respects, that is a good quality. But in the real world, a non auto-tune amplifier like the 91B should be ready to take abuse, and it does that pretty well, it seems.
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YU1AO
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Rating: 5/5
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Mar 8, 2005 07:38
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click, just turned an alpha
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Time owned: 0 to 3 months
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Some of you may remember one of the old Alpha ads: [click] just turned an alpha ... (or something like that).
Well, eversince that ad was planted in my mind, I had an earning to have an Alpha amp. It was 30 years later when I finally got one, sitting on my shelf and waiting for the upcoming contest season.
Do not understand this joke about MSRP, since I bought mine for top dollar.
The one I have was the one I was using at my friend's shack for many times in the past. Only after several contests one of my LZ friends taught me how to tune it up to full power with ALL red leds on. Untill then, I was saving my friend's amp by tuning it up to just a single red led which is claimed to be just about 1500w, and was confirmed by Bird wattmeter. When discovered that this is trully a 2kw amp [legal limit then] it was never tuned at lower power levels eversince. Nor my friend complained, since amp worked great.
Now with the maintenance on my own expence, I might consider keeping it up to the conservative single-red-led level, and new contest rules are being helpfull to save my budget too.
Some people suggested I replace a fan that cools the xformer, but this amp was giving 2+kw for many hours in the contests in the past, and hv xformer is still young and ready for action...
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PA1HR
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Rating: 5/5
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Jul 3, 2004 01:23
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Very solid and reliable PA
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Time owned: 6 to 12 months
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I have used this linear amplifier for a while and I was very satisfied with it.
The technique and the used parts are conservative but strong and very reliable.
The look is very good; especially the LED-bars who IMHO look better then the single LED's of the later Alpha linears.
The noise of the ventilator is certainly not annoying. Same with the vacuum relays.
The GU74b tubes are reliable, easy to get and cheap.
The after sales service of Alpha Power is excellent, friendly and remarkable fast.
The review of Walt W0CP on http://www.evansplaza.com/w0cp/images/eto91b.pdf tells you more about this excellent PA.
Second hand prices is between 2000 and 2500 dollar or euro.
I can recommend this linear to everybody.
I changed it for the Acom 2000A which has about the same reliable HF unit.
Alpha and Acom linears are the best you can get.
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W8PT
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Rating: 5/5
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Jun 24, 2004 14:59
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Near Bullet-Proof
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Time owned: more than 12 months
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I have had this amp in weekly operational for over 5 years now without a hitch! used it in contests, big DX pileups (P5, TO4, etc.) running RTTY contests for hours on end and it has never failed. after this long one tube seems to be getting a bit "soft", but I still can get close to 1.5KW! I recommend Alpha Amps. 73 Rich, W8PT
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W0CP
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Rating: 5/5
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Nov 22, 2003 12:43
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Rock Solid
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Time owned: more than 12 months
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When this amp first came out, ETO provided me a sample to review for NCJ. Over the next few weeks I operated it in serval contest and its performance was very impressive. I ended up buying it! Subsequently, there have been a few engineering changes, which I've had installed, to improve reliability, and now it's become the 99. The amp is attractive, quiet, muscular, reliable, and compact. It's also easy to tune up, very forgiving, and uses a great tubes. My original review is on-line at http://www.w0cp.com
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VE3YF
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Rating: 5/5
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Oct 5, 2002 10:23
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Solid Performer
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Time owned: more than 12 months
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I purchased this used amp well over a year ago and for the same time frame have put the 91B through its paces. I have found this to be an outstanding amplifier. It's extremely stable, very well metered and has excellent protection circuitry built in. I get 1kw output with as little as 25w drive and 1.5kw+ output with about 40w of drive on all bands. I have found the metering to be fairly accurate, it matches my external Bird meters almost perfectly. The Tune and Load adjustments are bang on every time, so band changes are quick and by the numbers. The internal protection circuits are great, will throw the amp to standby for a few seconds if the reflected power or drive are too high. Have found the amp to be reasonably quiet, even with the aux fan installed. The 2 main reasons that I bought this amp was the price of the tubes, far cry cheaper than the old 8874 and 3CX800's and the quality and reliability of Alpha Power Amplifiers. Great service from Alpha, and Glenn is only an EMail away to help you out whatever the problem.
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