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Reviews For: Alpha 91B

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

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Review Summary For : Alpha 91B
Reviews: 52MSRP: 2798.00
Description:
Replaced by the ALPHA 99.
Product is not in production
More Info: https://www.alpharfsystems.com/
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00524.9
W8PT Rating: 2004-06-24
Near Bullet-Proof Time Owned: more than 12 months.
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
VE3YF Rating: 2002-10-05
Solid Performer Time Owned: more than 12 months.
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.
AD3G Rating: 2002-08-11
NICE AMP Time Owned: more than 12 months.
Tough to beat...great construction,inexpensive tubes. Bought mine used and run the pants off of it,and it doesn't seem to mind. The LED meters took a bit of getting used to,but after a using amp for a while,I think I tend to prefer LED meters instead of analogue ones.Unintentionally tested the auto-protect (wrong band switch position)works as it should.Nice and quiet. Great amp on the used market,considering the price of a new Alpha 99.
KW9D Rating: 2002-07-16
Fine equipment Time Owned: more than 12 months.
I got mine used directly from Alpha. Its the first big linear I've ever owned. It has worked flawlessly. I use it mostly on Navy MARS working way out of the amateur bands. As low as 3.2 Mhz and as high as 4.8 Mhz in the 80 meter band position. At these extreams it tunes up fine but the loading is less than ideal. It will put out 1500 watts with ease, inspite of being this far off design. It works QSK perfectly. I have used it on Pactor a few times when propagation was terrrible and it was flawless. I have tested the protection system accidently a few times when trying to transmit when tuned on the wrong band - its always done its job.
I really like the led meters - they give peak power indications without guesswork. Blower noise is modest. About the same as my old Gateway computer. I do have the extra cooling fan, factory reccomended and installed. There are two things that I wish Alpha would have included in the original design : The ability to monitor and adjust tube filement voltage, plus a low level RF sample port for monitoring RF waveshape on an oscilliscope.
This amp is very heavy when the power transformer is installed. It needs tobe very close to its final resting place before that assembly is made. Its nearly impossible for one guy, even a real big guy, to move it by himself.
The only one complaint I have is that the QSK vacuum relay is quite noisy when working CW. Even with headphones on it makes quite a clatter. It would be real distracting without headphones.
K0ZN Rating: 2002-02-27
Solid and reliable amplifier Time Owned: more than 12 months.
PRO's:
I have had the 91B for two years and have had no problems with the unit. It just sits there and "does it's thing" without complaining. The protective systems are worth their weight in gold; sooner or later everyone makes a mistake on settings or antennas. The protective systems DO work. I typically operate mostly CW at well under legal limit and the 91B is quite happy: I say this because some amps don't like to be operated well below normal full ratings: they can get hot or get non-linear. In a call to Alpha I was fascinated to find that the "tune" LED scale is really a gain scale, and was advised to operate at lower levels with the "tune" LED somewhat to the right of the normal tune mark, thus allowing more drive power to be used. I was told this actually reduces plate disapation heat a little. However this is not critical. I drive the 91B with a TS-570 and had some initial nightmare problems with the 570 putting out a very short, but full power 100 watt spike, which instantly drove the 91B into overdrive protection shut down.
Kenwood engineering eventually solved the problem, but the message is be sure your exciter is clean, operating properly and puts out the amount of drive you think it does!...because the 91B has a LOT of gain and will instantly react to improper drive. It took me a little while to get used the LED's instead of meters, but now I love them. The construction inside is high quality. Alpha's customer support seems to be very good if you have questions.

CON's:
There is some noticeable air flow noise from the tube cooling exhausts, but it is acceptable. I get the impression that if you are a serious contester, especially on CW or use continuous carrier modes, you truly do need the additional cooling fan kit. If/when you pull the tubes out of the sockets to clean & remove dust, be very careful to get the grounding ring back on correctly! This is a little treacherous, so pay attention to make sure the ground ring is reinstalled correctly. The several minute wait period for the cathodes to warm up requires a little "planning ahead", but I really haven't found it to be a problem.

Bottomline: Alpha 91B's are not inexpensive, but you get a reliable, top-of-the-line design, high quality components and good factory back up, which constitutes high value "package" for the money spent. I am still very happy with my decision to get the 91B.
K8ND Rating: 2001-05-04
Solid Cost-Effective Full-Power Performer Time Owned: more than 12 months.
I bought the Alpha 91b new in 1997, and have used it in many contests and pileups since. It puts out the legal limit all weekend, and keeps me from sitting for long periods in a pileup on a new one during the week. Mine has just returned from a repair: after 4 years one of the 4CX800A tubes developed an internal short, resulting in reduced output (!) and on-the-air reports of audio sounding like a UA9 coming over the pole. The tubes have a one-year warrenty, so it was not covered, although the overall amplifier is still covered by warrenty. Total cost, including a new 4CX800A, upgrades, and shipping back from Colorado? $135! That's a cost-effective amplifier! I've just purchased a second Alpha 91b to use for SO2R contesting.
OK1KT Rating: 2000-08-18
Excellent PA Time Owned: more than 12 months.
As a member of the DXPedition crew in Pacific 1998 organized by OKDXFoundation I´ve had a chance to operate Alpha 91b more then 7 weeks under very hard weather conditions when temps inside rised more than 35 degrees Celsius, mostly 24 hrs a day.
The amplifier alive even very brutal handling of different airports staff which confirming the very good and sturdy construction. I was so excited of the amplifier features that I bought it for my shack immediately we returned from the DXPedition. After two years of daily use I can very warmly recommend the ALPHA linears as very good constructed and done rig.
PA1KW Rating: 2000-07-15
the best Time Owned: 3 to 6 months.
I bought this A91B secondhand 1 year old.
Before i was using a TL922 wich is also a very good amp, without problems.
But now i am used to the 91B i dont want to go back in the past, because it is a very nice silent linear wich give me 1500 watts with 60 watts drive, and you think you are running without an amp, because you dont hear it.
I had some questions to Alpha power in the US, so i mailed them, and the same day i receive a good answer, wich gives me an very proffesional impression of this companie.
Easy tunning, cheap tubes, and a nice design.

Alpha congrats.

Bert PA1KW
K9TM Rating: 1999-10-26
Kudos to Alpha, Time will tell Time Owned: unknown months.
I have a 91b which was one of the first ones out the door. I am the second owner of it (original owner purchased an 87A). From the start I had problems with the amp. The amp just spent a week in CO and when it came back, the problems were still there. Turns out that one of the problems and a major one was the transformer (which typically does not get returned with the amp for repair).

That is the bad stuff (if you want to view it that way). The good stuff is that John and the rest of the Alpha staff treated me very well and worked with me through the problems. We ultimately ended up with the amp now working as it should :-)! I intend to hammer it this weekend in CQ WW and see what comes of it. I expect that it will be rock solid.

Bottom line is that Alpha stood behind the amp and worked to solve the problems. They were more than fair with me and I have no reason to think they do business any other way.

I am looking forward to years of happy service from my 91b.
NA4M Rating: 1999-10-11
Fine amp Time Owned: unknown months.
Purchased my 91B new in Nov 1996. The amp tunes smoothly and loafs at 1.5 KW out. I installed the new external auxiliary cooling fan and it is much quieter than the original fan.
The internal cooling fan for the tubes had a problem after some period of time. It was replaced by Alpha and has worked fine ever since. The 91b is a rugged amp that should serve well for years to come.