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[Amps] New Alpha 91b and 99 60 Hz transformers available from EPD

Subject: [Amps] New Alpha 91b and 99 60 Hz transformers available from EPD
From: Kimo Chun <>
Date: Mon, 14 Mar 2016 14:36:30 -1000
List-post: <">>
​I finally got around to testing, albeit briefly, the new transformer I
asked and  Electronic Product Designs (EPD, Inc.) to prototype for me. At
our contest station we have 2 Alpha 91b amps with the presumed
Bulgarian-made transformers. Eventually, both transformers failed. Under
load they short out. The 99's have Peter Dahl-made units and haven't failed.

As we had time (we have spare amps) I decided to find out if a replacement
transformer could be added to either Hammond or another vendor's line. I
decided to work with Peter Eggimann, the owner/designer at EPD.  I made
measurements of the tight space in the amp and eventually sent him one of
the bad transformers as a sample to ensure success. It took a year or
more but he made a small batch of final products late last year.

I believe he questioned whether the core of the original was adequate and,
for now, came up with a 60 Hz version that fits. I understand a 50 Hz
version would require a different core and may not be
determined. He designed conservatively, thus the dilemma.

Another ham in the southeast  (FL or GA) also inquired later so he worked
with him on a prototype as his amp was close by for possible shipment back
and forth, during development, if needed.

As our second 91b amp collected the bad parts I didn't install the
transformer upon receipt. I decided, during the recent ARRL DX SSB (as some
ops weren't operating) to just put the new transformer into the working 91b
to test. After a few minutes warm up we keyed down at 1500W into our 40m
yagi (during mid-day) for several one minute tests (with ID). No problems.
We'll be further testing the amp with the transformer in one of our
upcoming Multi-Multi efforts.

I am confident it will work well. It is plug and play compatible though you
may end up using larger SAE screws/bolts rather than possibly
smaller diameter metric or smaller SAE originals (I didn't bother to
check). The holes in the amp are large enough and they thread into nuts or
threaded tabs on the transformer base. The hardest thing is to remove the
main 240VAC multi-pin plug. You need good finger power or a screwdriver
under one of the new connector ear locks to get them to both clear the
locking nubs on the mating jack. Hey, it's new. It was well packed and
shipped (typically) bolted to a wooden base and surrounded by a heavy
cardboard-with packing cover.

It is rated for 3.462 KVA, 1PH 60 Hz.  Primary: 120/240V (100V taps)
Secondary: 2050V @ 1.5A, 105V @0.5A, 310V @ 0.5A, 28VCT@ 3.0A, 13.3V@ 7.2A

It weighs approx. 48 lbs. Shipping weight: 60 lbs.

List Price: $630.00.  All of the above is subject to change as my original
quotes were based on some early assumptions (like selection of core subject
to testing). I believe he went with a larger core than quoted. You can
imagine adding shipping to KH6....

You should contact EPD if you are interested and get a quote.  I have no
connection with them other than being a satisfied customer and being glad
they were easy to work with in developing this for the ham market. You may
see their ads at times in the  CQ and/or QST magazines.

See you on the air.

Kimo Chun, KH7U
Chief repairman at the KH6YY contest station, currently using the KARC club
call KH6J.
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