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Re: [Amps] Alpha 91b problem

To: "" <>, K9FD <>,
Subject: Re: [Amps] Alpha 91b problem
From: bmm57 <>
Date: Sun, 20 Nov 2022 12:51:04 -0600
List-post: <>
Acom does not build a transformer replacement for alpha 91b or 99, Hamilton is 
the only one who has a replacement right nowFor $1000.00 plus shipping. I have 
replaced over 20 Transformers in these 2 models in the last 6 years here at 
Array Solutions repair.Billy MacAK5DXSent via the Samsung Galaxy S9+, an AT&T 
5G Evolution capable smartphone
-------- Original message --------From: gudguyham--- via Amps 
<> Date: 11/20/22  12:26 PM  (GMT-06:00) To: K9FD 
<>, Subject: Re: [Amps] Alpha 91b 
problem I thought I heard that Acom might have replacement transformers for the 
91b/99 amps. After all Acom built them.  It’s very possible that the new Acom 
2000a transformer can be retrofitted into the 91b or they might even have 
direct replacements.  It’s worth an email to Val.  The 200a is basically an 
updated 91b it uses the same tubes so all the voltages are there in that 
transformer.  I’m pretty sure it’s $1000 but less.  Worth a look see.Sent from 
the all new AOL app for iOSOn Sunday, November 20, 2022, 11:34 AM, K9FD 
<> wrote:I have a 91B that has the exact same symptoms,  and 
it appears its the transformer.So you can add another to the list.   Also have 
a 99 and it has just went south,hoping its a shorted tube and not the tranny on 
that one.I would sure be in the market for a transformer if any one has one.  
Not sure I willspend 1000 for a new one to keep the 91 on the air.73 Merv K9FD> 
I have a defective Alpha 91 transformer in my junk pile.  WD8CCC’s amp started 
blowing primary fuses probably 8 to 10 years ago now.  The problem was an 
internal winding to winding short.  The transformer would make full AC voltage 
on the HV secondary, until the HV rectifier board was connected.  I forget now, 
it has been so long ago, which winding was shorted internally to the HV 
winding.>> I had Ben order one from Alpha.  They were kind of condescending 
about it; they did not believe it could be the problem.  Finally they sold him 
one (they had a used one), while stressing they would accept a return when it 
didn’t fix the problem.  I had the amp running already using an external HV 
winding.  Apparently at the time it was not a commonly known issue.  It was a 
new problem to me, but I only occasionally repair amps for friends so don’t see 
as many cases as folks who do this all the time.>> Sorry to hear 91B 
transformer failures are becoming more common.  Ben’s amp is still going 
strong.>> 73 Charlie N8RR>>>> Sent from 
Mail<> for Windows>> From: Alek 
Petkovic<>> Sent: Sunday, November 20, 2022 1:59 AM> 
To:<>> Subject: Re: [Amps] Alpha 
91b problem>> Yes. I have a shot transformer from a 91B here. Similar problems 
to yours.>> The owner bit the bullet several years ago and bought the Hammond> 
replacement transformer and the hv/screen supply board. The amp has been> sold 
to another friend and it is in daily use. In other words, well> worth the 
cost.>> 73, Alek, VK6APK>> On 20/11/2022 8:38 am, Terry Baxter wrote:>>>>       
 All,>>>>        Recently I wrote about a problem I had with my Alpha 91b. It 
popped>> the rear panel fuse F3 (2 amp). The problem turned out to be a bad>> 
power transformer. In my case the secondary winding for the 105V power>> across 
pins 1&2 on connector J2. This should read approx 3 ohms. My>> transformer read 
10K ohms. In addition it also read 4.5K ohms to the>> HV secondary winding pins 
1&2 on J1. A good transformer should read 3>> ohms across pins 1&2 on J2. It 
should read 10 ohms across pins 4&5 on>> J2 and less than 1 ohm across pins 6&7 
and 7&8 on J2. I measured 500>> ohms across the high voltage secondary. Do this 
quickly as it can get>> interesting if you leave the ohmmeter on the primary. 
There should be>> a wide open reading between any pin on J2 to J1. There should 
be no>> resistance between any pin on J1 or J2 to the transformer body. All>> 
resistance readings are with all primary and secondary connections>> removed 
from the Power Supply board (in other words all connectors>> related to the 
power transformer). This quick check should confirm>> whether your transformer 
is good or bad.>>>>        I had several responses asking for my findings on 
this issue. From>> what I learned a lot of the transformers in the 91b are 
failing. A new>> transformer from Hammond is currently selling for $1000 plus 
tax and>> shipping. I was fortunate to find a replacement transformer at a 
very>> affordable price.>>>>        Sorry for the length of this note. I hope 
it will help answer any>> questions on this failure.>>>>        Terry/N6CW>>>> 
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