[Amps] Alpha 91b problem

[Jim W7RY]

Remember that Heybour transformers does great work too.

I've had great luck from their HV transformers.

73
Jim W7RY


On 11/20/2022 12:42 AM, Alek Petkovic wrote:
> 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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-- 
Thanks and 73, Jim W7RY