[Amps] Alpha 91b problem

[Alek Petkovic]

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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