[Amps] Cathode Choke

[Carl]

Viewstar was a Hammond of Canada product.

B&W bought the PT-2500 and then had to redesign the tank circuit which arced 
badly. It worked well but like all things B$W it was overpriced and only a 
run of 250 was sold. As an existing B&W distributor back then I sold about 
50 of them.

The single 8877 amp was low production but Ive seen a few over the decades, 
all were Viewstar.

Carl



----- Original Message ----- 
From: "Jim" <jimw7ry at gmail.com>
To: <amps at contesting.com>
Sent: Friday, October 04, 2019 5:33 PM
Subject: Re: [Amps] Cathode Choke


> Is this a B&W or Viewstar PT3500? Is so, W8JI was not the designer.
>
>
> Thanks
> 73
> Jim W7RY
>
> On 10/3/2019 2:47 PM, Roger Parsons via Amps wrote:
>> I am attempting to repair a PT3000 amplifier for a friend. (This is a 
>> prototype of a design that never went into production.) The amp uses an 
>> 8877 in grounded grid.
>> I am puzzled about the cathode choke, as the cathode and heater are 
>> connected together for RF, all three connections go through the choke, 
>> and the heater is fed from DC. This has the undesirable effect that 
>> because of the voltage drop in the choke something over 6V is necessary 
>> to give the proper heater voltage. And the DC supply has broken and I 
>> want to replace it with a transformer....
>>
>> I can't see any advantage in doing things this way, but I may be missing 
>> something. FWIW some other amps I have worked on have kept heater and 
>> cathode separate and have worked fine (MLA2500 as original, and as 
>> modified by me to use a 3CX800, an ex CBC 1kW FM broadcast transmitter 
>> (8877), and as modified by me to be an HF Class AB1 amp.) I'm sure that 
>> other examples can be found for both techniques.
>> Is there a good reason?
>> Thanks
>> RogerVE3ZI
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>
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