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@gmail.com>
To: <amps@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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