Hi Alek,
I don’t have any comment about #1, not sure there’s any reason to prefer
one over the other.
#2 is a little different. If I understand correctly, the reason for the cap
is to equalize the RF at both ends of the heater so that the heater isn’t
“over-lit” by the heater current plus the drive signal. I read about that
trick in Bill Orr’s book. (In the context of a 8877) I can’t prove that
it’s actually worth doing, but it will only cost you a .01 uF cap.
FWIW, I’m using the cap AND a separate bias choke in my current 8877
restoration. So far it works fine, but If I’m wrong perhaps someone can
jump in here and help us both out.
73,
Jim N7CXI
On Mon, Mar 13, 2023 at 6:36 PM Aleksandar Petkovic <vk6apk@bigpond.com>
wrote:
> I'm in the throes of building a 6m amplifier using a GS35B tube. It is
> of course, indirectly heated and has one side of the heater connected to
> the cathode internally.
>
> I have two questions, regarding various circuit techniques I have seen
> when deciding on what I'm going to use in my amp.
>
> 1. Should I use a separate cathode choke to connect the bias or should I
> just inject it at the transformer end of the heater choke, selecting the
> wire that connects to the heater/cathode junction? I have seen both
> techniques used and I'm wondering about the advantage or disadvantage of
> either method.
>
> 2. I have seen instances where there is a capacitor from the
> heater/cathode to the other side of the heater. Then, I've also seen
> instances where this capacitor is left out. Are there any reasons for or
> against using this capacitor? In my own mind, as it is indirectly
> heated, I cant see why the capacitor would be used.
>
> I would be very interested in any facts or thoughts on those questions,
> as I finalise my design.
>
> Thanks and 73, Alek VK6APK.
>
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