Thanks Jim.
To me, that explanation sounds plausible, so I'll probably include the
capacitor.
Likewise, in the YC156 amp I built, I have a separate cathode choke, so
today I wound one on some 1/4" fibreglass rod for the impending 6m amp.
Cheers, Alek VK6APK
On 14/03/2023 12:12 pm, Jim Barber wrote:
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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