[Amps] Triode Questions

[Aleksandar Petkovic]

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 at 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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