Re: Filter problem

john larkin <jl@glen--canyon.com> wrote:

On Thu, 12 Jun 2025 17:02:59 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
 

john larkin <jl@glen--canyon.com> wrote:

[..]

>
Heck, 150 MHz is almost DC.

Not with valves, it isn't

I am avoiding the use of printed circuits, it is all being built on
tagstrips and standoff pillars - and a lot of the circuit can be
supported off the valveholder tags (but not the filters).

 
Retro look.

Not appearance but practicality.  The plan is to avoid semiconductors
altogether; with valves it is much easier to make one-offs on tagstrips
and try out different components and layouts.  At 150 Mc/s there are
unspecified hidden capacitances and inductances waiting to catch you
out.  Some valves for those frequencies were designed with a specific
layout in mind ( ECC91, QQVO 2-6,  QQVO 3-10, QQVO 3-20, QQVO 6-40).

I have known laminated printed circuit boards to track across between
the layers.   With transistors this would hardly be noticed but with the
higher voltages and much higher impedances of valves, it can cause all
sorts of strange intermittent faults.


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk