[Amps] Cathode Z GS35b

[Peter Voelpel]

This one is S= 25-40 mA/V according to the original data sheet.
Driving impedance therefore is 25-40 ohms in GG

73
Peter


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of David Craig
Sent: Montag, 26. Januar 2009 19:52
To: amps at contesting.com
Subject: [Amps] Cathode Z GS35b

    Anyone have a fairly accurate figure on this?  I read everything I can
find- have found everything from 20 ohms to 110 ohms.  The Russian tube spec
sheets don't contain this information.  
    The one solid value I found on a particular webpage (90 ohms as I
recall) wasn't accurate, at least for the tube I am using.  In that case I
designed my own tunable Pi input (6m monoband).  It tuned perfectly (roughly
half-meshed each cap) using a resister/capacitor to ground in parallel to
simulate the cathode Z of 90 ohms, in situ it doesn't use near as much
capacitance as I expected, though it does work like fine & is fairly broad.
I am not sure how much drive the circuit is losing as a result however.
    Asking because I built another one previously using the "T" input that
seems popular (yes, I have read that the "T" is really a "pi" when one takes
into account the tube capacitance).  The circuit is generally ~4000pf silver
mica in series from the RF in relay to a 10 turn 5/8" coil, variable
~20-120pf cap to ground and another 10 turn 5/8" coil to the cathode (fed in
my case thru a .01 RF rated ceramic cap in series for blocking).  Maybe I
haven't found the "magic touch" with the T- this circuit seems extremely hi
Q, I am having a devil of a time now getting the first amp input tune to go
below 2 to 1.  Best I could get in the past was 1.7 to 1.... had a problem
with the fixed bias, repaired it, and now for whatever reason can't get the
tuned input circuit under 2 to 1.  Squeezed, expanded, removed turns... Am
about ready to forget using the T as the tuned input unless I can find the
right cathode Z to simulate.  It is a PITA to repeatedly tweek the coils &
completely as  semble & test the circuit in situ.  73 Dave N3DB
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