[Amps] RF choke selection

[Chris Tran GM3WOJ]

Hello all

I've just re-subscribed to this list, so here's a question
for everyone :-

I'm trying to modify a surplus RF deck (an auto-tune
2 - 30 MHz tube amp.) which has a 3-section plate choke.   
One section is short-circuited by a vacuum switch, and 
I guess that this was done above a certain frequency, 
or maybe over a certain range(s) of frequencies to avoid
choke self-resonances.  I've had to remove all of the
auto-tune control electronics (large parts of it were missing
anyway) but I need to figure out which bands 80 - 10m need the
extra choke inductance, and which don't.

Maybe it's as simple as e.g. below 10MHz the vacuum switch is
open, above 10MHz the vacuum switch is closed.  I've tried
measuring self-resonances using my ancient Heathkit GD1-U
GDO (that should jog a memory or two!) but I'm not convinced
by this method.   Any ideas how I can figure out the switching
in/out of this plate RF choke section ?

I have not had time to measure the inductance of each section,
but I will do this, which will help.

73
Chris     GM3WOJ
www.gm7v.com
www.qsl.net/gm3woj/amps1.htm