Re: Help with tubecoil
This post makes me very curious:
> Original Poster: "Dr. Resonance" <Dr.Resonance-at-next-wave-dot-net>
> No on the 4.5:1 for vacuum tube coils. This is a resonance transformer mode
> so height ratio should be around 10:1 to 14:1 for best results. Also, use
> very small wire like 40 or 42 AWG polythermalize. In this mode voltage
> buildup is more standing waves and transmission line effects than
> transformer action.
Can you explain why this should be better given that the Q of a long
coil wound with very small wire is low and voltage buildup on a CW
coil is heavily dependent on the ability of the driving oscillator to
supply the losses inherent in a low Q resonator? I realize that once a
discharge is initiated, things change with regard to where the most
dissipation occurs but standing waves are also largely transformed
into travelling ones. Does initial voltage buildup not matter that much?
> For best impedance match you need a lot of turns on primary. I would
> suggest starting with some 14 AWG and around 40 turns. Tap it down as
> necessary until you get the best resonance. Run a variac to control only
> the plate voltage on the tubes during testing (not the filament of course).
> Be sure to use a meter in the grid circuit as you are adjusting your drive
> on the tubes and also a plate voltage meter to see what potential you are
> applying. These are only necessary during initial testing. Don't exceed
> the recommended grid drive to the tubes.
> Coeff. of coupling must be very tight on tube coils for best performance.
> Use parasitic chokes on both plates of each tube and also parasitic chokes
> in the filament supply (See older version of ARRL Radio Amateur's Handbook
> for help on this subject -- around 1970).
What are the experiences of the various tube coilers on the list?