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Re: Help with tubecoil



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.

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).

Regards,

Dr. Resonance




-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Sunday, February 06, 2000 3:58 PM
Subject: Help with tubecoil


>Original Poster: "Tero Ranta" <dixie-at-netti.fi>
>
>
>Dear List,
>
>I have just acquired two QB3.5/750 transmitting tetrodes. American
>equivalents are for example 4-250A and 6156.
>
>I'm planning to use them probably in push-pull mode.
>
>Some class-C operating info:
>Ua:     4000V
>Ia:     312mA
>Pa:     248W
>Pout:   1000W
>(ug1g2:  5.1)
>
>What kind of a primary/secondary coil would best suite these tubes? I have
>bad experience with candlestick secondaries. Would the Dr.Resonance
>suggested 4.5:1 ratio be the best?
>
>I'd also like to hear suggestions about what kind of parasitic/RFI
>suppression to use with such a coil.
>
>Please send your replies also to tero.ranta-at-bigfoot-dot-com
>
>Tero
>
>
>