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Re: Tube TC plate/grid coils

Hello,


At 10:36 AM 10/3/1999 , you wrote:
>Original Poster: Grayson B Dietrich <electrofire-at-juno-dot-com> 
>
>Hello, all
>
>I've been thinking, and have a few questions. 

"Thinking", Now that IS dangerous!

>
>For adjusting the tank circuit in a tube TC, varying the inductance of
>the plate coil is one way to accomplish this, right? I know that changing
>the capacitance is the usual way to go, but what if the plate coil were
>split into two sections, the distance between which being adjustable? The
>inductance  could then be easily adjusted through changes in the mutual
>inductance, right?

Now that is an interesting idea. I have usually used a combination of
adjusting tank C and adjusted tank L via taps in the primary coil for
tuning. One problem (or maybe not a problem), is that it will change your
pri/sec coupling (but then, so does tapping the primary).

>
>I've heard that it is best to keep the same number of turns in both the
>plate and grid coils, so perhaps two sections of grid coil could be used
>as well, perhaps have twp pairs of coils, where the top set of a grid and
>plate coil would be fixed demensionally to each other, and the same with
>the bottom set, so the inductance would remain the same (?)

I'm not so sure the grid and tank coil need this relationship. Often they
may have close to the same number of turns but inductance is not very
close, due to different wire size, etc. Perhaps you are making it a bit
more complex than necessary?

>
>Also, would allowing the distance between the grid coil and the plate
>coil to be adjustable have an effect similar to adjusting the grid-leak
>resistor/network?

Not really, but it is useful, as having a adjustable grid coil, is very
helpful. Tube coils are very finicky, and need lots of fine tuning, so
being able to adjust the grid feedback is very necessary.

Regards,

David Trimmell

>
>thanks,
>
>Grayson Dietrich
>www.electrophile.8m-dot-com
>
>
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