Howdy,


Maybe not. Imagine the top portion disconnected, it would
have very little effect. It's no more than a small capacitor
swamped out by the tuning capacitance.

I think if the grid capacitance times the square of the turns
ratio is small compared to the tuning capacitance, it can be
ignored. Because there are other strays that will require
a bit of pruning in any case.

The most significant effect would be when the tuning capacitor
is at its minimum value. So it's here that it may effect the
design of the inductor, requiring a bit less inductance for the
desired upper band limit compared to the other tuned winding.

There are no padding capacitors on that schematic. So I suspect
there are seperate tuning capacitors for each tuned winding on
the transformer. Because of this I believe it's not that
critical. You could measure the grid capacitance with the
tube mounted in its socket on the chassis. Then add that
capacitance times the turns ratio to the value of the tuning
capacitor when you calculate the necessary inductance value.

Or build the coil so you can stretch it (slip a few windings
further apart) a little once the thing is running. Then secure
them with a bit of wax.


73,
Grumpy



exray wrote in :

Grumpy The Mule wrote:


If the capacitance of the grid is negligible, then the
resonance is determined by the inductance from the
portion of the winding paralleled by the variable capacitor.

So what about the 'top' portion of the coil being effectively in series
with the tank? Wouldn't that affect the tank values?

Tnx?