[AMRadio] RE: Yet another receiver update!

[Brett Gazdzinski]

Bacon,
It drifts down.

Its not the coil warming up, as that is in a shield can, and 
does not seem to get warm.

Part of the problem may be the dropping resistors in the 
power supply.
I did not have a 150 volt transformer, and used a 260 volt one,
and drop lots in the resistors between the VR tube (vr105).

This adds more heat than is needed under the chassis.
Still, I think its mostly the oscillator tube.
It was sort of a poor choice to use octal tubes, especially
for the oscillator!

Smaller tubes likely mean lower drift.

I made some mistakes since it is my first home brew superhet...

I should have used 7 and 9 pin tubes,

I should have placed things MUCH closer together, especially
the coil, cap, osc tube and mixer.

I should have found the correct transformer before cutting
holes in the chassis.
(I originally was going to include an audio amp (pair of 6L6,s) 


Thanks for the tips,
Brett
N2DTS

> 
> Hi Brett,
> 
> Does the oscillator drift up, or down, as it warms up?  You should
> use positive or negative coefficient temperature compensating
> capacitors to reduce the drift.  Some of the comp caps can be next
> to the coil, other comp caps can be closer to the 6J5.  Nothing is
> perfect, but optimum compensation should help a great deal.
> 
> Also, you could build a frequency lock loop, using your frequency
> counter reading and a small amount of "set" memory.  When you have
> the oscillator on a desired frequency, you save the frequency
> reading in the "set" memory.  The FLL would then compare your "set"
> frequency with the readout, and apply a slow correction to the
> oscillator to keep it on frequency.  The FLL must be disabled when
> you tune; when you get where you want to be, you enter the reading
> in the "set" memory, activate the FLL, and there it stays.  That's
> how some old and very useful signal generators work.
> 
>   Bacon
> 
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