[AMRadio] RE: Receiver update.

[Brett Gazdzinski]

Well, thanks Mike, that's very nice of you.
Glad I ran into you on 40 today, are there any parts you
are looking for?


The receiver is really rolling along, with the detector and AGC
circuits all wired in, not with alligator clips like it was.
The IF is stable, the mixer works well, I made up the antenna
input circuit, and adjusted the coil so the RF tuning covers
both 80 and 40 meters without changing the coil.
I made the coil on a ceramic coil form like what's used
for grid input circuits on big amps, 1 inch diameter,
with groves for the turns and holes to pass the wire through.
A 3 turn link does the antenna, the big coil has a vari
cap across it.
As it is, the receiver is very useable if conditions are not bad,
but if there is a strong signal just a few Kc away, it takes
a beating.
The fidelity is very good, I took care of the overloading
on strong signals I think.

I started work on the RF amp...I had no luck with the
first design tried (the Scott) as it takes special transformers.

Bill Orr to the rescue, found a different design that uses
an RF choke in the plate circuit of the RF amp, a coupling cap
to a coil and cap resonant circuit that feeds the mixer input.
I have found the mixer input needs to see a low resistance input
or its unstable (or too sensitive).

I can make up a coil on a slug tuned form so it resonates
at the same spot as the RF input circuit, since the caps are ganged.
So, basically the RF amp has a tuned input and output.

Building the receiver is really fascinating, and I have been
spending a lot of time on it, even while on the air...
And I use the receiver to listen to something while I am
working on it, and all during my operating today.

My thanks to all the list members who offered parts and old 
receivers.
I don't think I need anything, I got the IF stages taken care of,
it was just a matter paying attention to details like grounding
and phasing.

I still need some sort of filter, my thanks to Gary for
the info on the Kiwa filters, I will have to look at their info.

I don't think I want a crystal filter, they seem to have a 
peaky response unless you use a lot of slightly different
frequency crystals.

Well, back to the RF amp.....
 

 Brett
N2DTS

> 
> 
> Hey Russ, I beat you this time. I already mailed a 12SA7 out to Brett
> earlier today.
> Oops, Brett may have found one I don't know I just figured I 
> would mail him
> one.
> 
> Brett, you got a tube coming................73, Mike / WN3B