[AMRadio] RE: Receiver update.

[Brett Gazdzinski]

Hello all AM,ers.

Well, I put together a quick detector circuit last night,
a diode followed by a triode (6sn7), and hooked it up
to the marantz amp. 

The thing works!

I did not build the rf amp yet, and tried connecting the antenna
to the mixer input directly and also just putting the alligator
clip close to the input.

The receiver seems sensitive enough to pick up signals even with 
the antenna clip just close to the input to pick up
signals, with it connected directly, signals are strong!

The IF is broad as a barn door, just like a typical old tube
broadcast receiver, about 20 KHz!

I DID hear Jay, N3WWL, and others, along with about four
ssb qso,s (all at the same time) but its a start,
and I COULD copy those guys....on 80 meters, at night...
and the frequency response seemed very nice.


I still have a problem with the IF stages oscillating, and 
lots of weird actions with the IF transformers, grounding
the cases of some cause the oscillations to get worse, others
kills the sensitivity somewhat, sort of a regen IF superhetrodyne
receiver!

I also found that my mechanical filter does not seem to work.
Its old, has a big dent in the top of it, and I have no idea
where it came from...although it is 455Khz and 6 Kc.
Measuring the loss through it, it seems to have almost no
peak frequency, just a lot of loss.

These things are hard to test, not sure what load they are 
supposed to operate into...I tried various capacitors
across the input and output, etc....

Looks like I have to find better IF transformers, designed
for communications work instead of 20Khz, and/or a good 6kc
mechanical filter, and figure out why the IF is so unstable.
I suspect its the longish leads from the IF transformers and the
circuit parts....they don't fit well into the octal plug in
sockets, and I need to ground things better and maybe to one
point at each tube socket, and pay attention to the
phasing of the transformer windings.

I notice that in some handbooks, they don't use IF transformers,
but a coil and cap setup resonant at 455Khz, with capacitor 
coupling between stages.
I wonder how this works...
Coils for 455Khz can be big though...
 
The tuning rate is nice, the thing seems somewhat stable
in frequency, but then, you wont notice much drift with a 
20Khz bandwidth!


Anyone have any old junk communication receivers I can get the
IF transformers out of?

I suppose I should look for basket cases on E bay...
 
Its a real shame you cant just stop by the local radio
parts place and order anything you want like in the old days!
 

Brett
N2DTS