[AMRadio] re: R 390A

[Brett Gazdzinski]

Ken,
It was a really fun project.
I did it last winter.
It was one more step in the completely home brew station,
and the original idea was just something that I could use
under good conditions, sort of one step above a regen.
But after fooling around with the design some, it actually wound
up working better than anything else I have, so now its the main
receiver.
I am starting design number 2...
 
I wanted:
Super heterodyne,
455 KHz IF,
Single conversion,
octal tube types,
80 and 40 meter coverage,
Hi fi audio.

I started with the schematic for my Scott SLRM, since its
455 KHz and single conversion, and uses octal tubes.

I quickly ran into trouble with the rf amp and coil setup,
as well as the local oscillator layout.
 
I found I did not need the rf amp, and just used two tuned
circuits before the mixer.
I started out using plug in coils for the local oscillator, but
got very tired of going around back of the rack and changing them,
so changed it to band switched and added 160 meters.
I added an S meter circuit out of the handbook, a low distortion
detector off some web page, played around with the agc and manual
gain circuits, then added a digital frequency readout as I was so bad
at marking scales on the various dials I have.
I got it as a kit from almost all digital electronics, its
backlit and very cool looking, and accurate.

For a filter, I used a kiwa thing, 5.5 Kc wide.
Its a small thing, has an op amp input, 3 ceramic filters of slightly
different frequencies, and an op amp output, runs off 5 to 20 volts
dc and has no loss, and it works great!

A muting circuit (relay), a scope output (IF),a nice paint job
on the front panel with lettering for the controls, and its done.

The tuning rate and range can be picked when building, as well
as the ability to have the same dial setting read 1880, 3880, and 7290
as I switch between 160, 80 and 40 meters...

Then I found I needed a bfo to zero beat the AM qso,s, so I built
a 455 KHz crystal oscillator with a variable output level
adjustment. 

I now want to build another receiver using 7 and 9 pin tubes, and have
started on the design...

The big help in building the receiver was having a spectrum analyzer
from work to use with setting up the local oscillator, mixer and IF
stages...very handy to measure frequency and amplitude of stages.

Its really not that hard to build a nice receiver, the hard
parts to find were the tube type IF transformers, and I found a bunch.

I just got a shock though, the coil stock (B+W) is $50.00
each, even for the little coils like the 3012 and 3016! 

Brett
N2DTS


> 
> Brett,
> This is the first I've heard about your simple
> superhet. Is ther more info that you'd be willing to
> fill me (us) in about it? I need a project for this
> summer. I have been considering a Regenerative tube
> receiver, the superhet would be better of
> course.Thanks in advance.
> Ken KC8QO
>