[AMRadio] RE: receiver info needed...

[Brett Gazdzinski]

Hello all Am,ers!
I am planning some sort of simple AM receiver for AM reception.
My requirements/specs are....

Plug in coils ok.
80 and 40 meter operation only.
Can tune a small range of the 80 and 40 meter band (AM windows).
Will have push pull (Williamson ckt) audio output.
Rack mount construction.
Want to use a mechanical filter (4 or 6 kHz).

Parts I have on hand...

Pto assembly out of a t368..outputs 1.5 to 3 mhz,
Nice National dial for main tuning,
All sorts of chassis sizes,
Vernier knobs of various sizes,
Rack mount front panels of various sizes,
A big cabinet with a door in the top (dx100 style) if needed.
Power and audio output transformers, chokes, caps, etc.
Lots of 262 and 455 kHz IF transformers.
Many larger ceramic coil forms, plugs, etc.
Lots of small tubes to pick from.
Diagram of low distortion AM detector (tube type).
Many nice small variable caps and trimmers.
 

Parts I can get...
Anything from fair radio or antique electronic supply,
including a pto 455khz bfo (fair radio, $17)
(for zero beating the receiver)

My questions are:
The t368 pto puts out 1.5 to 3 mhz with lots of harmonics,
can I use that as the local osc to convert the received frequency
to 455 kHz by using it with tuned circuits that resonate at the correct
harmonic frequency?

Would it be better to build a regular lc oscillator, changing
the frequency to change bands?

Since there seems to be no schematics for what I want to do,
and what parts I can get, it seems I will have to take chunks
of schematics and stick them together....

Audio output circuit,
Detector circuit,
AGC circuit,
Mechanical filter in/out,
IF stage design,
RF pre selector,
BFO (if I use 455khz, I got that covered)
S meter amp (got to have one).

The tricky part seems to be the local oscillator and mixer bits,
with the image rejection and noise concerns (maybe reduced by the narrow
frequency range of the receiver).

Anyone know and problems with single conversion from 3.8 and 7.3 mhz
to 455khz IF frequencies?

I do not expect it to out perform my R390a, just be usable
for some AM reception when conditions are good, so I can
make another step to a complete home brew station...

If I don't come up with a big project, I tend to play with the stuff
that is working fine, sometimes with bad results!

Last one was changing the power supply for the pair of 813,s
from variac input to switched primary taps on the power transformer
to select the output voltage...using 3 relays and a front panel switch.
This was to eliminate the 60 hz buzz....
I got the wrong voltages out, and the buzz was still there!
(its the choke I guess, not the variac or power transformer)
The end result was 2 'extra' holes in the chassis!

A receiver should keep me busy all winter and away from the working
stuff!

Thanks for any tips,
Brett
N2DTS