[AMRadio] RE: Receiver update.

[Brett Gazdzinski]

Russ,
I don't have a manual for an SP400.
I think I have everything I need as far as a diagram
goes.
I was going to call Antique electronic supply and order 
a 12sa7 when I got paid (2 weeks).
I have lots of tubes to trade....

I went home for lunch today, and tuned in 40 meters.
I found a couple of guys on...they may still be on...
The receiver sounded good, so I dug out an old B+W coil
assembly, a 3 turn link glued onto a longer piece of coil stock.
It WAS for a grid drive circuit for something, but I never used it.
Well, one side of the link to ground, one side of the big coil to
ground, the hot end of the big coil to the mixer input, the
hot end of the link to the antenna....signals jump up!
put the tuning cap across the big coil and tune it...BIG
jump in signal strength!
Its very peaky!

Listen a bit, hummmm, sounds GOOD!
How good?
I turn on the r390A and put it in the 8Kc position, then switch
back and forth between the two receivers...

Believe it or not, the homebrew sounds the same!

Conditions were very good, not much interference close to their
signals, and under these conditions, the homebrew sounds great.

I hook up the DMM to the AGC spot on the detector, and can
see the voltage moving around, so an S meter should be easy.
(circuit in Bill Orr handbook)

The tuning rate is very nice, almost like a bandspread, since
it only covers about 200 KHz.
The tuning seems very stable and nothing is touchy, although
lots of stuff is connected with alligator clips!

Next is a lot of cleanup, replacing the alligator clips,
switching out some caps for new ones I just got,
re doing the IF transformer sockets and mountings, then on to the
RF amp, S meter circuit, the buffered IF output (for scope) BFO,
muting circuit, crystal calibrator, and the front panel work.
I may get a mechanical filter from the place in electric radio
if I get the cash...
 
As it is, things have worked out so much better than I thought
possible!

I am very excited!

Brett
N2DTS


  
> 
> Hey  Brett, consider looking at  a SP400 for  circuit ideas.  
> Did you  find 
> a  12SA7?  If  not,  I  will send you  one,  email me.  Russ
>