[Hammarlund] SP-600 double conversion question

[James A. (Andy) Moorer]

Much sympathy for the re-recapping job. That's a lot of work.

----- Original Message ----- 
>
> The bands from 7.4 MHz and up (the double conversion bands) are a bit 
> weaker than the single conversion ranges -- by about 6-10 dB. My own 
> receiver shows a fall-off, too, but not quite as much.  Can this be 
> normal?

All SP-600s do this. The DF models do so a bit less than the others. 6-10 dB 
is not out of line at all for some receivers.

>
> And one other thing...  In aligning both sets, I have to crank the slug of 
> L31 all the way in to get a peak reading during the 3955 KHz IF tweaking. 
> I tore open the transformer pod on both receivers and replaced the mica 
> caps tied to the coils, but no difference was noted.  Any ideas?  Maybe my 
> alignment procedure is incorrect. I'm going by the book (Issue 4)
>
This doesn't sound right. The only time I have seen this is when the mica 
caps have been open. It means that the coil is not resonating. I use Issue-4 
for alignment, and I have never (in 15 different SP-600s) seen this happen 
that couldn't be fixed by replacing the mica cap. I guess I would try some 
different values from the stock 85 pf and see if you can get a resonance.

The other thing I have seen is when the other end of the twisted-pair that 
leaves T1 and goes down into the IF stages does something bad at the other 
end - like has one wire not connected. The receiver will actually continue 
to work quite will with one side of the TP disconnected, it will just be 
weak on those bands.

Hope this helps.

James A. (Andy) Moorer
www.jamminpower.com