[R-390] R-390 AProduct Detector

[Mark Huss]

There are several available, depending on how much modification you want 
to do. The limitation of the R-390 and R-390A for high-quality SSB 
reception are in two areas. First is that the BFO injection level is too 
low. The second is that the AGC is not optimized for SSB. Paul Lee was 
probably the first to address this. It involves adding a switch, 
replacing a tube, and some extensive wiring.

The second, and probably most popular is the ‘Lankford’ mod. Developed 
incrementally by several people, it does not involve extensive 
re-wiring, and addresses both the BFO Injection issue and the AGC issue.

A third one is a little black-box unit that a few R-390A's were fitted 
with. The wiring is unknown to me (anybody out there know?), but it 
fitted behind the front panel, and provided fixed BFO and, possibility a 
detector and AGC.

A forth one is to add a separate SSB detector/BFO at the IF Out. Several 
Mil-Surplus detectors do this, as well as the Hammarlund HC-10. The 
latter has the advantage of providing notch filters and bandwidth 
filters, though it is expensive at about $300.

The latter option just got a lot cheaper if you have access to a 
reasonably fast PC. A lot of Hams are playing with a little device 
called a SoftRock. What this is is a IQ mixer/Detector that feeds a 
wideband (96 kHz) signal to your sound card. Designed originally as a 
direct conversion receiver for the HAM bands, several have experimented 
with it as an IF detector. At about $20 per kit (and there is one 
designed for 455 kHz), you can connect it to either the IF Input, or the 
back panel IF Output through an attenuator. The result is a detector 
that with the help of your PC will do AM, CW, USB, LSB, ISB, FM, and 
about a thousand filter combinations, including notching. Add a diode 
and buffer circuit, and you can generate AVC to feed the R-390.

I have documentation for all the above.

Keith Densmore wrote:
> Hello All,
> Now that I have the PTO aligned and stable its time for the next round. Does anyone know of a 'known to work' schematic for an R-390A product detector? Either something solid state, something that uses a 6BE6 or one that uses the ballast tube socket would all be interesting to consider.
> Thanks All, 73,
> Keith, ve3ts
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