[Premium-Rx] RE: Drake R7 sensitivity upgrade

[Dan Neves]

Hello everyone:
 
This weekend was surgery weekend for the R7. The 6790GM has been showing
up the Drake lately. In searching the Internet, a suggestion was found
by Pete Gianakoupolos in hardcoredx.com, that these Drake R7 and TR-7's
could be modified to increase sensitivity and lower the noise floor.
 
The 1N4148 diodes in the translator board and 2nd Mixer were replaced
with 1N5711 Schottky diodes. This apparently improves MDS from the R7's
.15 to .07 uV, an already superb figure. Please bear in mind I do not
have the equipment necessary to bear this out for fact. I do, however
have a soldering iron...
 
The results were apparent in the nightly showdown with the 6790GM. The
Drake showed a significant improvement in weak signal performance and
seems easier to listen to, as the noise floor has definitely dropped to
a new low. These 2 receivers are again most definitely on par in my
humble experience.
 
Listening for weak DX with the Drake was made with optional 4Khz filter
in "synchrophase" sideband mode. It is said this allows about 3 Khz of
bandwidth thru, while with the 6790GM the 3.2Khz SSB filter is engaged
for synchrophase detection use. Very much the same performance,
startlingly so..
 
Having a little success of course is addictive...and now the questions
turn to the group experience. The audio train probably does not have the
very best capacitors available as fancy types were out of reach back
then. Also electrolytic capacitors in the voltage regulation area may
not impart the best quality to audio.
 
The audio on the 6790GM of course is positively symphonic, and my half
deaf 93 yr. old mother in law can listen to Radio DW in the evenings in
German as though the announcer is standing next to her yelling in high
German directly into her good ear...  ; )
 
If only the 6790GM had the IF notch and PBT (knob) of the R7 and the R7
had the stability, and ease of tuning of the 6790GM...
It is interesting to note that for around $550.00 a cure is available
for these maladies in the form of the SE-3 for the 6790GM and the RV-75
VFO for the R7. 
 
Does anyone in the group have any suggestions for further mods as it
seems the R7 here has just had its claws sharpened to good effect...
 
I will have some of these hot carrier diodes left over, as the mod took
8 .If anyone is feeling adventurous just let me know off list and I will
send em over for free...
 
Cordially, Dan Seven
 
R7 6790GM 6217E  

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