[Premium-Rx] RE: Drake R7 sensitivity upgrade

[Carcia, Frank A. HS]

    Hi Dan,
I rebuilt my TR7 last year and wish I changed the diodes. It does have some
weak
signal problems. I remounted the VFO by drilling the inner heavy panel and
installing
flat head screws in from the front. This is behind the front panel with all
the nomenclature printing .
 I also tightened the Allen screw loading the VFO shaft to make it stable
again.
   The tuning feels much better than stock.
I used DEOXIT on all the connector pins for each board.
QEX some years ago did an extensive article on TR7 modifications. You might
want to get the CD. I once measured the dynamic range of the TR7 RX and it
is pretty good 95 dB. The weak signal thing always bugged me when I work
Japan on 75 meters.
I don't like pass band tuning because it is a band aide for good filters. My
hot rod RA6830 has cascade filter modules which works very well. I bet a
RA6830 filter module could be stuffed in the back of a RA6790. TR7 is a nice
old rig without uP noise.
 
fc      

-----Original Message-----
From: Dan Neves [mailto:NDan at heinze-institute.com]
Sent: Monday, March 10, 2003 2:41 PM
To: Premium-Rx (E-mail)
Subject: [Premium-Rx] RE: Drake R7 sensitivity upgrade


 

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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