b33. Drake R-4C Mods


Reference pages:
b31 type 1-A, 2-A, 2-B
b32 type TR-4, TR-4C




Improving R-4C third mixer (temporary text, because the first is lost).
R-4C (S/N 22000-up).

Got this receiver at very low price because a friend didn't want to have it as it was some bad noise. We traced
it to the third mixer. It seems that 6EJ7 wasn't as good as the previous 6HS6 for this type of mixer. LA7MI
discovered that a Philips EF184/6EJ7 didn't have the same amount of white noise problem, but still it was
some desire to have it improved. This was described in '73' (June 79) by W5DA Howard J. Sartori, and solved
that sort of problem. The first direct fault was that the wire from the IF coil were broken close to the solder
lug on the IF can, LA6VM Erling had the problem on his R-4C first, so I could just follow his instructions.


How to build a proper mixer with a pentode is old news. Below is shown how it was already implemented
in 1936 for the German 80m CW/AM transceiver Torn.Fu.b1:



How to design proper mixer with a triode or a pentode may have been forgotten,
but the principle was already known in the thirties, you could of course use cathode injection,
but the conversion gain is very low, somewhat more complicated with directly heated valves...


R-4C VFO leakage into the 1st IF

It was found impossible to use SB-620 Scanalyzer with R-4C, and I was curious to find the reason.
Connected a high impedance probe (Mosfet buffer) to the input of the first xtal filter and selective
voltmeter (Siemens D2008) to measure the levels.
I'll have to recalculate the figures later. -30dB = 50mV, here is the preliminary list as found from some old paper
I wrote in december 82. Apart from the fact that R-4C has 6EJ7/EF184 and the predessors have 6HS6 as first
mixer it is likely that it is not so much difference between Drake R-4 and R-4C (S/N 22000-up).

RX frequency VFO kHz (4955-5455) VFO Level at IF IF level for CALIBRATOR
28.0Mc/s
28.1
28.2
5455
5355
5255
-30dB
-34
-36
-66dB ( =S9+10)
as above
as above
28.3
28.4
28.5
5155
5055
4955
-38.5
-41
-43
-66dB ( =S9+10)
as above
as above
21.0 5455 -38 -68dB ( =S9+ )
14.0
14.1
5455
5355
-41
-47
-67dB ( =S9 + 10)
as above
14.2
14.3
5255
5155
-49
-52
as above
as above
14.4
14.5
5055
4955
-54
-56dB
as above
as above
7.0 5455 -52 -69dB (= S9)
3.5 5455 -54 -62dB (= S9+20)
1.5Mc/s 5455 -45 -66dB (= S9+20)

*) RX pre-selector is tuned for maximum deflection for the calibrator signal.

With receiver tuned to 14.0MHz, with/without calibrator on, the IF level for S9 deflection is -95dB (5642kHz).
For AM a spurious is measured at 5595kHz at -81dB level (xtal oscillator)
For SSB a spurious occurs at 5645 at -95dB (xtal oscillator)

With VFO level at 30-35dB above the strongest signal on the band it should be proved that it is quite difficult
to use a scanalyzer (SB-620) connected to an output from 1st mixer.


The following measurement of AGC voltage vs RF input (and S-meter deflection) was measured on 14050kc/s
for Drake R-4C (87.05.18).

RF input voltage S-meter deflection AGC voltage RF input voltage S-meter deflection AGC voltage
0.1ÁV
0.3
S1
S3
-1.9
-2.6
30
100ÁV
S9+20
S9+30
-10.2
-12.8V
1.0
3.0
S5
S7
-3.6
-----
300ÁV
1mV
S9+40
S9+50
-16.3V
-22
5 S9 -5.8 3mV S9+55 -25V
10 S9+10 -7.8 10mV S9+60 -28V

So it seems to be just very useful for the amateur who need deflection to justify the 59 report.
I made a s-meter converter trying to improve the s-meter deflection using MPSA93 and uA741.




One of my attempts for better adjustment of S-meter deflection and proper time-constant for the meter.
The first used 4N28, but it had too much drift over the time, so I used MPS-A93 instead since they were
readily available. It is connected to the 6BA6/EF93 IF output valve.


Drake (R4245) Multimode quadrature detector (AM/SSB) (50kHz) with MC1496, see page c11


Circuit diagrams and list of the different versions of R-4C is shown on http://bama.sbc.edu/drake.htm




Es stand in der CQ-DL, Band 2, Testberichte
A really very interesting book from DARC showing testreports by DL1BU for the following equipment:
Atlas 210/215, CRF320, Drake R-4C, Dressler D200, FT-221, FT-301, FT-901,
IC-202S, IC-211, IC245E, IC-280E, IC402, IC-701, KDK FM 2015R, KDK FM2016E,
LT470 (Braun), Multi 2700, REIS SE200XL-A, SB-104, SE301 (Braun), TS-520, TS-820,

Vergleichtest FR101, FT-220, FT221, HG70D, IC201, Multi2000, Multi2700



Drake R-4C 22000-up
Last update: 2004.01.19