Chuck -
Depending upon the s/n of your R-4A, the two receivers are almost
identical, electrically. So there is a reason for the apparent difference!
1. Check the voltage, with a HIGH-Z meter, (not a cheapy DMM,) at
TP-2. On top of the chassis, under the Passband Tuner shaft. Should be
-1.35 VDC, and this sets the sensitivity of the receiver. If you have
done AGC work, you probably know this, but ...
2. Check that the S-Meter ZERO is correct, and that the meter reads 60
dB over S9, (full scale,) with the RF GAIN at full CCW.
3. Most likely weak tubes are V4 and V5, since this is where most of
the receiver gain is.
Finally, one of the "problems" with the Drake receivers is their
excellent AGC system. The basic system is so good, that ALL signals
seem to be at about the same level in the speaker, and you have only the
S-Meter to tell you which are the strong ones and which are the weak ones.
Really the only way to compare the receivers is with a calibrated signal
generator. I really like the little XG-1/2 by Elecraft or the S9 by
NORCAL. Both give you a known 1 uV signal ( ~S1-2) and a known 50 uV
signal (S-9) at various frequencies. You just have to tie a long piece
of yarn or something to them to keep from losing them on the bench!
You can do a touch-up alignment in about ten minutes, using the
Calibrator and the S-Meter. Typically the transformers do NOT need
adjustment, and a simple peaking of the trimmers for the RF, MIXER and
PREMIXER stages are all that is needed.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Chuck Grandgent wrote:
Well the purpose of this post is twofold:
First, despite periodic negative reports about the eB** place, I
wanted to report my just received acquisition of a very nice R4B.
Decent price, decent shipping charge, very well packed, nicely bound
copy of the R4B manual plus misc other relevant R4x articles, received
approx three days from the end of the bidding (USPS Priority). I don't
recognize the call from being on this list, so I won't identify unless
there's a reason to. In short, I couldn't be more pleased.
The second reason for the post is about my R4A, and the diff between
it and he R4B.
I have to say, I have been happy with the R4A over the appro 10 years
I have owned it. I have had to do a fair amount of work on it in the
AGC section, but I have done lots of great QSO's with it. And to be
fair, it lives in my garage, here in No. Florida, and what with the
heat, humidity, and insects, it has not had an easy life.
Anyway, my first impressioin on powering up the R4B is, that it is SO
MUCH MORE SENSITIVE than my R4A, including the S-meter response.
Nevermind that the switches seem a lot cleaner, the tuning knob spins
easier, etc..
So anyway, I wanted to ask, where would you first begin to look in the
R4A to account for the difference in sensitivity between it and the
R4B I just got ? I have checked all tube pin voltages, and they do
agree closely with what they should be, and I believe the tubes are OK.
Chuck, K1OM, Alachua, FL
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