Well I spent a littl time with the R4A this morning. First, no tube swaps with the R4B yielded any improvement. Strangely, some even made the R4A LESS sensitive. Don't know what that says about the tubes in the R4B, but I think it really means all the tubes are pretty much fine.
I did try the timmers, using the XTAL oscillator as a signal source, that did not yield any improvement, they were all already "on". I did check TP2 and its associated adjustment resistor under the chassis, that too was already fine, though it does highlight I do need a much higher impedance voltmeter than the one I have. I did use deoxit on the RF and AF controls, the wafer switches, etc., that yielded a BIG improvement in overall operation, though not sensitivity. While the R4B does seem a bit "hotter", and it's "S" meter is more responsive, the R4A is definitely OK, not way off like I had thought. I think what it comes down to really is, the Friday evening I received the R4B and hooked it up, the bands were in fairly exceptional condition, in these days of unexceptional band conditions. That's really what it comes down to. Even the airport weather around 10.1Mhz, the Saturday right after I got the R4B, several stations were booming in on that frequency, as was WWV at 10Mhz, while this morning, for contrast, WWV was there but not strong, and I could not hear the weather stations at all. Chuck, K1OM On Sat, Apr 18, 2009 at 1:44 PM, Chuck Grandgent <ch...@chuckg.com> wrote: > Excellent suggestions, all. > > I'm going to print them all out and go through it methodically. > I do have a URM-25D in good calibration. > So I'll make some notes as I go along, and note its performance before I > muck with it. > > I do feel a bit foolish, when I got home and unpacked it and powered it up, > I guess band conditions were very good, a bit quieter on the bands this > morning :) > > Thanks to all, > > Chuck, K1OM > > On Sat, Apr 18, 2009 at 10:11 AM, Garey Barrell <k4...@mindspring.com> > wrote: >> >> 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 >>> >>> >> >> _______________________________________________ >> Drakelist mailing list >> Drakelist@zerobeat.net >> http://mailman.zerobeat.net/mailman/listinfo/drakelist > > _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
