Drake R4A Communication Receiver

Early & Late Version

By WA9TGT / Donnie Garrett

12-28-2000

 

I wish to express my thanks to every one who responded to my R4A Serial Number Survey request!  The response was very good and was most appreciated!  I now wish to share the R4A serial number survey and make a few comments concerning the R4A receiver.

 

As many of you know Drake made 2 versions of the R4A receiver.  The early version was a 13-tube design and the later version was an 11-tube design.  Having both, I can not tell any noticeable difference in performance between the 2 versions.  If I have noticed anything at all, it’s just a slight difference in the sound of the audio coming out of the speaker.  The later 11-tube version seems to be just a bit higher in tone. I have listed the tube line up (shown below in table 1.1) for both versions of the R4A.  The R4A serial number survey is shown at the bottom of this article.

 

Table 1.1

R4A  (13 Tube) Early Version)  11/65 V1-12BZ6-RF Amp V2-6HS6-1st Mixer V3-12BE6-2nd Mixer V4-12BA6-50KC IF Amp V5-12BA6-50KC IF Amp V6-6GX6 Prod Det/AF Amp V7-6EH5-AF Output V8-6HS6 Pre Mixer V9-12BA6 50 KC Amp/NB V10-12AX7A-NB/Pulse Shaper Amp V11-OB2 Voltage Reg V12-12BA6-Xtal Cal V13-12AV6 –AVC Amp/Rect

R4A  (11 Tube) Late Version 10/66 V1-12BZ6-RF Amp V2-6HS6-1st Mixer V3-12BE6-2nd Mixer V4-12BA6-50KC IF Amp V5-12BA6-50KC IF Amp V6-Not Used V7-6EH5-AF Output V8-6HS6 Pre Mixer V9-12BA6 50 KC Amp/NB V10-12AX7A-NB/Pulse Shaper Amp V11-OB2 Voltage Reg V12-12BA6-Xtal Cal

 

 

In 2 areas, there are some significant differences in circuit design between the two versions.  Viewing both versions from the topside, you will find that everything appears to look the same except for the 2 extra tubes in the early version.  Both of these tubes are located in front of T-10. The closest tube to T-10 is (V-13) a 12AV6 which serves as an AVC Amp / AVC Detector.  The second tube (V-6) a 6GX6 sits in front of the 12AV6.  V-6 functions as a Product Detector / Audio Amp.  Both these circuits were replaced with a combination of transistors and diodes in the later 11-tube version.  The 11 Tube version used a pair of 2N3394’s (Q7 & Q8) as the 1st AF/Amp, and it also used (2) 1N270 diodes in the product detector circuit.

Also you will find that in the earlier 13-tube version, Drake used a pair of 2N3858 transistors in the PTO circuit as the Oscillator and Buffer amp. The PTO was changed in the later 11-tube version to use a 2N706 Oscillator and a 2N3858 Buffer amp.  Both versions incorporate bipolar transistors.  Drake switched to a FET as the PTO oscillator in the R4B receiver.  In an effort to obtain even better stability.  I have experienced very few problems with the R4A PTO design.  Most all R4A’s seem to settle down after an initial warm up period. The biggest problem I have found is that the mechanical parts of the PTO have become dirty.  This can often lead to mechanical and electrical problems.

 

If you take 4 or 5 different R4A receivers there will always be one or two that tend to be slightly better than the others as far as stability goes.  I also have had similar experience with the TR-4’s.  Actually, Drake did a good job of temperature compensating their PTO’s.  Some just turned out a little better than others.

 

All but one of my R4A’s that I have purchased had various problems.  These were problem’s that quickly surfaced after just a few minutes of use. I once purchased a so-called good working R4A (according to the seller) only to quickly realize how sick it was after I brought it home.  I don’t think the person I purchased it from actually realized how bad it was.  I soon began to resolve each problem one at a time, slowly restoring it back to as near perfect operating condition as possible.

 

All in all a proper working R4A receiver whether it be the early or late version is a superb receiver.  The R4A’s are quite often passed over in favor of the R4B.  My suggestion: Give the R4A a try.   It’s a great receiver when working properly!

 

R4A Serial Number Survey Results

 

 

SN#                  Version            Manf Date

 

2007                 13 Tube              Date (11/8/65 per schematic number code) Garey K4OAH

2019                  13 Tube              Date Unknown Joe / K9DMV early 1966
2143                  13 Tube             Date Unknown Tim / WB8OWX
2250                 13 Tube             Date Unknown Gary / W8PU

2304                 13 Tube             Date Unknown Jim / W8DRZ

2387                 13 Tube             Date Unknown            Chuck / K1KW
2781                  13 Tube              Date circa 1965-66 Harold / NY7Y Original Owner

2847                 13 Tube              Date Unknown Don / WA9TGT

2872                 13 Tube             Date Unknown Tim / WB8OWX

2912                  13 Tube             Date Unknown Dean / KA6BGW

2992                 13 Tube             Date Unknown Al / W8UT

3234                 13 Tube             Date Unknown Mike / W3MC

3679B               11 Tube             Date Unknown Al / K0AL (I am awaiting reply on version conformation)

4054                 11 Tube             Date (8/25/66 per schematic number code) Garey K4OAH 

5036R               11 Tube             Date Unknown Don / WA9TGT

5057R               11 Tube             Date Unknown Jim / W8DRZ

5140                  11 Tube             Date Unknown Dave

5289R               11 Tube             Date Unknown Jim / W8DRZ

5398B               11 Tube             Date Unknown Tom / DF2OO

5407G               11 Tube             Date 10-21-66 Don / WA9TGT  (still has manufacture tag)

5667G               11 Tube             Date Unknown Don / WA9TGT

5822R               11 Tube             Date Unknown John / WA4OGD

5839R               11 Tube             Date Unknown Don / WA9TGT

6047G               11 Tube              Date Unknown Sindre / LA6OP
6051G                11 Tube             Date Unknown Don / WA9TGT

6087G               11 Tube             Date Unknown Gary / WB7FCQ
6357R               11 Tube             Date Unknown John

6620B               11 Tube              Date Unknown Sindre / LA6OP

6966B               11 Tube             Date Unknown Jack / WA9NQW