The R4B/T4XB Saga

The following information is provided to those of you who 1) like a challenge, 2) enjoy wielding a soldering iron, 3) who have free time on their hands and 4) may be in therapy for an obsessive complusive disorder related to ham radio.

It all started innocently with a perusal of the classified ads where I spotted an R4B receiver that was priced at $100. OMG this is what I was waiting for --Boom a few emails and some paypal and it was on its way. Well it had a few problems and an extra hole or two and a moderate amount of unorthodox modifications. You know what they say about fools rushing in --at times they get the best seats --but not in my case and as usual my bargain find took some time to first identify what had been done and secondly to make the repairs. I am happy to report that it is working and I am a happy camper. In some further correspondence with the seller I purchased a matching T4B Reciter. That one save for an extra hole in the panel was unmolested. With a bit of luck and some de-oxit on the sideband switch I now had a working station. But then there was that darn contest weekend where I worked a few DX stations but the really difficult ones were operating split --something not easily done with the T4B Reciter as it lacks a PTO and is slaved to the R4B. Thus another round of emails and for another $100 I had a "Tech Special" T4XB. Well calling it a tech special is being kind.




I should back up and mention that nine (09) combination R4B/T4XB's, one set for each band, were installed in a club station (W9IMS). Each pair was heavily modified and most of the mods were to facilitate and customized for CW operation. My pair were part of that installation.

I strongly recommend the purchase of a B Line CD from Garey Barrell This CD is chock full of all of the information needed to work on the B line. It was an invaluable tool when I worked on the T4XB. I did not have it when I did the R4B repairs. If I had the CD when I fixed the R4B it would have saved me lots of time and grief.

On my T4XB there was an extra control on the front panel, something to do with the vox time constant. Several of the controls were relocated such as the delay pot was moved to where the microphone jack was located which was moved to the back panel and installed where the CW jack normally sits. The CW jack was now two RCA connectors mounted in the vacant holes next to the power plug. The auxiliary crystal switch was now used as means of selecting CW1 or CW2, as associated with the two RCA jacks.

The electrolytic can which houses C129/C140 was removed and metal plug was fitted to the chassis and two separate electrolytic's were installed on the underside. I am not sure how the T4XB worked after that because C140 was installed not to the cathode but to one pin over --the filament. Given that today's circuits employ low voltage, I panicked when I thought how in the world am I going to find one of those metal can multiple value electrolytic's to replace C129/140? Well not to worry as there is a wonderful small company right in the middle of Iowa (not sure if it really is in the middle) that custom manufactures replacement type multiple value / multiple voltage electrolytic's for the vintage radios. That company is known as Hayseed Hamfest run by Tom Farland, N0JMY, and his daughter Dee Dee, KD0PHV. You can find them here:

Tom and Dee Dee do business the old fashion way where the customer is first! It was truly a pleasure to do business with them. The technical help was superb and the the follow up amazing. I got a follow up email from Dee Dee confirming my order and notice that the replacement C129/C140 had shipped. Three days after my first contact, the part was in my hand. They even included a chunk of de solder braid in the box. That was indeed fortunate! My cap was missing so not required for the removal; but I sure needed that solder braid when I was replacing the TR Relay. There are a few companies that truly understand customer service and I rate Hayseed Hamfest near the top. Thank you Tom & Dee Dee.


The TR Relay was removed and in its place was a large relay that was cable tied to the chassis and Board 6 had its mounting feet cut off and was sort of soldered to a large copper wire and more or less floating. The electrolytic that replaced C129 was cable tied to Board 6 and the copper wire anchor. One modification I guess was for convenience or there was no access to the two pin power plug to switch an external amp. The wiring was removed from Pins 5 & 8 on the power plug and was routed to an RCA Jack that was fitted in the "Spare" hole near the vox delay pot.

Tech Special T4XB

I also observed that there were a few burnt components and also by observing the solder connections on the various sub-boards I could more or less tell what was touched after the radio left the factory. In all I replaced 20 resistors and about the same number of capacitors. These replacements typically were to address burnt resistors, missing parts, parts way out of tolerance and parts such as mylar and electrolytic caps that have exceeded their life time. For good measure I replaced the two cathode resistors with ones that are matched. Later when I got the T4XB so it would output I found that on two bands (10 & 15M) there was no output -- a close inspection of one of the switch wafers revealed that connections for these two bands had been neatly cut but left in place. It was not until I moved the wires with a tip of a small screwdriver did I discover there was no connection. Shown below are the parts replaced or removed.


I would like to spend some time on how I replaced the TR Relay as this may be of interest to all who have the T4/T4X/T4BX with the OEM wired in relay and are faced with a replacement. This is also the case with the TR3 and earlier TR4's. The T4XC and the later TR-4's used plug in relays. I understand that the OEM relays were 110 VDC relays and there was a problem with coil failure. The Plug In Type Relays are 48 VDC and the change in coil voltage is accommodated by a simple wiring change at the 6EV7 where the relay wire is shifted from Pin 6 to Pin 9 and a 1.5K 2 watt resistor is installed between Pin 6 and Pin 9. The OEM relay was installed in a well area in the chassis that was formed by the base plate used to elevate and support the tune and load capacitors. Installing a replacement relay in this well area is like making out with a 400 pound woman in the backseat of a 1970 VW Beetle --possible maybe, probable not likely. So my solution is to mount the replacement relay on the bottom side of the chassis with the relay in a horizontal position extending over the well area.

The replacement plug in relay is physically smaller than the typical "ice cube" type relays which is good from a fit standpoint but not so good as the relay socket is small and care must be taken in soldering wiring to the socket. The Mouser Part Numbers for the relay, socket and spring clip are as follows: Relay R10-E1Y4-V2.5K, Socket 27E126 and the Spring 20C250. The total cost for these parts are about $30 less shipping.

In mulling over the problem of installing the replacement there were several concerns that jump out at you. The first is how to locate the relay so that the unit can be plugged in and out (any future replacement) and secondly how solder all of those wires in a very tight space. The answer is a two piece mounting bracket. I made the mounting bracket parts out of a piece of a Radio Shack Aluminum Mini-Box that I had sawed off to make a smaller box for some long ago project. This metal is really soft and easy to work with hand tools such a small electric drill and some fine files. The main bracket is in the form of an L and is approximately 1.5 inches tall by 1.25 inches wide and the base is 5/8 inch. I cut a rectangular hole in this part of the bracket so that there would be sufficient clearance so that the relay contacts would easily pass through this hole without shorting to the metal bracket. The second plate is about 1.25 inches by 1.25 inches and this is used to provide the base plate for the relay socket. Pretty clever how the socket is made as it has two raised areas, one for the contacts and the second for the power wiring. In between these two raised areas is a hole through the socket base plate and that enables anchoring the socket to the metal plate.

An alternate to the aluminum is to use the same approach with double sided PC board only that would require three pieces as the L bracket would be fabricated using two pieces. The double sided board would enable soldering the ground shields directly to the board. When cutting, sawing or drilling the copper PC board use a dust mask. K&S Metals sells small pieces of aluminum that would be suitable for this project and is avaialble in Hobby Stores and hardware stores.


Relay Installation

Note: Links to these photos provided below.

Now is the time for the "Ahahhh" moment! The reason for the two plates is the first is put into place while there is plenty of access to the area. Note that the mounting of the bracket is offset so that one 4-40 nut and bolt picks up a vacant hole along the side of the bracket and another 4-40 is at the front of the well. This adds structural stability to the mounting. Now the real bonus to this method. The wires are passed through the back side of the mounting plate and are soldered to the socket plate out in the open where there is plenty of access. When the wiring is completed then the socket base plate is moved into position and bolted to the base plate. There should be sufficient excess wiring to do this. My wiring was modified to accommodate the first replacement relay and may actually have been cut shorter. Shown below is how I wired the relay. I was going to include a wire color matrix but I understand that Drake frequently used different color of wires so that may not be useful. But what I have shown is where the wiring goes to / from the relay and that should help identify the correct wires. Link to wiring diagram for download. Questions: contact me at . Al, W8UT pointed out that it would be nice to see the detail of the relay install. Click on the links below for the large photo files.

* Relay Bracket

* Socket Bracket

* Fit Check of Bracket and Relay

* Relay in the socket

* Final Installation

* PDF Copy of this Webpage (Courtesy of Ed Tanton --thank you Ed.)


This was a fun project and the radio has been air tested on several bands so I know the repairs have been successful.

de N6QW