No, this is not how you want your Drake - or any transmitter for that matter - to appear. No, it's not dead. It's just undergoing extensive "surgery." Prognoses for survival? I hope just fine, but it's been like this for awhile. At least a year now. Prior to that, off and on for another couple of years it's been belly up on the workbench. For a number of years it operated flawlessly. Good power out and smooth tuning on all bands. Good CW and voice operations. Yes, it even experienced some brief times on 10 m. AM. Most operation has been on SSB and CW, however. The problem started during a 15 meter CW QSO when a sudden "pop" and a stream of smoke cut

To compress history and make the story much shorter, a long series of small problems plagued the transmitter after that. Tuning problems, bad PA tubes and suspect components such as leaky disk capacitors. Output power when it would tune right often was on the order of 4 watts. A replacement pair of 6JB6 tubes enjoyed a short life. In frustration, I made the conversion from 6JB6 tubes to the more robust 6146 tubes. That did allow somewhat good operation for a short while. Little problems with tuning on some bands still haunted the rig.

Extensive troubleshooting sessions revealed some bad disk capacitors That's not unexpected. After all, the radio is perhaps 30 years old. I won't chronicle all of the details of the troubleshooting process but where we are right now is in the finishing stages of the complete replacement of ALL disk capacitors. Most of these are either serving as bypasses or coupling components. I have also replaced the electrolytic (it's a multi-section one) with new, individual caps. Note the blue cased one visible in the photo.

So, we have just a few more to go and I think that will finish the project. Will it work properly after that? I hope nothing more is required. I am not certain though as the power output level has degraded and now is rather low. The exact level on each band I do not recall as it has been close to a year since it's been powered up. On the same bench is the AC-4 supply all ready to go as soon as I am ready for a trial. Heeding some advice, the entire complement of electrolytic caps within the supply have been replaced. Voltage and o'scope measurements indicate that the power supply is ok.

An overdue update. July 21, 2004. The transmitter is now repaired and back in its rightful place on the operating desk. I'd be hard pressed to pinpoint the ONE thing that actually fixed it. I did replace all of the small disk capacitors which ranged in value from .001 to .1 mfd plus a couple of other values. Several of them looked to be defective, exhibiting some value of leaky resistance when measured with an ohmmeter. Since I completed this project, I have obtained a good capacitance/inductance meter. That instrument would have been helpful during the troubleshooting process. All metal to metal connections were examined, cleaned with DeoxIT and secured. That includes the tube sockets as well as chassis segments. Many solder connections were touched up as well. I also replaced all of the electrolytic capacitors within the AC-4 power supply. Again.

Following a complete alignment per the manual, power output on all bands was satisfactory. Power output in the Tune mode on bands 80-15 meters is about 110 watts. Power output on 10 meters is only 70 watts. I suspect that different PA tubes might bring that up. It's not enough of an issue for me to bother with, however. Key down power on CW is more. On the order of 120 to 130 watts.

After putting the transmitter back on the air, I received some audio reports which were less than desirable. The claims were that the audio, though it did not sound distorted and for that matter did not "sound bad" the quality had something of a harshness to it. That was noted by several different stations at different times, so they were independent judgments. I did try a different D-104 microphone but with the same results. I replaced some of the tubes, which had not given normal readings on my tube tester and realigned the radio again, paying close attention to the carrier balance settings. Subsequent on the air tests have reported good audio so whatever was wrong now appears to be resolved. I am a little disappointed in that I did not find a conclusive problem so I'm sensitive to the possibility of a reoccurrence. Hopefully that will not occur.

A couple of side notes. I've accumulated the parts and am in the process of building a two-tone audio generator for testing transmitter linearity. The tester is featured in the November 78 issue of QST. Sure, it's older technology but it will do the job quite well. Also, the capacitance meter referred to earlier is the L/C Meter IIB by Almost All Digital Electronics. http://www.aade.com/lcmeter.htm This is an indispensable piece of test equipment for any shack or test bench.

A note on the AC-4 power supply. In time, the original electrolytic filter capacitors are going to go bad. As the original style "cans " are nearly impossible to find today, some improvising in replacement is necessary. I won't cover all the schemes possible here. Some will go as far as to salvage the original capacitor housings by opening up and removing the original interior material and install new replacement capacitors inside those. That will of course serve to retain the original look of the device. I did not follow that path, though there is no reason not to do so if desired. Fortunately, no matter the reconstruction method chosen, modern electrolytic caps, for their electrical values are smaller in physical size than earlier versions. That does allow for either installing the replacements within the original housings or fitting most of them under the chassis. I installed as many as would safely fit, under the chassis. I had to remove one of the originals and in the space now available, mounted two of the replacement caps on top of the chassis. I mounted them upside down and secured them to the chassis with hot glue. I ran the connecting wires up from below through the hole vacated by the removed original cap.

No, the chassis no longer looks original but as the entire supply is enclosed within its own metal housing and the entire supply is enclosed within the MS-4 speaker cabinet, who's going to see my work? Likewise, the electrolytics replaced within both the T-4XB transmitter and the R-4B receiver are new devices tucked away below the chassis. The original cans were left in place preserving the original appearance of the radio as visible from the outside.

I also replaced the original 2 wire AC power cord with a 3 wire grounded one. Ok, so I'm tampering with originality.

Another Drake fan who prefers to remain anonymous (I'd like to give him credit otherwise) has provided the drawing of the layout of the AC-4 supply. This may be helpful to anyone considering the replacement of the original filter caps. Depending on the actual replacement devices obtained, different mounting schemes may need to be explored. Remember, on the capacitance values and voltage ratings, going higher in value is not going to hurt. You may have difficulty in obtaining the exact values as the originals. Don't go lower.

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Questions? Comments? Contact me.