Drake T4XC

Yup, that is my main transmitting rig. Older than sin but still works and looks good. It is also not stock, or maybe some would say ‘mint’. It has been modified in several ways but the main mod is a conversion to use 6146Ws in the final cage. A minor mod is the addition of a fan to cool the finals but that has been disconnected because I got tired of listening to the fan noise. Not that it was all that noisy but I could tell it was on because the shack is otherwise quiet as a tomb. I finally realized that the finals would not be on but for a few minutes and even then would not be running flat out so the additional cooling was not really necessary and I would appreciate the quiet much more.

This transmitter gets used at least once a week on 75 meter SSB.

Recently I found an additional mod for the Drake T4X series of radios. An audio modification claiming to make the audio easier to listen to. Make it more natural sounding and of HI-FI quality. Well, I never have taken much stock in striving for HI-FI on the ham bands but I took an interest because the mod included a simple addition of capacitors in the mic amplifier circuit.

Those not familiar with Drake equipment may not realize the construction and difficulty in executing any mods of this nature. All the T4 series of Drake radios uses small PCB boards that are mounted on-edge to the chassis. This makes it difficult to even see what is on the boards much less change anything.

It took the better part of a day just to find the manual. Then the entire afternoon to find the parts in question. The idea was to add capacitance to existing capacitors to improve the frequency response of the mic amp at the lower end of the audio frequency scale.

Turns out that my transmitter did not need the extra capacitors. It already had sufficient capacitors installed. Guess maybe it was a later model. What this excercise did disclose was that the 6AU6 AM modulator was disconnected from its PCB and a 100k resistor had been broken on another PCB. Obviously these deficiencies did not effect the operation on SSB lower sideband in the 75 meter band. Still, these deficiencies needed to be corrected and they were.

So now I can use the transmitter on AM if I want. That probably will not happen but it puts the spotlight on what might be problematic in the future. Every indication was that the lead that had been disconnected was due to fatigue of the wire in the soldered termination on the PCB.

Drake used solid conductor hook up wire on all their equipment. This works well but introduces the problem experienced. On installation should the solid wire be nicked even slightly before it is terminated to a connection chances are good that it will break sometime in the future if it is subject to stress. In other words, if you wait long enough, all the hook up wire in the radio will fall off when you remove the covers. Hopefully this may not happen for 500 years but I know of at least one wire connection that did not make it past 30 years.

So, although the repair was really not necessary, I am glad it was made and the rig is back to its normal self.

1 comment so far ↓

#1 admin on 02.17.09 at 10:55 am

Working well too. Last night tuned across several bands and calibrated the receiver and transmitter dials to agree with eachother. Now the radio can transceive on receiver or transmitter and still be on the same frequency.