EB5AGV's TR-4C restoratiom

Keep them glowing!

This page is devoted to the repair of my second Drake TR-4C transceiver.

I got it in unworking condition, with a homebrewed AC-4 power supply clone.

Unit as received

As you will see, this TR-4C was in somewhat sad condition, mainly very dirty.

This is the AC-4 power supply clone:

It has a nice fuse set on the rear panel:

Cleaning and straightening

So first work was to clean it, starting with a vacuum cleaner. Previously, I carefully removed all tubes. Here you have some pictures of the chassis once cleaned:

Then it came some mechanical work, as it had a damaged connector in the rear panel:

And after some work:

Finding modifications

It was not hard to find some mods done to the unit. Some were cleanly made, some were not so clean.

First mod: XLR MIC connector. Function: MIC connector replacement

Second mod: extra diode and capacitors. Function: unknown

Third mod: extra potentiometer instead of blanker ON/OFF. Function: RIT

Fourth mod: non-original relay. Function: replacement

Fifth mod: non-original protection light bulb. Function: replacement

More cleaning

After chassis was in decent shape, it was the moment to take the front panel out. Once buttons were out, there was some yellowing clearly visible on the panel:

Here you have the naked TR-4C:

So I proceeded to clean it, using first alcohol and then a soft polish paste and this is the result:

I also cleaned the knobs with an old teeth brush and shampoo.

PTO works

One thing which was evident when I got the unit is that PTO was 'losing balls'... as I found a couple loose inside the box and PTO knob had lots of play. In order to fix it I needed to get the PTO out of the chassis. First thing I did was to remove PTO cover... and then I found the reason for the new front panel control:

Yes, green wire goes to a resistor/diode/capacitor network which should be the RIT mod.

Anyway, I let that as-is, because I was interested in the mechanical repair. So I got out the PTO and found a messy oily gearset...

After lots of work, I ended with a clean unit:

Thanks to Garey K4OAH, I had spare balls to fix the PTO but it was impossible to get an smooth PTO movement; it seemed something was missaligned, as I could only get 9 balls in (it uses 10) and then not all were contacting the race same time. So I got out the electronics of the PTO. It is not too evident in the picture but, as the red reference line shows, there was some weird angle in the PTO ferrite, which should be straight.

So, with some hesitation, I tried to get it straightened... and then I could put the 10 balls without problem and, once the adjustment screw was tweaked, PTO moved smoothly :-)!

So PTO was ready to go back to the poor PTO-less TR-4C chassis:

Tube cleaning

One thing I always enjoy when working with tubed gear is the tube cleaning... getting back the bright of glass tubes, of course preserving their labels, is a rewarding job. So I did it :-)

This is one 6JB6A tube as it came from the rig:

And then after some careful work:

Cleaning tubes is useful also to find problems on them... as this crack I found in one of the 6JB6A :-(

I guess I need a new set of power tubes...

Crystal cleaning and rig dating

Yes, there is a relation... in the base of some crystals you can find manufacturing date (month-year) so, besides the nice looking after cleaning it with metal cleaner, I found this February 1973 date in the 100kHz calibrator crystal:

Putting back front panel, crystals, tubes and knobs

Once crystals, tube shields and tubes were clean, they went back to the rig (except for the power tubes, as one is broken):

And this is the aspect of the front panel:

And this is the rear panel:

More to come soon as work continues. Keep tuned!

To be continued...


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