All Things Wireless & Letterpress

All Things Wireless & Letterpress

Friday, June 12, 2015

Resurrecting the Drake TR-3 and AC-3 Transceiver and Power Supply.(Part 2)

Having finished the AC-3 power supply, and upon being satisfied that it was operating to specifications, it was only natural to try it out.  I already had an idea of what would happen, but I plugged the supply up anyway, attached it to the TR-3 via the big Cinch Jones plug, ramped her up, and voil'a!  

Pop, snap, fizz.  And a mild aroma of ozone filled the air about me.

There is no doubt that the TR-3 was dead.  This must be distinctly understood, or nothing wonderful can come of the story I am going to relate. The relay would not key.  The lights would not illuminate.  Smoke whisked from the audio section.  Various sparks flew from the Vox and Anti-vox potentiometers.  Nary a sound made it's presence known through the headsets.  Not so much as a hum.  The TR-3 was as dead as a door nail.

Mind!  I don't mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail.  I might have been inclined, myself, to regard a stripped cabinet screw as the deadest piece of ironmongery in the trade.  But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country's done for.  You will therefore permit me to repeat, emphatically, that the TR-3 was as dead as a door-nail.

Not being one to follow a straight line, even with coloured pencils and Magic Markers, I set about to do what most geeks like me do when we don't know what else to do: hunt down all the paper, moulded and electrolytic capacitors / condensers, identify their values and replace them.  And to be sure, this is Standard Operating Procedures.  It's not that these capacitor types might be bad, the are bad!  The results were to reveal that such was no more so than it was with the TR-3.

The truth is, there really are not that many to replace!  There are five paper caps and two electrolytics, almost all types the same value.  The papers were replaced by polymer and one orange dip, and the electrolytics were replaced by new electrolytics.

All of these caps are found on small upright phenol boards mounted either near the side of the radio where the control pots and jacks are (Vox, Anti-vox, Meter Zero, Mic, Headphone and Key jacks) - or center rear.  The paper caps are pretty obvious,  they are identical white tubular types, all 0.47 uF save for one, which is .01 uF.  The above photo shows their appearance and the boards they are mounted least, in the early model TR-3s.

The ideal removal tool for these components is a small flush cutter.  The following describes the technique I used to replace them :  I cut them out by cutting their wires as close to the component itself as possible.  This leaves the two original wires soldered into place.  These wires will serve to mount the new component by providing something to solder to without disturbing the original solder.  I found over the years that things go a lot better if you avoid disturbing original terminal solder connects.  That is, if they are good solder connects!

Now, most of these boards can be removed, but go slow. If you can, keep a digital camera that can do micro-zoom handy.  Almost all of the inexpensive digital cameras like the Canon Power Shot will do nicely.  I recommend this because not only are these boards held in place by one or two bracket screws which must be removed, but they are also hard wired to adjoining circuitry at multiple points.  Most of these wires must be cut.  As you cut them, leave them in position so you can re-align them with the wires on the board when you re-install them. 
As you can see from this example, the vertical board is held in place by two angle brackets screwed to the chassis, and is also soldered into place by 20-gauge bus wire, plus insulated wire leads.  These insulated wires are not necessarily colour coded, so be observant!  Take good notes, perhaps do a drawing, or best, take a photo.  Digital camera technology is your friend here!  Digital Cameras are part of my restoration tool-box.

 Be sure to photograph, or at least make notes on the wire attachment to each side of these boards!  There will be bus wire cuts, insulated wire cuts and component (resistor/ ceramic disc capacitor) cuts that will need to be re-attached.  I might add that there were two boards whereas I found  I could leave the wires intact, requiring that I simply remove the bracket screws and lift the board a bit.  All I need to do is snip the cap out and have sufficient room to re-solder a replacement component into place.

I wanted to show this photo.  The smoke I mentioned earlier came from this 3.3k half watt resistor which bridges these two component boards.  There was an associated ceramic disc capacitor on the other side of the board, a small bypass cap, that had shorted, creating a path to ground that permitted too much current for this resistor.  In these tube type Drakes, you want to be mindful that they create a lot of heat in confined areas where ventilation is limited.  Many owners will mount muffin fans on the cabinets to force additional air exchange, which isn't a bad idea!

Convention almost implies that we be mindful only of replacing Paper, Moulded and Electrolytic caps. The tendency (and often read written opinion) is to leave the ceramics and silver micas alone.  I say look at everything!  There IS no hallowed component.  They are ALL prone to failure with age.  It doesn't mean you go out replacing all the caps, but don't assume all ceramics and micas are innocent or somehow unaffected by age, time, and heat.  Pay attention to any associated resistors.  A brown or discoloured resistor is your clue to higher currents, which may be due to either a value change in that resistor due to age, or a high current short nearby - normally a cap.  And, beware of strictly going by continuity checks alone.  Most of the shorted caps in my experience showed open continuity on a VOM.  However under high voltages and operating currents, these opens will close!  As such, do not be in a hurry, and keep your variac handy.

 BTW, I replaced that 3.3k resistor three times until I figured out what was going on.

The technique employed here involves the use of Squigs, or "Pig Tails" as we used to call them.  I already made a blog entry about the use of these items.  At one time you could buy them, but these days, I make them from 22 gauge tinned bus.  For details, visit my corresponding blog entry "Resurrecting a Drake TR-3: Pigtails!"

Here is a shot below deck showing the replacement caps having been "squigged" into place utilizing the original wires that were left soldered to their terminal points. You may have to click on the photo to get a good look at these solder connections.  Note the rear boards are not yet bolted down. I was still in the process of squigging their connections back together.

Touching on other things that were going on besides the circuit work, I pulled every tube/ valve, every crystal, one by one and gave them a thorough bath of DeOxit.  You can see the bottle in the photo with the hypodermic cap.  Relays, sockets, any place where metal contacts metal is treated to a liberal dose of DeOxit.

The white metal covers that cover the mA meters and the planetary dial were removed, sanded, repainted with white semi gloss, and replaced.  Possibly a better choice may have been flat white.  But no matter, the blue dial filter (acetate) diffuses any light bouncing around behind the dial.  Make sure there is electrical contact with the slide-on light bulb sockets. Those areas might be best sanded to ensure grounded contact with the bulb holders both for the dial and the mA meters.

Accompanying these activities was the treatment of the cabinet.  The cabinet was awful.  The TR-series Drakes use a clam-shell cabinet which is held in place by twelve machine screws - six for the top, and six for the bottom.

I opted to do the wrinkle finish on the top, and use flat black for the bottom, just to provide an interesting visual break.  I did the same combination when restoring an enlarger, and it was quite attractive!  To read more about how handle wrinkle finish treatments, refer to my prior entry concerning the rebuilding of the AC-3 Power Supply. 

It takes about twenty four hours for the wrinkles to "set" to the point where the cabinet sections can be safely handled. As such, a lot of patience is required. This patience is amply rewarded once the project is completed!  I think Drake should have used Wrinkle Finish too. Again, just my opinion.  I have a lot of those.

Here is another view of the cabinet, under natural light.  All sides wrinkled very nicely owing to the even distribution of heat due in large part to the ventilation holes.

Wrinkle Finish is like a letterpress printed piece.  You have to behold it up close and touch it to really appreciate it.  Wrinkle Finish provides a very robust, tactile surface that engages not only the eyes, but the sense of touch.  This is why I especially like to use it, when appropriate. 

Up to this point we are finished with the circuitry, we finished  the de-oxidation, we finished painting the inside and outside metal work, we also replaced the feet.  What next? her up!

I loaded her into a 60 watt bulb to see if there was anything like output.  And yes!  As it turns out, she is willing to yield about 100 watts cw, and later when I tested her on SSB, about 120-150 watts on voice peaks.  Her finals are old, but are themselves, replacements.  I suspect they were replaced sometime in the 1980s.  I have the originals, where are blown, with cracked glass. 

Here she is, all buttoned up and ready to be parked next to the 2B.  My intention from the start was to use the TR-3 as (gasp!) a cw transmitter!  This was because I had no idea that she would ever speak with a voice again!  She performs marvelously in this capacity!  Flipping her over to cw position, she immediately emits a very weak signal perfect for spotting.  Since this is in transmit mode and the changeover relay is already in transmit position, I can start sending immediately.  When I switch back to the 2B and switch out of the cw position, the spotting signal ceases.  Having grown up with home-brew transmitters and separate receivers and never owning an RF activated ATU in my life, I am used to flipping switches between transmit and receive.  Part of what geeks do!  I did the same with that Gonset shown in the video and one of the photos  which . . . is no longer there as of this writing.  It is now comfy in it's new home at AF4Ks shack.  The Drake is now filling her shoes, and quite nicely so!

A few things still need to be done with the TR-3.  I need to re-wire the filament voltage to the mA meter and dial housing pilot lamps.  The sideband selection switch lights are, however, working fine.  The mic gain is a bit crackly, that will be ultimately replaced. I would like eventually to find a new face plate, too. The TR-3 is, however, dead on frequency.  The power supply is running smoothly.  I do wish to, eventually, replace both mA meters.  It is not uncommon for the d'Arsonval movements to become magnetically gaussed and sticking.  I have to tap the S-meter to break it loose from it's internal magnetic charge.  The rig's mA meter simply isn't working.  All tuning is done using the metering on my Dentron MT-3000A.  But again, I am used to meter-less rigs.  

So, there she is.  But the story isn't over.  What about phone?  

I had thought to let that go.  But curiosity got the best of me.  I did not have the proper plug for the mic jack,  and honestly, I was tired of having to mail order everything.  Our local MilSurp store which used to have bins of these connects had none.  But since I was there, I purchased a 1/4" jack, and retrofitted the original.  Of course, I am keeping the original to replace when the time comes.  But at least I was able to wire up the Shure 444 mic and give her a spin.

And spin it did!  Wow!  ....and talk about great reports!  As of this writing I have worked quite a number of stations under sorry band conditions, all on forty meters, and all say the same thing : the voice "punches" through!  AF4K reports that this TR-3 is a "DX-machine!"   Signal reports aren't bad, either.  As I said, I am seeing 125 - 150 watts on voice peaks.  That's low for these rigs, but the tubes are old, too.  

Hey!  So long as nothing smokes!

The receiver is awesome.  I suspect the passband to be around 2kc.  Upper and lower sideband filters are performing fine.  I might address the carrier null, but it is fine as it is.  Just a wee bit of carrier heard through the HQ-170.

So, there you have it.  The "Resurrection" of a TR-3.  Satisfaction level from 1 - 10: 12.  She is QRO and Go, both SSB and CW.   What about AM?  Well . . . that's for another installment.  My coffee is getting cold.

vy 73 es God bless u es urs!

de wd4nka

(BTW: I published this soon as I was done with only cursory proof reading.  If you find blatant, glaring grammatical or factual errors, check back again.  I proof read these after publication and edit them over time  because, well, that's me, I guess.)


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