TRK12/120 Restoration
 

For some very sleepy reason I originally posted this on antiqueradios.com.
I'm moving it to here, the right place.

I am still at the beginning of my project to make a TRK12
out of the parts I picked up at the 2015 ETF convention.

I have not even begun to work on the TRK-12 TV, whose two chassis
came in crates, looking "almost" new and virgin ... but not quite!
There are a couple of 1950s shiny 1/2 watt resistors in there.
We won't know how late it ever operated until it is turned on and
the oscillator frequencies are measured. I have all the necessary replacement
caps. This evening I measured a substantial fraction of the resistors
that can be measured The resistor markings are odd .. its mostly
body - end band - next to end band - other end band is silver 10%.
They are all high ... but less high in the 1k - 100K range than
higher or lower. Replacing most will be lots less cosmetic trouble
than expected ... I'll just repaint the closest physical size in modern
resistors. There are dogbone power ones. The Candohms will get
shamelessly replaced with modern resistors on terminal strips.
Well, I'll probably paint them if the paint
I got can take the heat.
Paper caps are ALL absolutely bad
but look nice and will be very easy to restuff. Almost all wire is cloth and OK.

The radio, an RC-427F one for a TRK 120, is in sad shape.
It got rained on. There was rust on the back which I thougtlessly
removed before a photo. Some coils are toast and will get modern replacements.
All paper caps are so fragile as to be unrestuffable. I have not decided whether to
make new fake shells (not easy!), or just use raw yellow axials. Half the wire
is cloth and probably OK, half is plastic and falling apart and will be replaced
(with cloth). The mechanical works are dirty but not rusted and all the turners turn.
It will get a brand new eye tube and mount (TRK120s had no eye tube).

The cabinet is not actually bad. It can be used as-is. A restorer is coming tomorrow to
look at it.

This is going to take a lot longer than last summer's CT-100.

Doug McDonald

Today's word of the day is unrestuffable :D.

Good luck on the resurrection Doug. Keep us posted and post those photos, every one loves photos.

Doug, I have a bunch of old paper capacitors you can restuff. Let me know what values you need.

I also have thousands of NOS prewar resistors. If you made a trip down you could go through them and probably find everything you need.

Here are photos of the TRK12/120 pieces, first set
of cabinet pictures. The last two are looking straight up,
camera sitting inside cabinet on bottom.

Rest of cabinet photos

First three are radio. other two are TV main chassis

The photos of the TV power supply. The radio power supply
is missing almost all parts.

Question is ... there is something missing in the mounting
for the TV chassis. It has been modified ... note the extra
holes in the front. These will be plugged and now veneer
installed covering them.

But where do the unattached wood pieces seen on the carpet go???
There is no way to install the TV chassis. Does anybody know?

The hole size and pattern look to match the chassis for an RCA 630TS. It doesn't make any sense why that would be mounted down there, but that was my first thought when I saw the photo.

Progress report: I've found a cabinet restorer and it has been sent off.

I've found all hard to find pieces and have all but the radio power transformer,
which is supposedly on the way soon.

I've been working on the filthy radio chassis, which is now cleaned up.
Most but not all of the push buttons and the motor work. I'm now cleaning
up the tarnished push button switches. I have not yet decided whether
to take McVoy up on his offer and get usable old caps to restuff for it.
I can restuff the non-polar electrolytic for the motor. Almost all paper caps in the radio are actually open!

Good luck Doug! Looking forward to following this restore here on VK.

This TV's radio has seen lots of work in the past. Last night I finally got all the push buttons to work. The problem ended up being a very odd one: the mounting for
the whole set had been bent and the latching mechanism was preventing some
contacts from contacting when pushed in.

Also I noticed something for the first time: the motor had been rewired with the wire put on by hand! Its clearly the later light colored Nylon wire and is all scrambled
up. Also all the connections to it had been hacked off and reattached in a very
nasty and unsafe manner. However, they did make it work right. For somebody with a pristine one, how long is it supposed to take to go from one end of the band to the other? Its slow but acceptable.

The cabinet is back from the restorer. He did, in my opinion, a very fine job.
He did, however, punt on decal placement, making me do it with his help.
It came out great. However, there were only channel numbers 1-5 so
that's all we used. I hope they are in the right places, the gap is at
far right.

Also ... are the hinges supposed to have a detent for the correct
angle? They sure don't seem to, though they stay put perfectly well.

Pictures eventually.

Sounds like you placed the channel numbers correctly.

There is no detent. The lid is designed to stay put at any position.

The restored cabinet.


http://www.videokarma.org/attachment...1&d=1434331611


http://www.videokarma.org/attachment...1&d=1434331611

Very nicely done. It has a smooth semi-gloss finish that looks very original. It's so fortunate that John Vassos was chosen to design these cabinets. They have a very clean machine-age deco design.

I just looked again at the pictures of my cabinet. The front-on
one is absolutely bizarre, I didn't notice! The left and right hand sides
are not symmetric in shade. But .. they most certainly are
quite symmetric in person. I've never before seen my camera
do something like this.

That is some really nice cabinet work!

I've notice Veneer tends to reflect light unevenly, probably because of the bands of grain, that's what makes it so attractive though.

Finally all necessary parts have arrived. Posted is a photo of the radio chassis in its current stats. That is, rust removed, missing the motor capacitor, and the Candohm and three brodcast band coils (hopeless) detached from their moorings. All paper caps are unrestuffable,
Steve McVoy has graciously sent me defunct ones with healthy cardboard cases. Most sections of the Candohm were long ago open and bridged.
Plastic insulation has crumbled. But the motor drive is fixed and works perfectly (with a suitable cap clipped in of course).

The flash of a camera can often bring-out things that cannot be seen under normal lighting. Sometimes it can really compliment a cabinet, other times it's unflattering to it.

Your cabinet looks very nice after the restoration work. What a contrast from when you started.

I'm 40% through recapping the radio of this monster. So far only one resistor
was over 18% high and it was 1.5 Meg rather than 1.0, the 6A8 2nd grid resistor, so I left it.The area around the can electrolytic is a nightmare so
I'm not restuffing it ... in any case no one will notice as their eyes will all be in the area of the former Candohm.

I am restuffing the paper caps, but even with McVoy's generous stock
of old ones I could not always use the original size bodies as some diameters
were too small. Nor do all the ends look right ... I'm wondering: will
painting the visible ends (which are hot glue) black with acrylic paint be OK?
Will it flake off?

Acrylic should be OK. Probably too late now, but you can get hot glue sticks in many colors including dark brown similar to the original wax.

I use a dark brown hot glue to hold the new capacitor inside the old shell. It looks very close to the original wax, but to get it to look even better I actually save the wax that I removed from the old cap. I fill the brown glue almost up to the top of the cap and then melt some original wax to "top it off" at the end. Using this method makes the re-stuffed cap look so good that I have to mark the caps I've replaced because I can't tell them apart.

Oh, man, that cabinet is "To Die For" pretty ! What does the CRT look like ? Its one of those 3-4' long jobs, isn't it ? You're STILL a VERY lucky man...

These are not wax caps. They are either the kind with the little paper
disk at the ends with the cylinder ends rolled over it, or paper tubes
sealed at the ends with some sort of black hard substance that
does not melt at a temperature low enough to keep the paper
the original hue. They can, however, just be pulled out.

I had to remove the volume and fidelity controls
to get to parts under them. I've decided to replace all parts under them
with new ones because this is such a hard chose.

I was able to leave lots of old rubber wires in the RF section alone
because they dangle quite safely in air ... but in the audio section
100% of the non-cloth wire will have to be replaced.

I got like three caps replaced today ... the rest of the time was spent
in disassenbly, rewiring, and having to go back to campus to buy
a new soldering iron tip since my local (5 minute walk) Radio
Shack was sold out.

The CRT is less than two feet long by a little. Its one of the
refurbished aluminized radar tubes. I have not taken it out of its carton.
I have a 12LP4 to use for testing.

I too am pleased with the cabinet. Except for the side
pieces of veneer on the front it was not in too bad shape overall,
just scratched, needing sanding. Also, there was a large chunk out
of the wood cover that fits over the CRT which needed filling in and
covering over with new (and very sharply bent) veneer. They guy was
able to match the original veneer closely enough that he didn't
need to redo the other side. Only the bottom front and back pieces
(plain wood no veneer) were badly water damaged and were replaced.

Little progress today. Two resistors replaced, two rotted wires,
and mostly repainting a whole lot of resistors. I painted the bodies tonight;
tomorrow morning I will paint the end and ring (these are not B-E-D
color code but B-E-ring). I'm using ordinary modern resistors, not
worrying about size as the set had a wide variety of sizes.

Doug McDonald

I got the radio working. 80% of resistors, all capacitors, and 40% of wires were replaced.

I first turned it on with no tubes at all inserted and nothing smelled bad, the
motor tuning still worked. Then I inserted the 5U4G and found that the second-level
HV was too low. It turned out to be what I worried about: I did not restuff the
electrolytics, but hid replacements. One was rather close to the fidelity switch,
and I was afraid to bend the switch contacts too much, so it shorted.

I unsoldered the offending switch lugs and redid them, leaving 1/8 inch
spacing which is fine for this voltage. This fixed that problem.

Then I removed the 5U4G and inserted all the other tubes. No heaters.
I had not used Deoxit on the plug that delivers power to the main chassis.

Then I tried running everything inserted on a dim bulb. Nothing smelled
or showed signs of a short. Setting the switch to TV or phono and touching
the input showed the audio worked.
Setting to radio and tuning around shortwave produced little (the broadcast band
coils are defubnct, that has to wait til tomorrow.) Attaching an antenna
resulted in absolutely normal shortwave reception!

:banana:

chassis pictures tomorrow.

I got the radio finished. The bcb oscillator coil was replaced with
a Meissner "universal" one. The other atnessna and Rf amp plate coils
were rewound. The set now works quite well.


Pictures are, in order, a view under the fidelity switch, after reworking.
Next is the finished bottom, then the front, tghen the top.

Very nice work.

That may be true, but sometimes it is good to be weird.

Today I recapped the TV power supply. Since I am not restuffing electrolytics,
just papers, this was easy. It worked correctly with no load.

But I noticed something odd in the CRT resistor chain: The lowest resistor
in the chain is shown on all schematics as 330K. Mine is 560K.
The schematic shows the CRT "screen" connected at the top of
of the 330K resistor, giving 250V. My power supply has
it attached 470K above the 560K resistor, or 1030K above ground.
All other resistors are as specified. This makes the voltage about 780,
which is what I measure. This is not original. Despite being
in crates, my chassis have clearly been well used an the PS has been
worked on a bit. The original connection was clearly just cut off.

What was going on?

There are four different schematics for the TRK12/120. You need to check them all and see which one your chassis' matches best. They can all be found in the RCA Red books.

Darryl

I have the original RCA manual and the Rider's.

The TV main chassis is for sure a TRK12 because it has no limiter tube.
It has no grid cap on tube 9, no connections to pins 3 and 4,
so it must be the version in Rider's that uses IF grid bias as contrast control.
There used to be connections to pins 1, 3, and 4, but no longer,
they were cut off.

Of course, I am going to use one of the radar tubes rather than a real
12AP4 so that may make a difference in the G2 CRT bias.

Steve McVoy: do you know if the 12LP4 also needs different grid bias,
or is it non-critical for test use?

Question: the video chassis has 2 multitap chassis mount resistors that work
like Candohms but are not. They are constructed differently and look more modern.

If their resistance is OK, is it reasonable to just leave them as-is?

If they show the proper resistance and aren't shorted to the chassis, keep them.

I need to know two things to proceed on this TV:

Are the black (or dark gray) black plastic lozenge shaped capacitors
(150 to 3300 pF) in the TRK12 paper or mica, that is, should I replace
them on preventative grounds? I have proper mica replacements.

Secondly, what pins are what on the replacement radar CRT I have?

I have all the caps except those, the .005 uF paper ones, and the
0.1 uF 300V one replaced. When those parts arrive, today or
Monday from Mouser, and I replace them, (about 40 .005 ones!) I
will be ready to try it without the CRT and HV.

I have replaced only one resistor, the 13k part of the pseudo-Candohm.
All others were only borderline 20% high or spot on ... nothing in between!
And very remarkably indeed, ALL resistors of the same value and type
were within +2% of each other!

I'll check the pins on the CRT when I get back to Ohio in a couple of weeks.

I wouldn't replace the low value caps unless they are bad.

I've completed recapping.

I removed the fuse from the CRT HV supply.

With no tubes except the B+ rectifier inserted I brought it
up on a Variac with a meter on the B+. It got up to
normal voltage with not fuss.

I then inserted all tubes except the horiz and vertical outputs.
Or rather, I tied to. It seems I ordered the tubes for a TRK-120
and I've got a TRK-12. I'm missing a 6F8G and a 6H6.
However both of these, despite what the specs say, are
being used as single diodes. They were temporarily bridged
with (hold nose) silicon.

Again bringing up on the Variac caused no fuss.

Did I mention I was feeding a signal in? I checked the oscillator
frequencies and they are set for modern channels 2-6 as a
rubber stamp on the chassis says. It was set to Ch. 2.

Checking the signal path with a scope showed that it was getting all the way
to the outputs (audio and video).
Fine tuning and contrast (actually grid bias on all IF stages) wore
as expected. The video waveform actually looks rather passable.
The sound sounds OK on 2000 ohm phones (remember that it has
no amplifier.)

Next I checked the sync separator chain and it works fine.
The horizontal osc works and the hold works but the pullin
range is rather small. Is this normal for TRK
12s?

No sweep was getting to the horizontal output grid (no tube, remember).
This was traced to a bad width pot. Turning it caused drive to appear,
and disappear, with loud pops from arcing inside it. I have a modern
one that should work if it can take 300 volts.

The vertical system worked correctly, but again with rather small pullin range.

The B+ for the 2nd sync separator is 7 volts [sic] as shown
on the schematic.

So much for today!