TRK12/120 Restoration

[Steve McVoy]

Doug, have you replaced the two HV capacitors in the 7500 v power supply? Checked the resistor between the capacitors? Checked the 7500v line while turning up the brightness?

Though the picture on our set get somewhat out of focus as you turn if you turn up the brightness too far it doesn't bloom.

[dtvmcdonald]

The HV does not collapse. Blooming is probably the wrong term.

It looks like space charge, curable only by higher anode voltage.
The tube I have can generate dangerously high brightness.

The resistor has been replaced, and both caps appear to be in good shape.
Their capacitance measures OK at low voltage, they do the job, and
don't get warm.

One question for somebody who has a very original one:

WHERE is the loose clip-on pilot light that comes
out of the radio power supply supposed to go, and do?

[Steve McVoy]

On the front, right below the bars over the speaker,on the 120 cabinet only.

The radar tube is much brighter than the original 12AP4 because of modern phosphors and aluminizing.

[dtvmcdonald]

Ah yes! There is the spot for the lamp.

But it does not work because the restorer had to completely
replace the front bottom piece of wood due to terminal rot
and of course had not been instructed about the lamp.

I will return to Plan A and construct a small mount to make a suitable
spot of light on the rug under the set.

[ChrisW6ATV]

Wow, very nice picture on your set!

[dtvmcdonald]

Additional pictures, made on a tripod.
The weather one has the high temps showing only one
field, so the scan lines show. The criss-cross pattern is
color dots. Pictures are grayscale.

[Electronic M]

The chroma info passing the IF so well makes me wonder if during the field sequential/early NTSC days if anyone ever added a color wheel to a pre-war set because it was handy and not valuable at the time....It would be darn cool to find a prewar set with such a vintage modification.

[dtvmcdonald]

One more question: My set does not have a back, and I don't really care to
install one, as it just heats this up (though these sets are very well ventilated).

But if I should find one: are the backs for the TRK-12 and TRK-120 different?
My cabinet is a TRK-120.

[tubesrule]

The backs on these sets are a completely open metal mesh on a small wood frame. They do not cause heating inside the cabinet. The back is the same for both versions.

Darryl

[dtvmcdonald]

Another note for TRK12 users:

While I did not notice it on program material, I noticed
a considerable (say 1/8 or 3/16 inch) bending of vertical lines,
moving at the usual 60 vs 59.94 Hz beat frequency. This could only be from
hum pickup from the heater power, or magnetic fields, since
it clearly was 60 Hz hum, not 120 Hz.

Installation of a cylinderical Mumetal shield on the
area between the socket of my radar tube and the yoke cured it,
so it was magnetic. This was a shield made for a
2 inch photomultiplier.

My experience has been that for these noncritical applications
a 1/16 or 1/8 inch wall plain steel tube , degaussed first,
would work fine.

[colorfixer]

Does the long persistence phosphor in the radar tube not mess with moving images?

[dtvmcdonald]

The CRT is one of those that had the phosphor replaced by a real year 2000 or so P4, is
aluminized, and has a new gun. Only the glass bell is from a radar tube.

[dtvmcdonald]

Originally Posted by Electronic M

The chroma info passing the IF so well makes me wonder if during the field sequential/early NTSC days if anyone ever added a color wheel to a pre-war set because it was handy and not valuable at the time....It would be darn cool to find a prewar set with such a vintage modification.

I didn't notice this comment before. I have no idea if anybody did that.
The actual picture resolution of the 9T246 you sold me is just as good.
However, the IF response, swept, is not quite as good as the TRK 12. As I
mentioned earlier, in the TRK12 it is stellar: in fact it actually, really, no quibble,
is as good as the CT-100, which is as good as any RF-based set
can be. Note that the IF of the TRK12 is 8-12 MHz or so.

And remember ... on screen, with a 441 line picture, the horizontal resolution
of the TRK-12 would be better than ANY true NTSC set.

[dtvmcdonald]

I'm restarting this thread.

I got a bee in my bonnet about my (this thread's) TRK-120 radio (its for sure a TRK-120 radio as it has no feedback switch nor eye tube).
The TV continues on it way as a I reported above.

Electrically the radio works perfectly. Mechanically the motor system also works perfectly and stops nicely. The push buttons have
proven somewhat dicey. The push buttons themselves were sticky and a big problem. In a two hour marathon I managed to
get them all off and reamed them out with a 1/8 inch end mill. This fixed that.
But the contacts on the push button bars are flaky and seem to require constant
attention with DeOxit. I suspect that the only cure for this is to take it apart and
gold plate everything heavily.

But that's not the major annoyance. The radio/amplifier works perfectly on TV shows
or voice-only radio programs. But on our two local AM music stations (which I need never actually listen to on it of course) it is abysmal. Its more abysmal at the
bassiest setting. It sounds like the speaker bottoms out. These stations DO have excessive low, very low, frequency bass. The radio has a built in bass boost at
low volumes that can easily be fixed if one wants nonoriginality. Is this a characteristic of the speaker mounted in an unclosed cabinet, or does it need
a rebuild job?

Also, the volume control has returned to scratchiness. Last summer I inquired
about a replacement and somebody said they had one. BUT ... would it be equally troublesome? Mine worked perfectly after removing the tin whiskers and using
DeOxit on it.

Should I punt and install a modern or st least late-40s/50s control?

[dtvmcdonald]

I spent hours yesterday playing with this thing (TRK120 radio).

Main problem is the speaker. It is original and works. All coils are working correctly. The cone was indeed rubbing and vibrating badly at low frequencies.
Its paper and hopelessly fragile. I tried shimming the cone in places with
squishy form to damp out the problems, this works OK but clearly will eventually fail due to cracking the paper.

There are places that recone old speakers. Has anybody else had one
of these speakers redone, or a similar one? It is a very garden variety late
30's 12 inch electrodynamic one with an attached push-pull output transformer and hum bucking coil. The frame is in first class shape. And suggestions about where to have it reconed?