My Christmas day 9T246 restoration! Almost.....

[wa2ise]

Originally Posted by ChrisW6ATV

Are you confident that the original part you took out was a .039? Photofact schematics are not infallible, as I am sure you know. Were other adjustments or replacements made in the horizontal oscillator or output circuits, while the .01 was in place?

Sam's errors, or it could be a production change at the factory that wasn't documented. Or maybe, as mentioned above, a similar but not identical replacement part was used, and that required a different cap be used to make it work. Maybe the factory ran out of the "correct" part, and made a substitution, so they could get sets built and make the production schedule, and get sets shipped out the door.

[Kamakiri]

Actually, here's what happened.

Rather than read the value of the bumblebee that was on there, I went by the schematic. Schematic said it was a .01, so I put in a .01. Then, I find out that I had the wrong schematic, and the value should have been .018. It worked fine with the .01, but for accuracy's sake, I replaced it with a .018.

Turned on the set. Back to square one. Decided to go back to the .01. BAM. Dead on. One of those God moments, I guess

Incidentally, put another hour of runtime on it yesterday watching Family Guy and Big Bang Theory. If anything would have caused the set to overload, that woulda done it

[Kamakiri]

Originally Posted by ChrisW6ATV

Photofact schematics are not infallible, as I am sure you know.

Ahhhh.....no, actually. I didn't know that....but I sure do now.

This set was good prep for me, because I start the DeWald in a couple weeks

[Bill Cahill]

congradulations on a job well done, Tim. As you can see, there were also changes over the life of these sets.
Bill Cahill

[Kamakiri]

After just over 30 hours of play, I decided to yank the chassis and test the tubes. Replaced a weak 6J6 oscillator.

Still makes a great picture, and very stable. Have had no issues with the set

[dtvmcdonald]

I'm going to hijack this thread, since my "new" 9t246 from the 2013 ETF convention
has a similar problem. This set was recapped and had several resistors replaced
by the previous owner. It basically works perfectly except for horizontal linearity,
which is abysmal. The previous owner had replaced R106 (10k) with 6.8k paralleled
with a rather large capacitor (value unknown since it was several smaller ones
paralled, values hidden in the pile). This kludge made the linearity better but
still poor. I put back in the 10k and it works, bad linearity. He also reported that he
horizontal linearity coil (I presume he meant L42) got hot. It sure appears to me that
it is not getting hot.

Presumably the first thing to do is to take a proper scope home and adjust the
waveform per Sams. Now the questions:

1) Is there a source for the proper waveforms at many places in the circuit?
(E.g. the original RCA schematic and alignments instructions.) I didn't
find one on the net.

2) Since he said the (linearity) coil got hot, maybe it had a short ... are there new ones out there, or at least experience on a proper value replacement. It looks like lots
of turns in one big solenoid. Of course maybe horizontal oscillator alignment will help
things.

3) I seem to remember reading on another forum that the two capacitors C90 and
C91 on the horizontal coil were, on some sets, not the .033 and .05 shown on Sams.
Does anybody know anything about this possibility?

4) On another subject, the input circuit to the tuner seems bizarre. L2 looks like
a balun transformer ... but its not a balun circuit. The input side, presumably 300 ohms, is not balanced, as one side is grounded? What's the idea? I'm feeding it from
either a cable box or a DVD feeding through a VCR as modulator, coax through a good balun. I get fairly large signal increase and an absolutely huge drop in impulse noise
if I ground the shield of the coax to the set chassis. I tried feeding the tuner not
through L2 but direct with 75 ohms and it worked great.

4) The set probably does not have alignment problems, and I don't have
a signal generator, so I probably won't align it. But I had an idea ... I DO have
a good spectrum analyzer. Could I feed Comcast, which has QAM on just about
every channel, flat as a pancake from 54 MHz up to 700, as a signal source and
at least check alignment with a scope probe on the spectrum analyzer? Has anybody
tried this (with AGC set so it doesn't overload.)

Other than these comments, after setting the AGC right it gives an excellent
picture of eggs lying horizontally, or plain TV shows.

Any comments very welcome.

Doug McDonald

[Kamakiri]

Well, the set finally quit on me.

Turns out the issue was simple.....the picture tube was toast. I got about, oh, 60 hours of use out of that 10BP4 that was in there. The one I replaced it with, I yanked out of a locomotive that is probably best suited to parts. The tube tests pretty decently, but the picture on this set isn't as blindingly bright as the Crosley 630 clone I worked on months back.

I checked the HV to the anode (thanks to jstout for sending me that HV probe which I use ALL the time ), and I'm at 6 kV. Is that right for this chassis? Seems low to me.

[bandersen]

A 10BP4 typically runs at 9kV, 6 is definitely too low.

[Kamakiri]

Thought so. But I would think that if it was THAT much lower than spec, it wouldn't produce a picture at all.

[bandersen]

It would. I recently went through a battle with low HV in a 630TS. I was getting a visible raster down around 4-5 kV as I recall. It's much brighter and sharper at 9 for sure.

[Kamakiri]

So that said, where should I begin as far as a suspect component? Assuming total recap, good tubes, blah blah blah?

[bandersen]

Adjusting the horizontal drive control should have an effect on the HV. Also, there's usually a 1Meg resistor on the HV socket in series with the HV lead to the CRT that may be bad.

[John Folsom]

Try replacing the 1B3.

[Kamakiri]

The horizontal drive control seemed to have little effect. It seems just a tad brighter, but it's in the case now, so I couldn't test for HV. Gonna pull the chassis again, and go over it, as well as that resistor.

I tested the 1B3, and it was good, but I've heard that doesn't necessarily mean anything. It's an OEM tube (I think) with the "RCA Victor" script on it.....and I have plenty of NOS ones, so I'll dunk a new one in as well.

Incidentally, the set got some press today on Facebook

https://www.facebook.com/photo.php?f...type=3&theater