Garod 15TZ6 adventure

[bandersen]

Major TV recapping is done.


I now have full raster.


Tried feeding a signal into the antenna terminals but got no reception at all.
Next, directly fed a composite signal directly into the video amp grid. That got me a nice, clear image.


Some issues on the right side. Have not tried adjusting the hor. drive yet.


First, I'll work my way through the IF with signal injection.

I really hope it's not an issue with the unusual variable capacitor tuner.

[bandersen]

Signal injection to the rescue! Used a B&K 1077B to isolate the problem to the 3rd IF stage.
After checking resistors, coils, voltages, etc, I rechecked the tubes. The 6BA6 at this stage had 0 emissions, no filament glow and got very hot in my tester. Must have lost its vacuum. That's a shame as it was an industrial, long-life version.
This is one I had already replaced after my first round of testing.

I replaced it with a tube from my stash, but no improvement. I rechecked the replacement tube and it was bad too!
So, replaced it yet again with a NOS RCA, bingo! We have reception and sound!



I can also now see that the yoke is on wrong as the image is upside down and backwards. Wide bars should be on the left.


That means the horizontal scanning issue is actually on the flyback side, not the drive side.


I'll work on that next.

[bandersen]

Here's some actual video. The contrast control has very little effect and is much too harsh. It appears to work by varying the grid bias on the RF front end only.
I'm thinking it might also be an issue with DC restoration or brightness circuit.


Otherwise, it's actually working quite well. There is very good definition and i can easily make out small text in commercials.

[bandersen]

I missed a 100uF cap on one leg of the contrast control. After replacing that, the contrast control works as one would expect. At minimum gain, the image fades away, max gain and it's too harsh.

[bandersen]

Swapped out the HOT and adjusted, drive, width and linearity. Better, but needs improvement. I'll hold off on that until I get a proper round CRT with the right deflection angle.

[Tube TV]

Wow that was a nice score for free. It reminds me so much of a Dumont. Excellent work Bob

[bandersen]

Thanks. Maybe a passing resemblance, but it's quite a different design than a Dumont.

[bandersen]

I dug up a used 16DP4 CRT to try out tonight.


First without a focus coil just to see if I could get something.


Promising, so I slid the focus coil on the neck and spent a little time adjusting it, the ion trap magnet and yoke.
Better.


Yes, this will work. Hoping to use a similar 16LP4 which has the right deflection angle eventually.

[kvflyer]

Bob, I have to say that it doesn't get much better than that! Good on 'ya.

[bandersen]

Pulled the record player out of the cabinet and gave it a closer look.
It's absolutely filthy just like the other chassis.


It's a Webster model 256-2 than plays both 78 and 33 rpm.
Curious that there is a relatively modern blue plastic crimp connector.


It's actually bronze color under that filth.

[Electronic M]

Those changers revive fairly easy. The one in my Dumont manchu just needed the idlers, capstan and inner platter lip cleaned with Goof Off, a new pickup cart and some oiling.

[bandersen]

Ah, that's better. Motor is good, idler wheels and motor mounts need replacing.

[bandersen]

A friend with far more experience than I with record players stopped by today. It took most of the day, but in the end he did get it playing!
* Motor mounts have been replaced
* Changer mechanism lubed and working
* Crystal cartridge replaced with a modern ceramic one.
* Idler wheel has a dent but grips OK - I will look into replacing it


While he was working on that, I took another whack at the 15AP4 CRT.
I went through all the various restore/rejuv modes in the CR70 "beam builder" with no results.
I was about to give up when I gave the Manual restore 2 mode (the most aggressive) one last try.
This time I finally got a flash in the gun!
Emissions finally appeared but weak. Also the grid shorts test is borderline.


If I crank the filament juice from 6.3 to 8 volts, the emissions are also borderline.


So, let's give it a try.


Eventually I found the ion trap magnet sweet spot and got an image.
Brightness and contrast have to be set low on the image goes all weird. Sort of washed out and inverted.


I installed a brighteener and it improved a bit.
Other issues continue to crop up though. Keep in mind the image should fill the entire screen as this is a porthole set.
It is also sporatic. We had a decent image that just about filled the screen. Turned the set off and back on and now it's like this.
Stretched on left and compressed on the right.
I'll go back to the small test CRT while I troubleshoot the sweep circuits.

[ChrisW6ATV]

Originally Posted by bandersen

the image goes all weird. Sort of washed out and inverted.

That is one of the basic/common symptoms that identifies a weak CRT, but you probably already know that very well. I think you "did your best", now hold it for the day when you can get it rebuilt. It is certainly worth it.

The record changer looks great!

[bandersen]

Thanks. I plan to poke around with the rebuilding equipment at the ETF in the spring. At least to get more familiar with the steps involved. Who knows - I just may attempt to rebuild it myself someday.