Pilot TV-37 Restoration

[dtvmcdonald]

Use .02 uF film or 6 kV ceramic caps for vertical deflection coupling,
or .05 uf 3kV ceramic ones. These, of course, will bite you much worse than
0.005 uF ones.

If you have the Rider's vertical circuit with the two 1500 pF bridged feedback caps, switch to the Sams circuit.

That fixed mine.

[jr_tech]

If you adjust the picture to about 1/2 the vertical height, is it still non-linear?

jr

[Crist Rigott]

Originally Posted by timmy

Wow, my big bad, lol, yes I already done it I looked back on my notes for when I restored it. It was such a small change other then the restoration it self so yes it's done and no lines ever since, lol.

I tired this and I ended up with more retrace lines! Any suggestions?

[Crist Rigott]

I'm going to stick with retrace line removal then concentrate on the V. linearity problem.

[jr_tech]

Originally Posted by Crist Rigott

I'm going to stick with retrace line removal then concentrate on the V. linearity problem.

If the vertical sweep is distorted, the blanking pulse derived from it may also be distorted. If it were my set, I would concentrate on getting the vertical correct first.
Just a thought, I did not need retrace blanking added to my set, so I don’t have first hand knowledge.

jr

[Crist Rigott]

Ok. I have another TV-37 here and it is wired like the Sams. so I rewired this TV37 to be like the other set and Sams.
Still no joy.

[timmy]

I agree fix whatever may be wrong with verticle first then do the retrace mod. My pilot had lines all over the screen but every one is gone after doing the mod.

[Crist Rigott]

OK. I'll work on the Vertical Linearity problem first.

[kvflyer]

Originally Posted by Crist Rigott

OK. I'll work on the Vertical Linearity problem first.

Excellent, good move! I suspect that you may find it quickly.

[Crist Rigott]

Well I tried switching tube positions and still no joy. I used my other CRT and tired it away from the speaker and that didn't help either.

[timmy]

Do you have the hv cover on while trying it, because if you don't then you will have a lot of distorted lines from hv leaking to the crt.

[Crist Rigott]

Originally Posted by timmy

Do you have the hv cover on while trying it, because if you don't then you will have a lot of distorted lines from hv leaking to the crt.

Yes, the HV cover is on and screwed to the chassis.

[dtvmcdonald]

I brightened up your linearity picture so I could see it well.

Its really bad. Mine started out bad, but not anywhere near that bad.

Something is seriously wrong with the generation of the signals.

First make sure that the HV for the CRT is up to snuff with a reliable HV probe.

Next make sure that the HV voltage divider resistors are correct and not partially
shorting to ground. Note that the linearity is dependant on what is somewhat like
a current source from the HV chain. Be sure that that 0.002 uf cap on the focus
center wiper is OK. You might add another one from the top of the focus pot to
ground. That picture looks a bit out of focus ... that's an important symptom!


Then get out the oscilloscope with a 10 meg
probe and start snooping around. The waveforms at the plates of the two
video output sections should be reasonably linear and also important,
approximately equal size. If not, make sure that the B+ and B- voltages are
reasonably what the table says and that the voltage divider for the second stage
grid is right. Try different tubes. Wholesale parts replacement may be in order.

But first, get the HV and focus chain exactly right!

[timmy]

With my pilot I had small issues because of low B+ so I added a diode to the rectifier tube and that fixed the low voltage along with the other problems. Is your hv at least 2-2.5 kv ?

[dtvmcdonald]

I was working on my Pilot yesterday to see why it always showed hum in the picture
and the horizontal sync broke up if the contrast was too high. It has always done this.
It turned out to be my mistake .. a 6BA6 with a very mild case of heater-cathode leakage
was in the last IF amp socket and a good 6AU6 was in the video amp socket. That's
backwards. Moving the 6AU6 and a new 6BA6 almost fixed that. The remaining hum
is probably capacitave from the series heater string.

I also needed to tweek the audio IF trap so I looked under the chassis.
My set, which has good linearity, is using two .02 uF 6 kV ceramic caps in parallel
for each vertical deflection plate coupling.