DuMont model# RA-166

[Tom9589]

I just looked at the schematic. The brightness control varies the voltage at the control grid of the CRT, not the cathode as in many other sets. As Notimetolooz said, check the brightness circuit. If the 330K resistor going to ground is open or grossly increased in value, that could make the brightness very bright.

One question to ask. Can you adjust the brightness so that the screen goes dark?

It also looks like the path between the plate of the video output tube to the CRT is DC coupled. Check that circuit as well as it could be throwing the DC bias off at the cathode of the CRT. There are also a lot of inductors in that circuit. A simple resistance check could find out if one of them has opened up.

[cademan]

I can adjust the brightness just fine. What you see is about half way up. It does go completely dark. The camera may show it as overly bright but it is at normal brightness.

My problem is not getting any signal. It is operating just like a straight monitor without a tuner except when I bypass the tuner and inject a signal, I still get nothing.

I checked the inductors and none are open.

This one has me scratching my head. I sure wish I had the proper testing equipment.

[Yamamaya42]

Well, the schematic says that the ptp level going into the final video amp p2 (12by7) is 3v, and composite is only 1v, but you should see SOMETHING, even though you are feeding in low amplitude there, also, it's best to remove the det tube 12au7 when you feed in video at the test point p2 (12by7) , so it's not loaded down, & if you have an o-scope, you should see some kind if inverted video on the cathode of the CRT, as indicated on the schematic.

[Tom9589]

How are the voltages on the CRT? In particular, is the voltage at the cathode low?

[cademan]

Voltages at the CRT are spot on.

[Notimetolooz]

Check for a video signal at pin 7 of the video detector tube 6AL5 with your scope while feeding a RF signal into the tuner adjusted to that station.
If you find it there check for it at the testpoint on the grid of the video amp 12BH7 pin 2.
If you find it there look for it on the CRT cathode pin 11.
I assume you tried varying the contrast control.
If you can't find a video signal at the video detector then try injecting a signal using a DC blocking cap (0.1 uf) of a 1-3Vpp signal at the plate (pin 7) of the video detector tube. This signal could be from a audio generator. ( I think someone suggested that before.) You should see something other than a blank screen.

[Yamamaya42]

Originally Posted by Notimetolooz

Check for a video signal at pin 7 of the video detector tube 6AL5 with your scope while feeding a RF signal into the tuner adjusted to that station.
If you find it there check for it at the testpoint on the grid of the video amp 12BH7 pin 2.
If you find it there look for it on the CRT cathode pin 11.
I assume you tried varying the contrast control.
If you can't find a video signal at the video detector then try injecting a signal using a DC blocking cap (0.1 uf) of a 1-3Vpp signal at the plate (pin 7) of the video detector tube. This signal could be from a audio generator. ( I think someone suggested that before.) You should see something other than a blank screen.

OK, now you have me very confused...
Are we looking at different schematics? I'm looking at http://www.mcmlv.org/Archive/TV/Dumont_RA166-171.pdf
which has the detector as a 12AU7, and the amp as 12BY7, but you mention, 12BH7, which schematic are you looking at? Do I have the wrong one?

[cademan]

My chassis uses the 12BY7.

I haven't been out to work on it for a day or two but I will probably be checking it out later tonight or tomorrow.

My schematic is out on my computer in my pole barn where the tv is. I am currently inside the main house on a tablet and don't have it saved to it. There is a difference in 6AL5's used but I will have to go and take a look again.

[Tom9589]

Yamamaya42, please look on page 27 of the schematic you referenced. This DuMont did use a 6AL5 on some runs and a 12AU7 on other runs. Likewise, it used a 12BH7 on some runs and a 12BY7 on other runs.

[Notimetolooz]

Beitmans 1953 Volume TV-7, page 42.
Might be a different version (RUN). The tubes (and pins) might be different but the functions are the same.
https://worldradiohistory.com/Beitman-Manual.htm

[cademan]

OK, some progress. I got a picture using my old vcr but it needs some serious adjustments and after 15 minutes of being on, I lost my sound. Now what's that all about.......damnit!

[cademan]

Update: I need 11 more new capacitors and am just waiting for delivery. As it stands now, I get a picture but the sound fades out after about 10 minutes. After I get all the rest of the capacitors replaced, it will be totally recapped.

I will then go through and clean all tube sockets and tuner. All the resistors check out fine. It will probably be a good tv once I get it all tuned up.

Thanks for any and all info.

[cademan]

New update: Got a real good picture on it now that everything inside is brand new. Still have a sound problem but I'll get that worked out later. Right now I am happy that it has a good clean bright full clear picture. I will post a pic later on. Thanx for all who replied. It was helpful.

[cademan]

For those that may still be watching this thread:

Here's pics. Still don't have sound (yet) but at least the damn thing is working!

[zenith2134]

Very nice pix, have you addressed the audio issue yet? Hard part's done! Your video looks clean which obviously eliminates many upstream signal issues. Sounds to me like there could be something simple such as a break in one of the solder connections. Is the audio output tx okay? Signal past sound IF?