Back to the VT-71H

[Yamamaya42]

Originally Posted by dtvmcdonald

There are other tests you can do! First, get a .01 to .047 uF film cap (greater than 250 volts) and connect the 6.3 volt filament line to pin 2 of the CRT (point C on Sam's) with it. This should generate a substantial hum bar on the screen.

You could also try connecting the 6.3v through that cap to pin 1 of V6 (video amp) as that should product a really strong hum bar.

enter confused mode---

The heaters are series wired in this set, so which point in it would be a tie reference to give the 6.3v for a hum bar pattern to show on the screen?

[Chris K]

Originally Posted by bandersen

Ground for the composite source connects directly to B-. Anything 0.01 and up for the connection between the composite signal and tube grid as Yamamaya42 said.

So what I'm thinking is that the 6AU6 plate is being shorted to something and the screen is acting as the plate to get a signal for the audio. What voltage do you have on the plate and screen (pins 5 and 6)? How about the 6.8K, 4.7K resistors and 20uF cap?

Good luck!

Jesus...I have -0.5V on the plate and 180V on the screen. 180V through the whole circuit all the way to the 20uf electrolytic. I'm grounded to B-

[Chris K]

250V going into the detector and nothing coming out

[Chris K]

First IF amp, 6AG5, I have no voltage on pins 1 and 2...around 100V on 5 and 6.

[Yamamaya42]

so, now you have a fault to track down! Congratulations!

[Yamamaya42]

Originally Posted by Chris K

First IF amp, 6AG5, I have no voltage on pins 1 and 2...around 100V on 5 and 6.

this seems normal

[bandersen]

Like I keep suggesting - do the resistance checks. Should be around 11.5K between pin 6 of the video amp tube and B++ (pin 4 of the ballast tube).

https://www.earlytelevision.org/pdf/..._sams_83-6.pdf

[Zenith26kc20]

Looking at the schematic, the 20mfd electrolytic that goes to the screen grid on the 6AU6 only has three parts that bring plate voltage to the 6AU6. A 6800 ohm resistor, and two coils. I would bet the 6800 is good as on my set it is a two watt. The small coils could have some corrosion where they connect to the leads. Looks like they are wound on resistors.

[Chris K]

Timmy has the VT71 but he has questions as to the chassis designation. It does say TS-4H on the chassis but it's hand written. I've looked at a couple of sites for manufacture date and serial number (including VK), and I think it's a TS-4H but I'm wondering if there are sources in this community who could venture a guess. The chassis was manufactured in June 1948 with a SN#38069. Oh and BTW, I think my work is giving Timmy angina!!!!! Thanks all.

[timmy]

Is there a way to differentiate between the ts 4j 4h 4d they all use the same ballast but there are slight changes between them is there any concrete tell tale that would identify any differences.

[timmy]

Hey Chris I believe I found the voltage and resistance chart

[Chris K]

Great Tim!!! Thanks for trying to undo my mess!!!

[bandersen]

Serial # 38069 would be TS-4H. The TS-4H does not use the same ballast as the TS-4J late. It uses the older '303 type

[timmy]

Originally Posted by bandersen

Serial # 38069 would be TS-4H. The TS-4H does not use the same ballast as the TS-4J late. It uses the older '303 type

Really wow I have 4h 4j and 4d schematics and from what I see it shows r80 for all 3 look the same. Ok great now we know that this set is infact a 4h thanks bob for that info. The 3 ballasts seem to show the same resistances but I think the ts-18 is different with one less resistor.

[timmy]

Hey Chris the ballast you made is that design for this ts-4h ?