Back to the VT-71H

[Chris K]

Originally Posted by Yamamaya42

If you ever get back into working on the set, you always have the option of trying to direct feed video into the grid of the 6AU6, far side of point D on the SAMS, making very sure your video source is protected and isolated, ( TV on isolation transformer, video coupled via capacitor), according to the service manual, signal level out of video detector is 1.8v PtP, standard composite video level should be close enough to this to see SOMETHING W/O any amplification.

Thank you so much...yes I will try that. At the least, it will give me a reference as to what can be ruled out. Also, it will be so wonderful to see an actual picture on this!!! A few questions...what value capacitor...should the ground for the composite input be to the chassis or B- and, I have the variac set to 117 volts plugged into the isolation transformer so the setup is IT-Variac-Television. Is that OK? I know it makes sense to me but I trip over so much stuff in this hobby.

[bandersen]

Originally Posted by Chris K

Thank you so much...yes I will try that. At the least, it will give me a reference as to what can be ruled out. Also, it will be so wonderful to see an actual picture on this!!! A few questions...what value capacitor...should the ground for the composite input be to the chassis or B- and, I have the variac set to 117 volts plugged into the isolation transformer so the setup is IT-Variac-Television. Is that OK? I know it makes sense to me but I trip over so much stuff in this hobby.

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!

[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!

Thanks Bob and I will check those values and post later tonight. Do you want to know voltage on the resistors? They have been replaced already with 5% value resistors. I did that after I started troubleshooting issues from the video amp to the CRT, and the originals were spot on anyway. Timmy has graciously offered to get it going and we've worked out a shipping scenario but I'm willing to give it one more shot before bubble wrap, Styrofoam and a corrugated box!

[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-