Sound in the Video

9/5/2006 12:03:09 AMLou

Gentlemen:

I am working on a 1949 Hallicrafters TV (7 Inch Screen - Electrostatic Deflection).

I have two problems ...

1. I cannot seem to understand why I have sound modulation on the video. In this set the sound pickoff is after the video detector, and I cannot seem to find any sound traps in the schemtic. Pehaps someone can tell me where they are located and how they are adjusted.

2. I cannot vertically center the screen, and the horizontal and vertical centering pots are near the end of their ranges. Will the centering be affected by low high voltage? I only have 3.5 Kv where I should have 6 Kv, but since the centering is accomplished by resistance bridge off of the Hv, I though everything should work in proportion.

Thanks for any input - I have gotten to the point where I have nice video!!

Lou

9/5/2006 7:49:35 PMEdd

Can't research without a model or/and chassis number.

9/5/2006 11:49:58 PMLou

Thanks Edd

Thats a Hallicrafters model # NC-TV7, or TV7M

There were two versions - one with a transformer - powered power supply and the earlier version, which is what I have, which is a transformerless power supply. Hope this helps.

Thanks - Lou

:Can't research without a model or/and chassis number.

9/15/2006 1:19:46 PMDr T

:Lou: I serviced a number of these when they were new and recall that the video B+ is also tied to the SCREEN GRID of the audio output tube. There is a bypass cap connected from the screen grid of the audio output tube to ground. Replace this and keep you leads short. These sets were poorly designed and closely resembled the Crosley and Muntz sets of the same era. If your trouble presists - double check the alignment of the video IF's to make sure that the video and sound are indeed 4.5 MHz apart. Good luck.

Thanks Edd
:
:Thats a Hallicrafters model # NC-TV7, or TV7M
:
:There were two versions - one with a transformer - powered power supply and the earlier version, which is what I have, which is a transformerless power supply. Hope this helps.
:
:Thanks - Lou
:
::Can't research without a model or/and chassis number.

9/16/2006 2:20:44 AMLou

:Thanks for the valuable response. I knew it had something to do with coupling thru the B+ or B- since it only happens when you turn up the sound. There is only an audio driver and output stage and the only common thing with the video section is the plate voltage. Well, this is a tough restoration, but I am still going at it - thanks, Lou

:Lou: I serviced a number of these when they were new and recall that the video B+ is also tied to the SCREEN GRID of the audio output tube. There is a bypass cap connected from the screen grid of the audio output tube to ground. Replace this and keep you leads short. These sets were poorly designed and closely resembled the Crosley and Muntz sets of the same era. If your trouble presists - double check the alignment of the video IF's to make sure that the video and sound are indeed 4.5 MHz apart. Good luck.
:
:Thanks Edd
::
::Thats a Hallicrafters model # NC-TV7, or TV7M
::
::There were two versions - one with a transformer - powered power supply and the earlier version, which is what I have, which is a transformerless power supply. Hope this helps.
::
::Thanks - Lou
::
:::Can't research without a model or/and chassis number.