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 Post subject: Re: Dumont Manchu rebuid
PostPosted: May Fri 17, 2019 4:31 pm 
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Joined: Feb Tue 26, 2019 2:11 am
Posts: 32
Interesting about the aspect ratio used in by modern broadcasters. Didn't know anything about it until now. Modern broadcasters probably think that the older TV's with the legacy 4 x 3 aspect ratio's are in a landfill by now.
The cable dig/analog converter I'm using is a Viewtv AT163.
I'm rewiring parts of the HV sub chassis. Primarily to measure the cathode current to the 6BG6. Unfortunately some of the cloth wiring is very rotten and needs to be replaced. Luckily the main chassis doesn't seem to have this problem. I did find however that the cathode resister (2 watt 47 ohm 10%, measured at 59 ohms ) and some change, while moving the wiring off the cathode terminal of the 6BG6. Replaced this and tested the HV sub chassis and all was ok. Today I will measure the cathode current to that 6BG6. The set also has a intermittent problem where the picture slightly jumps every 10 or so seconds accompanying a pop in the sound. Could be a bad tube? HV discharge? We will see.
The picture also needs to be aligned. Was able to pick up a DVD test pattern disk, and will align this set and the optics in my Philco 48-2500. Lofty goals here.
My goal is the replace the picture tube with the new old stock tube I picked up from Moyer electronics. By next week if all goes well the picture tube transplant should be completed.


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 Post subject: Re: Dumont Manchu rebuid
PostPosted: May Fri 17, 2019 5:20 pm 
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Joined: Mar Sun 01, 2009 10:27 pm
Posts: 4971
Location: Ann Arbor, MI
If you have a cathode resistor, you can measure the current without breaking the connection to the cathode. Just measure the voltage across the cathode resistor. The current is the voltage divided by the value of the resistor.

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Tom


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 Post subject: Re: Dumont Manchu rebuid
PostPosted: May Sun 19, 2019 10:37 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1461
Location: Phoenix, Arizona
Digital TV is 16 X 9 aspect ratio. Some sub-channels still do 4X3 with no video in the side bars.

Movies are 2 X 1 which is why some streaming movies get cropped by your new HD TV.

Set top boxes usually do some form of stretch or squish (zoom) depending on the brand. 14 X 9 was popular.

There is a data flag in the PID's called AFD (automatic Format Descriptor) Some set top boxes won't let you change the aspect ratio depending on what the program has encoded.

I have two of the 40 dollar coupon set top boxes and both have bad audio.

Jim


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 Post subject: Re: Dumont Manchu rebuid
PostPosted: May Wed 22, 2019 3:01 am 
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Joined: Apr Mon 16, 2012 5:31 am
Posts: 137
jimmc wrote:
Digital TV is 16 X 9 aspect ratio. Some sub-channels still do 4X3 with no video in the side bars.

Movies are 2 X 1 which is why some streaming movies get cropped by your new HD TV.

Set top boxes usually do some form of stretch or squish (zoom) depending on the brand. 14 X 9 was popular.

There is a data flag in the PID's called AFD (automatic Format Descriptor) Some set top boxes won't let you change the aspect ratio depending on what the program has encoded.

I have two of the 40 dollar coupon set top boxes and both have bad audio.

Jim


Just to point out...

525 line DTV can be 4x3 or 16x9. The broadcaster sets a flag at the emission MPEG2 encoder to signal to the receiver the format. The OTA set top boxes we use with our old sets should be set to 4x3.

AFD (Active Format Descriptor) is used only when the display format flagged by the encoder differs from the set top box format setting. Essentially AFD will letterbox 16x9 in a 4x3 display and endure full frame for 4x3 content.

The problem is that some local broadcasters screw it up and either the flag or AFD or both is incorrectly set!


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 Post subject: Re: Dumont Manchu rebuid
PostPosted: Jun Sat 01, 2019 2:34 am 
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Joined: Jul Wed 19, 2017 5:15 pm
Posts: 43
Have you thought about ditching the 19AP4 and using a 20CP4/20DP4? Should not need any electronic changes. Will need to find a way to mount it in the cabinet.


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 Post subject: Re: Dumont Manchu rebuid
PostPosted: Jun Mon 03, 2019 4:53 pm 
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Joined: Feb Tue 26, 2019 2:11 am
Posts: 32
When I got this set the 19 inch tube was already retrofitted by a local Dumont dealer. Unfortunately all the old mounting hardware for the 20 inch tube was long gone. It would be tricky and difficult install the 20 inch tube into this set, but not impossible. After warm up (15 minutes) the screen fills out nicely with the new 19 inch picture tube. I was able to find a new old stock Sylvania 19 inch tube and after installing it, the picture is sharp and much brighter than the original tube. With a little tweaking of the cathode on the horizontal output and a small shunt cap on the damper I was able to fill out the screen adequately.
I'm working on the Webster 256 two speed turntable now (which is in this Manchu entertainment console) and need a cartridge rebuild. This is a Webster Racine cart. which pivots vertically inside the tone arm engaging either the 331/3 or 78 needles after moving a lever on the arm. West tech will not rebuild this cart (which is dead) so I have already installed a 1977 astatic cart in it's place. It sounds great but the arm lever that changes the needles cannot work . I was amazed that the two idler wheels were in perfect condition and didn't need to be replaced, no flat spots and the rubber was still in great shape. The rubber motor mounts needed to be replaced which was no trouble.
Ill be posting some pictures after cleaning and polishing the cabinet. I don't have room for this set and will probably put it up for sale in the near future. It's been fun !


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