Ice Cream & Cake: National TV7M

[DavGoodlin]

Originally Posted by M3-SRT8

completely recapped it. Restored full vertical deflection. No I'm going through all the brightness, contrast, etc. Controls. Cleaning all contacts, disassembling them when necessary.

Those Nationals look about the most like lab test equipment when it comes to how they're put together. Very nice stuff - like to see the operating pics

[M3-SRT8]

Here's the chassis, finished and working. "The Music Man" (1962)

[ChrisW6ATV]

Very nice work, Lee.

[M3-SRT8]

A semi-final restoration note:

I had not replaced the selenium rectifier with a diode. So, I went down to the local Radio Shack to find a 1N-4007 (1000V 3 amp) but all I could find was a 1N-4005 (600V 1amp).

Installed it anyways, and noticed the HV is now over 3KV, the screen is brighter and clearer, and the Audio screams loud and clear with no distortion.

I figure the 1N-4005 might be still choking off the HV (should be over 4KV), so I will replace it with a proper 1N-4007 when I get one.

Replacement electronic parts on Martha's Vineyard ain't all it's cranked up to be.

[Sandy G]

I'm thinkin' that Bad Boi was made not too far away in Malden, Mass...

[M3-SRT8]

You are correct, BD. Malden, Mass.

I'm betting once I put the correct diode in this TV will finally be uncorked.

[M3-SRT8]

What do you watch on a 1948 National TV 7w?

Why, Humphrey Bogart, of course. In the Treasure of the Sierra Madre.

[Kevin Kuehn]

Originally Posted by M3-SRT8

I'm betting once I put the correct diode in this TV will finally be uncorked.

Hmm. I'm thinking all silicon diodes have basically the same forward voltage drop. Their voltage rating(peak inverse voltage)is the max reverse voltage they can block without breaking down (self destructing). So I don't believed changing from a 1N4005 to 1N4007 is going to give you any higher output voltages. The 1N4007's higher PIV will give the diode's a higher margin of safe operation.

Nice job on the restoration. Nice sharp picture.

[M3-SRT8]

Originally Posted by Kevin Kuehn

Hmm. I'm thinking all silicon diodes have basically the same forward voltage drop. Their voltage rating(peak inverse voltage)is the max reverse voltage they can block without breaking down (self destructing). So I don't believed changing from a 1N4005 to 1N4007 is going to give you any higher output voltages. The 1N4007's higher PIV will give the diode's a higher margin of safe operation.

Nice job on the restoration. Nice sharp picture.

Thank you. I've been running it for 3 days now, about 4 hours constant usage in one setting. The only nits to pick is an occasional sonic crackle, or a rare horizontal tic. But 99.5% of the time she is a rock-solid performer. In a room with moderate light the picture quality is very good. Great in the dark.

The sound quality is superb.Even out of the cabinet it has decent bass. Mid and treble is excellent. All told, this is one impressive 7" television.

If the diode (rated 1 amp) isn't holding it back, I wonder what is causing the lack of hv.I've replaced all caps, and I mean ALL caps, in the hv, horizontal, and vertical sections, along with all resistors that were off by more than 10%. All the resistors at 1 meg and above are replaced.

It also has a slight vertical linearity issue. I figure this is also due to the lack of peak hv. I get only 3.5 kv at a test point that should yield 4.5.

I have tuned the mica in the hv cage for peak voltage.

[M3-SRT8]

All the bleeder resistors and all the resistors under the hv cage were replaced.

[Kevin Kuehn]

Not sure about your low high voltage. 1N4005 and 1N4007 are both rated for 1 amp current.

[M3-SRT8]

Originally Posted by Kevin Kuehn

Not sure about your low high voltage. 1N4005 and 1N4007 are both rated for 1 amp current.

My error. I thought 4007s were 3 amp rated. Then the diode clearly is not the bottleneck.

[M3-SRT8]

Soooo...that leaves the flyback. I already cleaned it with alcohol and blew dried it with a heat gun to chase away any dust, moisture, etc.

I've read these pages on electrostatic 7" tvs...

[M3-SRT8]

Alright. Guess tonight's movie...

[batterymaker]

Flight of the Phoenix?