Ice Cream & Cake: National TV7M

[M3-SRT8]

Purchased on the bay. Cosmetically okay, but I think I'm going to refinish the cabinet.

The chassis is a piece of cake. Its in nice shape, all the tubes test fine, and it actually has horizontal sweep. I've already recapped it, save for 6 electrolytics, plus those two .005 5000V caps.

I'm rather impressed with this little 7 inch television. Nice build quality, and a very simple, serviceable little chassis.

Outside of the need to refinish the cabinet, which means decals, I shouldn't have much problem with it.

It came complete, with all the covers etc, but it didn't come with knobs. That may be a problem.

Anyways, I'm away from my camera and computer for a few days, but I will post pictures when I return. I like this TV.

Lee

[M3-SRT8]

Oops. My bad. It's TV7W.

W as in Mahogany.

[bandersen]

I think they went with "M" for the metal version and "W" for the wood. I'll be starting work on mine soon.

The logo decal is red and gold. Not sure it two color decals are and more difficult to have made.

[M3-SRT8]

I've done a recap, in the only caps left to be replaced are the 4 canned electrolytic caps, and the two .005 5kV tubulars.

the tv works, but does not have vertical deflection. I've tested c81 and it is shot. No surprises there.

I've ordered 6kV replacements from Justradios. I assume they will be much more durable then the old wax paper caps. I almost ordered the 15 kV caps, but I figured that was overkill.

[M3-SRT8]

I tested all those one Watt 1 mega ohm and above resistors on the back panel. They all seem to test 10 to 20 percent above spec. A few seen below spec.

How critical are they? Should I just replace them all with modern two-watt gray resistors?

[bandersen]

I suspect if they're all drifted up about the same, you'll be OK because the voltage divider ratios will be about the same.

Not seeing much in the 1+ watt megaohm value range at Mouser

The reason they used 1 watt is because they have a higher breakdown voltage than 1/2 watt resistors. They strung a bunch in series for the same reason.

Typical limit for 1/2 watt is 350, 1 watt 500 and 2 watt 750 volts.

[M3-SRT8]

I purchased from Just Radios a complete kit of 2 W resistors. Many are valued 1 meg and above.

I'm just curious as to whether I should shotgun all these one watt resistors, as they are 65 years old, and may not stand up.

[bandersen]

Good deal. I guess the mainstream distributors don't see much demand for the high valued resistors.

As for replacing them, I've yet to see one fail, but they get far off value, it will effect the image on the CRT.

[M3-SRT8]

Here's a few pics of the chassis. Before shots.

It's been recapped now, and I'm waiting on .005 6kV caps.

[Sandy G]

National was an "Old Line" mfgr of ham & SW radio goods, they knew their way around electronic stuff.

[M3-SRT8]

Yup. I'm pretty impressed with this little TV.

This version uses 12 volt vacuum tubes in the horizontal and vertical sweep and synch sections.

I have the cabinet clamped straight to try to eliminate warpage. That part of this TV I'm not so impressed with, as it has little reinforcements internally. Oh, well. I'm in no rush.

[M3-SRT8]

Here's a shot of the chassis circuitry. Note the transformer next to L33, the filter choke.

It doesn't appear in the Rider's manual. I wonder what it is?

[bandersen]

Mine has it too. I'm pretty sure it's the auto-transformer used for the 105-115 / 115-130 AC line range selector shown on the first page in Riders.

[M3-SRT8]

completely recapped it. Restored full vertical deflection. Now I'm going through all the brightness, contrast, etc. Controls. Cleaning all contacts, disassembling them when necessary.

[M3-SRT8]

The TV-7W is up and running nicely. Many thanks to kbmuri. As always, his help is invaluable.

I bypassed the tuner, running the dvd signal direct to audio & video for a nice, clean signal.

Pics later.