Sylvania 1-076 arrived!

[jeyurkon]

I was hoping to power the set up tomorrow. That won't happen now. While cleaning the controls I discovered that the Horizontal Center pot was bad. I opened it up hoping to repair it but it's beyond repair. It's a 140 ohm 2W wire-wound panel mount. 43-140CT by clarostat. The wire was blown in numerous spots. It must have seen a very high current to do that.

I think the closest I'm going to find is a 150 ohm 2 watt composition pot that I found at Newark. I'm going to go ahead and order that. If anyone should have something more appropriate they'd be willing to part with please let me know.

John

[Bill Cahill]

What about the selenium rectifiers?
They need replacing as well...
Bill Cahill

[jeyurkon]

Originally Posted by Bill Cahill

What about the selenium rectifiers?
They need replacing as well...
Bill Cahill

One of the dangers of posting progress; I was afraid someone would notice that.

The selenium rectifiers form a center-tapped full wave -125 VDC supply. There is a 39 ohm resistor in series with each rectifier. I believe they're there to limit in-rush current. They won't protect the transformer if the seleniums short.

The output of the supply is already fused. I intend to put a fuse in series with the 39 ohm resistors to protect the transformer.

On our original set we had to replace the seleniums once in its lifetime.

As long as the transformer is protected, I'm not worried. I have a lifetime supply of selenium rectifiers and if I have to change them every 5 years or so I don't have a problem with that. They're easy to get to and change.

I can't explain why I want to keep them in use anymore than I can explain why I want to watch a 60 year old TV. Maybe I just like the smell of garlic.

John

[jeyurkon]

Well, I'm glad I went the variac route. I did use the watt-miser. I used it on the primary of the variac so I was only able to monitor total power and not the voltage and current separately.

Things were coming up nicely. While letting it sit at 90 VAC smoke suddenly wafting up. A 100 ohm plate resistor on the 4th video IF stage was overheating. Since I was watching the bottom of the chassis when this happened it took me a bit to understand what was going on. One end of the resistor goes to +170V and the other connects to the IF transformer primary which connects to the plate of a 6AG5. When I measured the IF transformer side of the resistor it showed zero ohms to ground. I thought the IF was shorted. I pulled the 6AG5 and immediately saw what the problem was. It had gone up to air.

The pins on this tube had been severely bent at some point in its life. It tested good so I kept it, but there must have been a small crack in the glass. As it heated up it eventually cracked open.

Up until this point everything was fine and the voltages were coming up properly and nothing was overheating. The power consumption was still below spec.

I'll start again tomorrow. It's late now.

John

[jeyurkon]

I powered the TV up tonight. I checked out the FM receiver first and it sounds great! I need to make a loop antenna for the AM. It can't work without it. I tried anyway and all I heard was my neighbor's SSB transmission.

I then checked out the TV. I was surprised to get a raster let alone an image. I was very happy the the HV section was working because there were quite a few bad components that I had to replace.

I had to readjust the Horizontal frequency coil by about 15 turns to get it to get this close.

There is no audio on TV. But that's a pretty small section to look at so I don't expect it to be too difficult to fix.

Anyway, the image is below. All the major components are working so I should be able to fix the remaining problems.

Actually the main problem probably is that I wanted to try to keep the selenium rectifiers. They seem to test good, turning on at 6 volts and having zero reverse current at 100 volts. The low reverse current was pretty unusual.

They seemed fine until I plugged the HOT, VOT, and RF HV Osc tubes in. Then there was a 40 volt drop and the seleniums started to get warm. I was going to use NOS ones that I have, but they have a high reverse current.

As much as I like playing with old technology like selenium rectifiers, I'll have to give up on them.

Going to 1N4007's will bring the -90VDC up to -130VDC and may solve some of the apparent problems. That's not related to the sound though.

I may have to do a complete horizontal alignment since I replaced all the caps in that section.

I was very happy to see it do this much!

John