Sylvania 1-076 arrived!

[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