117Z6G

According to the September-October 1940 issue of Sylvania News, see page 18 here , the center tap of the heater was removed from those tubes of later production, as UL considered it a safety risk. For replacement purposes in the seldom cases where the center tap was needed, the variant 117Z6GC was introduced.

The socket diagrams at the tube page show both versions with and without center tap, without comments so far.

I downloaded and read the article.

I'm curious.

1. Why would parallel operation at 58.5V ever be wanted?

2. Why did "Fire Underwriters" (UL?) rule the centre tap was not permissible?

"The cathode of ONE diode is connected to heater pin 7 - (half half indirect)"

How does that work on a direct AC mains set? It's not shown in the base diagram.

I've only encountered the 117Z3