[Don Lind]

Philco TV engineering worked from a list of approved or preferred tubes. It was based on what Lansdale could provide in production quantities and second sourced as well. Engineering had no way of knowing what tubes were laying around, nor did it care. Tubes were shipped somewhere as soon as they were made so few were laying around to be used in product designs that started two or three years earlier. Every tube had to undergo extensive evaluation and documentation so it was often more expedient to use one from the list than to undertake a crusade. New products had to get to the market on time.

Designs were frozen before production material was procured, not the other way around. Tube line up was determined by engineering, not purchasing.

Often old circuit designs and associated tubes were used because of an engineer's personal preference or proven reliability. That's not always a bad thing. A review of the year to year service information will show some circuits carried over for several years with few changes. Typically, the top line would incorporate the newest components and designs. Next year, that design would move down a tier and something new would move in on top. Cost improvement was on going.

Loctal tubes were more reliable and lower cost than their octal equivalents because there was no plug. The pins that extended through the glass plugged directly into the chassis socket, like 7 and 9 pin miniatures, eliminating the need for the additional plug and solder connections. This design allowed loctals like the 7F8 to work at higher frequencies. You will not find many octals working at channel 13.

Your project TV looks great.

Don