Hi guys. I have three questions about tubes.

1. I have noticed a very small hole on most of the "G Type" shoulder tubes I am cleaning. Could anybody tell me more about it. Most all look machine made.

2. Did"G" tubes come out earlier the GT type, or are they the same. And what is the difference between both.

3. I also noticed a few of my older Philco "G type tubes" have two numbers after the PHILCO logo on the base, "07", and there are about five Philco tubes with that same numbering right after or before the PHILCO logo. What do those numbers mean, and how can you tell a matched pair.

I am trying to learn more about tube tech and different types. I have read up a bit on how the heater, plate, cathode, and grid function, neat stuff. Thanks for the help.

Jon

Not much help here, but the 'G' did come out first. Get Sibley's 'Tube Lore' for a lot of info on tubes. The numbers on the Philco are prob. date codes.

Gene

1. You'll need to say where the hole is.

2. Shouldered or more technically ST-bulb tubes were introduced in 1932. These are tuber like the type 57, 58, 75, 77, 78, 2A7, etc. The "G" suffix did not come into use until 1935. It was originally used to differentiate the glass versions of the original octal metal tubes. So, for example, the 6A8G is the shouldered, glass variant of the metal 6A8. The "GT" suffix came with the introduction of tubular T-9 bulbs IN ABOUT 1938 and is intended to help differentiate them from either the metal or "G" style counterparts. So, to follow the above example, the 6A8GT is a 6A8 in a T-9 bulb.

The "G" suffix is not a "technical" designation, but it implies a tube with a shouldered ST bulb and an octal base (the battery radio series of 1A5G, etc, and the 6AD6G and 6AF6G tuning eyes are the only exceptions). It would be improper to refer to a "6A7G", for example, since it does not have an octal base. People often make the mistake of referring to "6E5G" or "6G5G" tubes to refer to examples with shouldered bulbs, but this too is incorrect.

3. The letters and numbers are the date code. The scheme changed over time, but the tube you cite (the letter) "O" and "7" dates from the first quarter of 1937. Starting in about 1935, Philco date codes used the letters "OPUS" for the quarters, and the number is the last digit of the year. Ho tbranding (so called "engraved") changed to yellow printing in late 1937 or early 1938.

Your question on "matching" is unclear to me. If you are trying to create a date-matched set of tubes for a radio, you must take into account that a maker did not make all tubes at all times. So the date on tubes a radio came with could vary pretty widely. Of course, you must also take into account that one maker might not have made all of a particular brand. in the case of Philco, Sylvania was their largest supplier, but they got at least some tubes from Raytheon.