TUBE CROSS REF
TUBE INFORMATION SHEET
Tubes may be known by several correct model names, each depending upon where it was made and how it was meant to be used. The table of tubes below contains many of the common audio and radio frequency tubes used in vintage tube gear.
Many tubes were manufactured for third parties and carry the third party “Brand” name on the, but were actually manufactured by a different company. You can find “RCA” tubes made in a Sylvania factory and “GE” or “RCA” tubes manufactured in a Tung Sol plant. Confusing? – Yes!
So how do you know which company actually manufactured the tube you are holding? Most tubes have a Factory Code printd on them, and maybe an EIA (Electronic Industries Association) Code and these codes tell you the answer (many have rubbed off over the years so you have to be a good tube detective!)
Here are the most common factory codes found on many vintage tubes:
GE made many Admiral tubes.
Sylvania made many tubes with brands like: Fisher, Conn Organ, Magnavox, Crosley, Philco, Ford, Admiral, Motorola. Also famous for their “Chrome Top” tubes.
CBS Hytron was a high quality manufacturer but much smaller than the main tube manufacturers RCA, Sylvania and GE. They made tubes with the Motorola, Traveler, CBS-Hytron brands and many others.
The CBS Hytron construction is easy to identify: Clear Top design, Black Plates, the famous hole in the plastic key pin, getter shaped like a `square D`. Vintage is 1950s.
RCA was a large tube manufacturer and made tubes for brands like Magnavox, Emerson, and Motorola.
Tubes must be biased correctly to operate as designed. Some amplifier are self biasing in that they use a fixed bias or a cathode bias which is not adjustable. With these type of amps (like many 6BQ5/EL84 and 6V6 based amp), you may just replace the old tubes with new ones and forget about any bias changes.
Other amps have an adjustable bias potentiometer for fine tuning the bias settings. If you don’t have a bias measurement tool for setting the correct bias, leave the bias setting alone and just substitute the new tubes. If they begin to glow a cherry red, the bias is set incorrectly and will have to be adjusted (down or more negative) to get rid of the cherry glow on the plates. Usually a mid range setting will suffice, but if you do have a bias setting meter AND you know how to SAFELY set the bias then the setting s in the following table may be helpful if you do not have access to your amp manufacturer’s specifications. If you do not feel comfortable making this settings, by all means take the amp to a qualified amp tech.
Updated July 16, 2012
Copyright 2012 Tubemeister