[Introduction] [capacitors] [Resistors] [Tubes]
Tubes
Most tubes are readily identifiable because the housing is a glass tube! Some tubes have metal instead of glass. The vast majority of glass tubes found in music amps come in one of several basic types:Metal tubes are similar to octal glass tubes, except that the tube is made of metal instead of glass. Some metal tubes have a connection from a pin to the metal shell, meant for grounding. Using a metal version of a glass tube which does not have that particular pin can be bad news, since many amp manufacturers use unused socket pins as convenient solder points for other components. At least one amp has a high voltage connection on an unused socket pin which causes problems if metal pins are used. (In this case you need to either stick with glass tubes, or modify the amp so that the components no longer contact that pin.)
- 7 pin miniature glass
These tubes have a glass "envelope" with 7 metal pins at one end (the base) and a little, glass nipple at the other end (the top). Heights range from about 1" to 2". They are typically 1/2" in diameter. The pins are arranged circularly around the base with a gap between pins 7 and 1 to orient the tube. These are found mostly in smaller amps, esp. among the less common brands. These will usually be rectifiers or preamp tubes, although at least one popular small, power tube (the 50C5) was a 7 pin.- 9 pin miniature glass
These tubes are similar to the 7 pin tubes, but have two additional pins. They are fatter (about 5/8" dia.) and range in height from about 1.5" to 3". Almost all common preamp tubes, driver tubes, inverters, and in fact everything except the power tubes and rectiers in the more common amps (and all larger amps) are 9 pin.- octal (8 pin) glass
These are much larger tubes with a plastic or ceramic, base, 8 larger pins arrayed a center lug with a key on one side to index (orient) the tube to its socket. If a tube uese less than 8 pins, some of the pins may not be present on that tube. The glass envelope is nestled down inside the base. The envelope may stay narrower than the base, grow out to the size of the base or beyond, and may even have a more complex shape, almost like a glass "Coke[tm] bottle". Some such tubes have a contact on top, but these are extremely rare in instrument amplifiers. Octal tubes do not have a nipple on top, the shape of the end of octal tubes varies from almost flat to extremely round. The majority of power tubes and larger rectifier tubes are octal glass tubes. Very old amps may have octal tubes with steel envelopes instead of glass.There are other varieties of tubes, but I seriously doubt you will run across them in instrument amps.
[Introduction] [capacitors] [Resistors] [Tubes]