What is an octal tube?
An octal tube is a vacuum tube that has an 8-pin base with an 11/16″ diameter keyed locating prong called a spigot in the center. This tube base was introduced by RCA in 1935 for their new line of metal tubes, which they called an “Octal base”. Some common octal tubes are 6V6GT, 6L6GC, EL34, 6550, KT88, 6SL7, and 5AR4.
What are microphonic tubes?
Microphonics describes the phenomenon where a tube transforms mechanical vibrations into an undesired signal (noise or feedback). Due to the mechanical construction all tubes exhibit some inherent microphonic tendencies. Most technicians will handpick the first preamp tube for the least noise and microphonics.
What is a tube socket used for?
Tube sockets are electrical sockets into which vacuum tubes (electronic valves) can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins. Sockets are designed to allow tubes to be inserted in only one orientation.
What causes tubes to go microphonic?
Microphonic vibrations are most often caused by internal component electronics like transformers, relays, motors, and external vibrations like sound waves. Internal tube vibrations are caused by alternating opposing charges between plate and filament, which cause those parts to vibrate.
How do you fix a microphonic tube?
Try the following:
- Remove the power tubes. Remember the way the eight pins are arranged, and note that the center hole on the socket has a keyway that matches the center post on the tube.
- Replace one tube. Turn the amp on again.
- When the tubes have cooled, remove them. Replace the power amp tubes with new ones.
How do you test a microphonic tube?
Lightly tap on each tube with the eraser end of a pencil and listen for a ringing or rattling noise. Tubes that are not microphonic will be quiet. bad, microphonic tubes will sound like a bottle with springs in it.
How do you clean vacuum tube sockets?
Apply a little bit of red “De-Oxit” or other high quality contact cleaner (must be safe for plastics) to the pins of the tube. CAREFULLY re-insert the tube, and “scrub” the socket by carefully removing (almost but not quite all of the way out) & inserting the tube several times. That’s it!
What is microphonic effect?
Microphonics, microphony, or microphonism describes the phenomenon wherein certain components in electronic devices transform mechanical vibrations into an undesired electrical signal (noise). The term comes from analogy with a microphone, which is intentionally designed to convert vibrations to electrical signals.
What does a microphonic tube sound like?
One common symptom of a microphonic tube is hearing a lot of static or a feedback sound. Lightly tap on each tube with the eraser end of a pencil and listen for a ringing or rattling noise. Tubes that are not microphonic will be quiet. bad, microphonic tubes will sound like a bottle with springs in it.
Can power tubes go microphonic?
For example an amp where the reverb is malfunctioning indicates the tube in that part of the circuit needs to be replaced. Output tubes can also be microphonic.