Top cap
Encyclopedia
In vacuum tube
trechnology, a top cap is a terminal at the top of the tube envelope that connects one of the electrodes, the other electrodes being connected via the tube socket
.
Top caps have most commonly been used for:
A few amplifier tubes used two top caps, symmetrically placed, one for anode and the other for grid.
In audio amplifier tube application, the top cap was originally used for the grid connection, and a serviceman could apply a moist finger to the terminal to confirm that the stage and subsequent circuits were working by listening for the hum this produced in the loudspeaker. This practice led to some nasty accidents when anode top caps were first introduced to amplifier stages (they had been used on rectifiers for some time).
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
trechnology, a top cap is a terminal at the top of the tube envelope that connects one of the electrodes, the other electrodes being connected via the tube socket
Tube socket
Tube sockets are electrical sockets into which vacuum tubes 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 plugged in in only one orientation...
.
Top caps have most commonly been used for:
- Amplifier or similar tube control gridControl gridThe control grid is an electrode used in thermionic valves used to modulate the flow of electrons in the cathode to anode or plate circuit.- Operation :...
connection, to provide greater circuit stability by isolating the low-signal circuit from the rest of the tube connections.
- AnodeAnodeAn anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
connection, to isolate the high-tensionHT (vacuum tube)__FORCETOC__In vacuum tube technology, HT or high tension describes the main power supply to the circuit, which produces the current between anode and cathode...
circuit, allowing higher voltages to be used.
- Physical convenience. Grid top caps on frequency converters could be connected directly to an adjacent coil; Anode top caps on output tubes could be connected by flying leads directly to an output transformer. Shorter leads generally mean greater stability.
A few amplifier tubes used two top caps, symmetrically placed, one for anode and the other for grid.
In audio amplifier tube application, the top cap was originally used for the grid connection, and a serviceman could apply a moist finger to the terminal to confirm that the stage and subsequent circuits were working by listening for the hum this produced in the loudspeaker. This practice led to some nasty accidents when anode top caps were first introduced to amplifier stages (they had been used on rectifiers for some time).