Capacitor

Capacitors is a passive electrical component consist of two equal but opposite charge plates, separated by a dielectric. It is use to store electrical energy temporarily in a electric field.

There are different types of capacitors use in tube amplifier circuit,

Polarize capacitor likes electrolytic capacitor which have positive(+) and negative(-) must be installed correctly if not it will behave like a dead short and blow. The negative (-) lead should be the one grounded.

Non-polarize used as your coupling capacitor, they are banded  to show which lead is outside the foil which can be serve as a shield against Electromagnetic interference. The banded lead should go to the proceeding plate. If used as a bypass capacitor the banded lead should go to the HT B+.

Typical value you will see in a tube amplifier circuit is

0.22uf = 0.22 x 1/1000000 = 0.00000022 Farad
470uf = 470 x 1/1000000 = 0.000470 Farad
47uf = 47 x 1/000000 = 0.000047 Farad

Capacitance are measure with Farad, since it was too small, we measure it in mili(mf), micro(uf), nano(nf) and pico(pf) Farad

Voltage rating is very importance in capacitance. It directly related to his dielectric which mean how many voltage it can withstand before shorted and blow. Always use the right voltage rating. There are different material used as dielectric, likes paper, polypropylene film, polyester film, mylar...etc. Each of it have it own pros and cons.