how much volts does it take to heat up a filament in an electron tube?

Question

just wondering

Answer 1

There were a whole range of voltages that could be used. It depended on what minimized the total cost of the gadget the tube was in. If it was a single tube cheap phonograph for kids the one tube had a filament that worked at 115 volts. If it was a TV with a lot of tubes with their filaments in parallel then there was a transformer (usually 6 or 12 volts) and every tube had a filament to match that. If it was a cheap radio with a handful of tubes and no transformer then the total voltage across all those tube filaments in series added up to the 120 line voltage (including some that were running at 35V and others that were at 12 volts). Early TVs with isolated high voltage diodes used a tiny 1.5 volt transformer and had tubes to match that. Most military radios had 24 volts. Most old car radios had 6 volts.

Answer 2

The filament voltage was generally the number at the beginning of the tube part number. For example, the 6V6, 6L6, 6AQ5, etc.,etc. required 6.3 Volts for the filament. The 12AT7, 12AU7, etc. required 12.6 Volts but included a center tapped filament where the two halves could be run in parallel at 6.3V. Other types (50C5 - 50 Volts, 35W4 - 35 Volts) were generally designed for a particular filament current allowing series connection of the filaments for direct connection to the line voltage.

Answer 3

Its really going to depend on the gases filling the space around the filament, and the filament material. If you are referring to tungsten the common filament then its somewhere in milliseconds range before heat occurs and something like .2 seconds before light emission.

Answer 4

I depends on what the tube was designed for. As I recall, (yes I am actually old enough to have used vacuum tubes, but it was in a kit when I was a kid) about 6volts was common for consumer type tubes (radio receivers etc)