This video explains how to set filament voltage properly for amateur radio amplifiers. It explains why filament voltage in Ham radio amplifiers should never be set on the low side of filament voltage range. It also shows how to measure filament voltages properly.
I would have liked the video to have explained how current increases because resistance decreases in a depleted thoriated tungsten filament tube. This would have made it even longer.
The important takeaways from this video should be the following:
1.) NEVER measure the transformer secondary and assume that is the tube pin voltage! You must measure at the pins with a warm filament transformer and hopefully at a period of your lowest line voltage.
2.) Never run at or below minimum filament voltage. Articles telling you to do that are just flat wrong. We are better off to set the filaments so at lowest operating voltage the filament is something above the minimum range. Life at low voltage, where the filament is colder than normal range, is shorter than a filament operated too hot, plus any amplitude modulated (including SSB) signal will splatter.
3.) If a new tube has really short emission life and goes flat within hundreds of hours it is almost certainly a manufacturing defect. This is why I test and sort my tubes by absolute peak emission using a pulse, rather than just RF carrier output in an amplifier. Peak emission far more often shows a poorly manufactured tube.
4.) Grid current has little to do with tube life in thoriated tungsten tubes. It is critical in oxide cathodes.
5.) Don't age tubes in, or "precondition" tubes, with reduced filament voltage. Especially do not precondition them with anodes tied to grid and AC applied.
My old legacy website www.w8ji.com has specific tube articles in the amplifiers section. That site is no longer editable since it was a Frontpage based site established around the late 1990's . Thank you!
30 окт 2021