Filament Voltage and Transmitting Tube Emission Life
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- Опубликовано: 30 окт 2021
- 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! 
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Thanks Tom for your comments. I've been following your comments for years now and find them to be helpful.
Thank you Alan!
@@Jerrythenerdful Great video
As soon as I saw the call sign, W8JI I subscribed! You Sir, are a legend! If anyone is asking a technical question or perhaps is wondering what might be the best antenna, I always point them to your website. Thank you for taking the time to document all that information. Chris, UK.
Thanks!
Cool calm and collective. Very well done Sir.
Thank you. for some reason everyone is posting online that you need to for example substitute a 50c5 for a 35c5 due to todays higher line voltage. The tubes have a +-10% range according to the datasheet. Set was designed for 117 volts. The filament voltage is within that 10% with a line voltage of 105 to 125 volts. I have been measuring the line voltage on the wall outlet for some time now and it varies between 110 to 121 volts but is usually 115-118 volts most of the time. So by keeping the 35c5 I am keeping the set running properly. Replacing it with a 50c5 will yield underheated tubes. all of them in the series string. So this is just more bad advice online that is everywhere.
Well done sir! Good presentation of what ‘should be’ easily understood - often redundantly, needlessly, over-complexified.
Hi , I use large transmitter tubes on my channel for monster Vacuum tube Tesla coils, I would like your advice on a building my own common mode filament choke to keep the RF of my filament transformers in future builds, what would you advise on say the GU39B 100A 6.3v , Ie core size, material, inductance, conductor gauge etc I've used a large powdered iron core in the past 100mm od with around 8t on each side that's all I could get on there because of the large conductors I was using to carry the 100A I also had a cap straight across the pins 470pf 15kv I ran the filament at 6.9v at the pins unloaded to account for the line drop when I start pulsing or running the coil at 10kw cw 😅
Hi Tom!
I searched your callsign on RUclips and here you are! Subscribed instantly.
I found your webpage long time ago, and read everything you write, about antennas and grounding, and I would like to ask you a question, if you please:
I built a quarter wave groundplane for 145MHz, isolated from the mast.
But rain static made it dangerous to use, so I connected the radials to mast and run a 10k resistor from radiating element to radials.
In my opinion it performs well in both configurations, now without static bites.
Which is the best way to build it?
I think you wrote radials shouldn't be connected to mast to avoid losses, and to use an isolator. I like to model and build antennas, but my knowledge is very limited in antenna theory.
Thanks Tom, for sharing your knowledge