Cycling the Switches

[Jerry-n5ugw]

I have a question concerning turning ON and Off the filament and HV supplies. My routing is in the morning to turn on the Fil & hv warm them up , talk and then tunr them off. I do the same in the afternoon. So i'm daily cycling the fil's on and off, on and off.
What is recomended here, continue to cycle them for safety's sake of leave them on for longevity's sake..

 

[flintstone mop]

Jerry
If it's a commercial piece of gear or military built, it's ok to leave on 24/7 except during the Summer or bad Winter wind storms where the power is going to be up and down and full of surges. Or if you're operating time is just on weekends.
If they are consumer pieces, then stick to the sched you now have.

Fred

[k4kyv]

I'm not sure that leaving the filaments on 24/7 makes the tubes last longer.  On contrary, it may actually shorten life.  The electron cloud that is generated around the heated filament in the vacuum is set into vibration by the magnetic field  resulting from the a.c. filament current.  These vibrating electrons sandblast away the micro thin coating of Thorium that coats the tungsten filament, designed to greatly enhance the emission qualities.

RCA recommends cutting off the filament voltage to transmitting tubes if the planned stand-by period is to be for two hours or longer.  During shorter periods of stand-by, they recommend cutting the filament voltage down to 80% of normal.

But NEVER run the tube at reduced filament voltage, enough to cause any measurable drop off in peak plate current.  That will shorten tube life as much or more than running the filament at excessive voltage.

Tube life may be extended by carefully reducing the filament voltage to just a hair above the point where there is a perceptible decrease in peak plate current, and keeping a close eye on operation.  But unless you have well calibrated instruments to measure peak plate current and a.c. filament voltage, best bet is to follow the manufacturers recommendation and run the filaments to within 5% of the nominal voltage.

The same goes for receiving tubes.  I stopped running my 75A4 24/7 when I noticed short tube  life both in the receiver and the outboard monitor amp, even with plate voltage applied.  Running the filament with no plate voltage may have the same effect as with transmitting tubes.  The R-390A operating manual cautions the user not to run the  receiver in stand-by mode for long periods of time because it "may shorten the life of certain vacuum tubes".

[K1JJ]

I have to agree that it's best to leave gear OFF when not in use.

When I was a young tech, I remember the head engr (my boss) coming into the lab and asking why I kept the test gear running that was not being used.  I figgered it was OK to leave it on all the time. 

He said, "Keep the hours off the equipment."  I think he knew there's lots other other things that can shorten gear life too, like electrolytics drying out from heat as well as certain tubes crapping out. 

There's something to be said of the bad stress each warmup cycle puts on gear, but I think it gets outweighed by the benefits of gear being in suspended animation for long periods of time.  (in a dry, warm room)

Anyway, I pull the breaker in my shack for all gear when not actively being used. The electric bill is better too, as well as the fire hazard.

T

[Todd, KA1KAQ]

The R-390A operating manual cautions the user not to run the  receiver in stand-by mode for long periods of time because it "may shorten the life of certain vacuum tubes".

Wonder if it has anything to do with the B+ soaring in standby mode? The 2 hour rule is the one I try to follow unless it's a busy weekend of radio, in which case I'll leave stuff on and get back to it as time allows. If you're not absolutely sure you're going to get back to it soon, turn it off or you'll come back from a trip to the store, working outside, or whatever to discover your gear still cooking away.

Articles I read in the past about on/off fatigue issues seemed to deal more with entertainment radios and people shutting them off every time they left the room, only to turn it back on a few minutes later. I wouldn't think transmitting tube filaments would be quite as delicate.

Tom, I decided to use the same approach with the new radio room and got a panel with the large disconnect breaker built in. Throw that, everything is cold. I'll hafta run a dedicated circuit from the garage just for the old analog clocks, other than that it all stays off when not in there. A number of old tube receivers have 'damp chasers' or leave the VFO tube filament lit to help with stability. Better safe than crispy!

[ke7trp]

Turn it off.  I tried this with recievers over the years. Next thing I know I was replacing tubes.

The main reason I turn my gear off and flip the variac off when not in use is safety. After having the Choke fail on my valiant while I was asleep, I learned my lesson. It nearly cost me everything.  Dont trust old gear.. Even if I run to the store for 10 minutes, I turn it off.

Clark

[k4kyv]

I have considered ganging the power switch with a variac, like the combination on/off-volume control on old radios, to feed all the tube gear.  That way, when you turn it on, you have to manually rotate the variac to full strap before the equipment gets full  line voltage.  That gradual application of line voltage should eliminate the surge from hitting the cold filaments with full voltage with a simple switch.

My outboard receiver amplifier, a 1950's vintage 10 watt hi-fi dumpster find, used to require a new pair of 6V6's about every 9 months.  I used a bucking transformer to reduce the input voltage to 110v, down from the 120-125 volts we get here, and that, combined with turning it off over night, has extended time between tube replacements.  It's been well over a year now, and the latest pair of 6V6's is still going strong.

[ke7trp]

Don. Good to talk to you..

That is exactly what I do here. I have a 30 amp Variac on a dedicated line. This runs to a heavy power strip. An old RCA power line monitor is plugged in and visable.. I just rotate it up to 117. My static line voltage is 126 here in AZ. Way to much for the filiments.

Talk to you soon!

Clark
Ke7trp