I'm now turning my receiver off.

[k4kyv]

For years, I have always run my receiver 24/7, to avoid the warm-up delay and the drift from a  cold start, that even occurs with the 75A-4.  This dates back to when I used the old pre WW2 HRO.

I had been noticing performance on the receiver getting anaemic lately, so before putting it on the bench for a major trouble-shoot, I decided to check the tubes.  I found about a half dozen bad tubes; some just barely moved the pointer of the meter in the TV-7 tube checker.  I  replaced all the weak ones and the  receiver came back to life, even on 15 and 10m, which had gone completely dead.  The xtal oscillator tube was so weak that wouldn't even oscillate on the higher bands.  The 11m band is still dead, but I suspect one of the notorious mica caps in the oscillator circuit.

About 4 or 5 years ago I replaced tubes and had all good ones in the set, so the bad ones had deteriorated over that period.  Now that tubes are getting more  scarce and more expensive to replace, maybe it's time to go into the tube conservation mode, so I plan from now on, to shut off the receiver over night and when I know I won't be using it for several hours.  It will save on the electric bill as well.

My VFO runs all the time too (just the PTO in the modified T-368 M.O. unit).  I seem to  have to replace the oscillator tube about every 3 years or so, so it looks like 24/7 operation shortens tube life.  Like running a computer hard drive, I have heard it debated over the years whether a receiving tube would last longer running 24/7, or cutting power when it is not in use.

One thing for sure, it will shorten the life to run the tube with just the filament lit and no voltage on the plate.  An electron cloud forms round the hot cathode inside the vacuum, with no positive plate or screen to pull the electrons away.  The magnetic field from the a.c. filament current causes the electrons to vibrate back and forth, and in so doing, they sand-blast away the filament coating.  The R-390A manual warns the user not to leave the receiver in stand-by for long periods of time, lest the life of certain tubes be shortened.  The same holds true for transmitting tubes, particularly ones with thoriated coated tungsten filament.  The layer of  thorium is only a molecule or two deep, so it doesn't take much to erode it away.

[flintstone mop]

On the other side of the coin, I do not have a lot of drift on my 390A from a cold start, but I don't think it's good to turn it on and then off in an hour, or so.
Do you have a large temperature swing in your shack? Is it heated for Winter? I noticed that nighttime temps in Woodlawn Tenn are not going below 30 F.
There are still tube sets available for the 75A-4 ($99)and other military gear. They're not too outrageous in the dollar world.
K5SVC has a nice ebay store with toobs
Fred

[Tom WA3KLR]

Don,

I'm glad to hear that you are doing a major overhaul on the receiver.  You reminded me that a couple weeks ago another station and myself (PA and NY) were on 1885 kHz. and heard you calling CQ.   We both answered you but you apparently didn't hear us.

[W1RKW]

Put the receiver on a programmable timer. Have it come on an hour or so before use to warm up and turn off at some time you'd normally quit using it.

I have several items on programmable timers that turn on and off based on the home occupation schedule.  The DSL modem, TV and satellite receivers are on timers.  They suck power when not in use so they're turned off when the house is unoccupied.

[k4kyv]

Don,

I'm glad to hear that you are doing a major overhaul on the receiver.  You reminded me that a couple weeks ago another station and myself (PA and NY) were on 1885 kHz. and heard you calling CQ.   We both answered you but you apparently didn't hear us.

It was probably just condx.  I could still hear any audible signal on that receiver, but the s-meter would just barely kick up and the audio seemed weak.  I could disconnect the antenna from the receiver and the background hiss would drop down, which indicates that the noise  floor resides in the atmosphere, not the receiver.  Even the xtal  calibrator would only hit S-9 or so.  Now it nearly pins the meter on 160 and runs about 30 over on 75.  Looks like I won't need to overhaul the receiver, after all.

I have a spare 75A-4, but it isn't modified to take extra filters, so I am stuck with 3 selectivities with that receiver.  I fired it up the other day, and all was well, except I had to readjust the PTO tuning range. I was able to get it right on the mark with two tries.

[c. mac neill w8znx]

never much worried about drift
just re tune now and then

after my SX-117
slowly cooked its pwr transformer
without blowing the fuse

no longer leave gear turned on
when not in shack
more than 30 min

dit
dit
mac

[flintstone mop]

I might give some thoughts to the programmable timers. Cooking transformers isn't good stuff.

Fred

[Jim, W5JO]

I remember back in the mid 70s when Southwestern Bell replaced their step relay office with the first digital switch in Amarillo, TX.  In that step office there were tubes in operation that were installed when the office went on line in the 1930s. 

The difference is they were operational with all voltages present.  That does make a difference in the longivity.

[Steve - WB3HUZ]

I leave my receivers on all the time. Never had a problem.

[W2DU]

As I've mentioned earlier, my Dad bought our HRO new in 1938. With the exception of the second detector (I believe was the 6B7) all the other tubes are the originals, and are still performing at full capacity, and I used to leave the HRO on 24/7. Pretty good, huh? I replaced the 6B7 with a 6SQ7. This is the receiver I still use on AM.

Walt, W2DU

[N3DRB The Derb]

after the derb-100 meltdown, I turn my gear O_F_F when stopping operations.

[Opcom]

I turn everything on once a month for a few hours.. keeps it alive.