tubes age 154
the Power supply rectifiers. If you do not have the 26Z5 tubes in the power
supply, turning off the plate voltage by switching to stand-by will cause the plate
voltage to raise excessively, and can cause some caps to blow. Never use
stand-by. Probably the best thing to do is to add a CL-80 surge suppressor in
series with the 2 Amp fuse in back. Personally, I don't think tube life is reduced
significantly by turning the receiver on and off. I suppose you will get a few
hundred hours more from a tube that is about to lose it's heater if you leave it
on continuously. The exception is the Ballast Tube. That is rated in cycles
(about 2000-5000). On-Off cycles will definitely affect the life of that tube.
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Date: Sat, 26 Nov 2005 01:00:26 -0500
Subject: Re: [R-390] Tube longevity
Military BAs generally don't beat their tubes (unlike a lot of home hi-fi
equipment), so leaving them on is generally OK. Some oxide-cathode tubes
don't like having no B+ for long periods -- this may argue against the second
option.
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Date: Mon, 28 Nov 2005 20:10:18 EST
Subject: Re: [R-390] Tube longevity (summary)
So what's a body to do? How many hours are you going to listen to the receiver
and how many hours is it going to just sit idle waiting for use? The military run
them 24 x 7 for years. They got turned off twice a year for the semi annual
maintenance. A technician would likely turn it on and off 4 or five times while
doing the maintenance. Once the receiver went back in the rack, it was just left
on until some maintenance guy come along again to do service.
If you only use your receiver once or twice a week, you may as well turn it off
when not in use. If you are going to listen to it every day, even if only for an hour
or so, you should leave it on. If you are going to do a week end event, turn the
receiver on several hours early to let it warm up and stabilize. Then leave it on
for the duration.
A tube has a working life. The military used them 24 x 7 until beyond acceptable
noise performance. At six month intervals, the receiver was tested for signal to
noise performance. Tubes were tested for shorts and put back into the
receivers. The test set up was performed. Maintenance would try to get a 20:1
signal to noise performance out of the receiver. Noisy tubes would be replaced
until the ratio was achieved. The receiver then went back into service for the
next six months at 24 hours a day. 4380 hours. Unless the receiver died, it
received no additional tube changes for about six months. Over this time the
new and old tubes would "age" and get more noisy. Hopefully the signal to
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