Hi Guys,
I'm seeking some opinions on when to turn off a tube amp. The question comes because I just turned off my treasured tube amps to go and cook some dinner. My understanding is that the thing that shortens tube life the most is turning the amp on. Much like cold starting a car.
The amps will be turned back on again in something like 2 hours and herein lies the question. For a shutdown period of 2 hours: Would I be better to turn them off and save 2 hours of life or would I be best to leave them on and save a warmup cycle?
I'm seeking some opinions on when to turn off a tube amp. The question comes because I just turned off my treasured tube amps to go and cook some dinner. My understanding is that the thing that shortens tube life the most is turning the amp on. Much like cold starting a car.
The amps will be turned back on again in something like 2 hours and herein lies the question. For a shutdown period of 2 hours: Would I be better to turn them off and save 2 hours of life or would I be best to leave them on and save a warmup cycle?
Sadface,
There are lots of variables, and lots of opinions.
Please post a complete schematic, with amplifier stages and power supply, and all parts values. That is a good place to start.
There are lots of variables, and lots of opinions.
Please post a complete schematic, with amplifier stages and power supply, and all parts values. That is a good place to start.
My Amp, currently in the repair shop has a reputation for heating up tubes until they glow cherry red unless it's modified. I've only seen it do that trick once in 30 years but that's enough.
It's Safer to turn it off than leave it unattended.
But in any case I get a seven year itch when it comes to tubes and swap them out for better ones before they are passed there use by date. I'm told tubes degrade slowly - so you may not be aware of the slow decline in quality. I swapped JJ input valves and JJ power valves for Genalex Gold Lion and Sophia EL34 before Xmas and was very pleased. Don't swet tube life - have some fun and swap them out once in a while 🙂
It's Safer to turn it off than leave it unattended.
But in any case I get a seven year itch when it comes to tubes and swap them out for better ones before they are passed there use by date. I'm told tubes degrade slowly - so you may not be aware of the slow decline in quality. I swapped JJ input valves and JJ power valves for Genalex Gold Lion and Sophia EL34 before Xmas and was very pleased. Don't swet tube life - have some fun and swap them out once in a while 🙂
If I simplify tube failure to two categories, electrical wear and mechanical wear (from thermal cycle). And lets say your tubes can do 2000 hour and 1000 thermal cycles each, than 2 hours of usage is the same as one on/off cycle.
Hi guys,
I don't think I am allowed to post schematics as they are the intellectual property of Tubes4hifi.com
The preamp is a Tubes4hifi SP14 which is a 6SN7 aikido design. Indepedant regulated filaments on separate transformer windings per channel. Independant maida style regulated B+ at a 265vdc (according to the schematic) per channel but these run off a single 6X5GT rectifier before splitting to the separate B+ supplies. Rk1 is 681ohm, Rk2 is 332ohm. Current stock in there is new stock tung sols. I've got some soviet 6N8s I'm keen to try in here though when I can be bothered popping the hood. We have a 'local' source of these is nicely priced.
The power amps are a tubes4hifi M125. These are essentially a parallel push pull Dynaco Mk3 as far as I can tell. I usually run them in ultralinear mode. Negative bias is 450vdc. The tubes are Valve Art KT88s at the output end and some NOS CV4003s which appear to be Sylvannias but are branded United Electron.
I don't think I am allowed to post schematics as they are the intellectual property of Tubes4hifi.com
The preamp is a Tubes4hifi SP14 which is a 6SN7 aikido design. Indepedant regulated filaments on separate transformer windings per channel. Independant maida style regulated B+ at a 265vdc (according to the schematic) per channel but these run off a single 6X5GT rectifier before splitting to the separate B+ supplies. Rk1 is 681ohm, Rk2 is 332ohm. Current stock in there is new stock tung sols. I've got some soviet 6N8s I'm keen to try in here though when I can be bothered popping the hood. We have a 'local' source of these is nicely priced.
The power amps are a tubes4hifi M125. These are essentially a parallel push pull Dynaco Mk3 as far as I can tell. I usually run them in ultralinear mode. Negative bias is 450vdc. The tubes are Valve Art KT88s at the output end and some NOS CV4003s which appear to be Sylvannias but are branded United Electron.
There is no complete answer, rather a statistical guessing of what will break first.
Power on/off is no real problem with thee amps you mention, as long as the
amp is allowed to be powered off at least 5 minutes before powering on again.
Leaving amp on unattended might be a risk, at least leaving it for more then
a few minutes.
My advice is : turn it off if you will leave more then 30 minutes. Don't
worry about tube lifetime, you will need to replace them sooner or later but
they will let you know when it's time 🙂 The only thing that dramatically
reduces tube lifetime is repeated external testing or tube rolling. Don't !
This is how I see it too.
Valves are a replaceable item. Unless they are very rare or super expensive do not worry about on / off cycles or life time hours.
Another problem is that some valve amplifiers are well made, generously rated, well maintained and run cool (for a valve amplifier) and are happy to be on 24 hours at a time.
Other reputable makes are cooking after a couple of hours or have a reputation for failure, do not even leave the room when they are on!
That goes for any 'doer uppers' or unknown quantities too.
Safest (and best for the planet) is to turn it off when not in use. Heed the 5 minute rule before switching back on too.
Next safest is to always have the amp playing something if you leave the room. Then you can hear it and if it goes quiet - go find the problem...
Alan
And of course, never leave the house with it left on, never leave the house with it left on, never leave the house with it left on x 50 lines 🙂
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Hi Guys,
Thanks for the comments. It seems my thoughts line up with what you guys are saying.
I've generally worked on the idea if the amps are going to be off for half an hour I may as well turn them off for safety's sake. I once had an amp with a bias circuit issue; The bugger red plated a good tube which scared the **** out of me. I'm not sure what happens if you leave a red plating tube on but I sure as hell don't want to find out either. I'm guessing fire might be the result?
Lucky for me these amps are nice and stable; I will admit to having accidentally left them on over night once or twice.
What happened? 😉
Thanks for the comments. It seems my thoughts line up with what you guys are saying.
I've generally worked on the idea if the amps are going to be off for half an hour I may as well turn them off for safety's sake. I once had an amp with a bias circuit issue; The bugger red plated a good tube which scared the **** out of me. I'm not sure what happens if you leave a red plating tube on but I sure as hell don't want to find out either. I'm guessing fire might be the result?
Lucky for me these amps are nice and stable; I will admit to having accidentally left them on over night once or twice.
What happened? 😉
Funny, I built a PP 6L6 amp that was left on for two years straight. (My burn in testing for a new design I came up with). I suggest if you can't leave the house with it on it's not a very good design. It's an amplifier after all, not a candle 😛
I agree, but the important part of your statement is, ''if you can't leave the house with it on it's not a very good design''. As I commented, not all are or modern or 'fettled'.
What happened? Not a lot fortunately. Just the smell of hot wax from the Stereo 20's mains transformer that greeted us. And I learned a certain brand of capacitors is not as impeccable as you would want to believe.
I would definitely switch it off to save energy and for safety reasons, especially when it is a vintage amplifier.
Regarding the original question, on average about two tubes out of 18800 had heater failures when the ENIAC was powered on, so the probability of tube failure at power on was about 1:9400 for each tube, see F. Robert Michael, Tube failures in ENIAC, Electronics October 1947, pages 116...119. DIYaudio member PRR found that this article is available on Internet: https://www.americanradiohistory.com/Archive-Electronics/40s/Electronics-1947-10.pdf
Special-quality tubes were typically designed for 10000 hours lifetime, see their datasheets.
With substantial derating, random failures in tubes can be kept down to about 0.5 % in 1000 hours according to L. Knight, "Valve reliability in digital calculating machines", Electronic Engineering January 1954, pages 9...13. It is probably much higher in your amplifier; when the anodes turn red, they definitely did not derate the tubes.
You can hopefully calculate a break-even point when you combine this information with the number of tubes in your amplifier. But like I wrote, I would definitely switch it off to save energy and for safety reasons, especially when it is a vintage amplifier.
Regarding the original question, on average about two tubes out of 18800 had heater failures when the ENIAC was powered on, so the probability of tube failure at power on was about 1:9400 for each tube, see F. Robert Michael, Tube failures in ENIAC, Electronics October 1947, pages 116...119. DIYaudio member PRR found that this article is available on Internet: https://www.americanradiohistory.com/Archive-Electronics/40s/Electronics-1947-10.pdf
Special-quality tubes were typically designed for 10000 hours lifetime, see their datasheets.
With substantial derating, random failures in tubes can be kept down to about 0.5 % in 1000 hours according to L. Knight, "Valve reliability in digital calculating machines", Electronic Engineering January 1954, pages 9...13. It is probably much higher in your amplifier; when the anodes turn red, they definitely did not derate the tubes.
You can hopefully calculate a break-even point when you combine this information with the number of tubes in your amplifier. But like I wrote, I would definitely switch it off to save energy and for safety reasons, especially when it is a vintage amplifier.
True. Vintage is a different thing. It's nice though, when you build your own amp, that if there's a failure you can fix it easily. After all it's your own build 🙂
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