Tube pre-amps: turn off when not in use?

Adamg, in my experience with 6922s in a DAC I was able to leave them on continuously for four straight years without excessive wear. When I owned a BAT VK3i its 6922s didn't seem to wear prematurely from being left on all the time. The complete opposite was true of my 6SN7 preamp which burned through expensive tubes if I left it on for too long. I am not familiar with the characteristics of the 6H30 which I believe your preamp uses.

I've got a VK-31se. I leave it in standby mode when I'm not listening. I turn it completely off only rarely - when I'll be gone more than 2-3 days. My tubes are close to 3 years of use and still sounding fine. A set of four new Sovtek 6H30 tubes should be less than $100. I have not tried NOS.

Never turn off tube devices. Think about it. You are heating a plate or plates. By turning it off and on you are causing the tube (and plates) to distort their shape each time. You gain many advantages if left on. One, it's "sound" is at a peak and ready for you at any time (versus waiting, for me, an hour). Two, you are not constantly forcing the tube to change the shape and size of all it's parts. (the heating and cooling cycle cause constant stress). Three, the tubes last much longer. I have an Audible Illusion 3A that is supposedly a "tube eater". Well, I've never had it kill a tube yet. I've had some in for years!

Sonofnorway is correct about the standby mode, this is your best option. Do not turn it off, but I would recommend you put it in standby mode.

As for tube costs, the last I checked (8-10 months ago) BAT was charging $200 per tube for what they called NOS 6H30's. FWIW, the price is not going down, only up. I believe BAT was charging $100 per NOS 6H30 about 2-3 years ago, now it's $200 per tube. They claim these are from the 80's, and better than current manufacturer 6H30's. BAT was also selling current 6H30's for $40 to $50 per tube, check with them as I'm not positive here. I remember the $200 price because I had a VK-51SE and the thought of $1600 to re-tube it with NOS 6H30's left a lasting impression.

If you go through other tube vendors instead of BAT you could find 6H30's for as little as $20 each. So to answer your question, no it wouldn't cost you $500-$1000 CDN per year (assuming you're leaving it on 24/7) to keep you preamp running, you could spend as little as $80 a year.
It all depends on how 'good' of tubes you want to put in it, and if you can hear the difference between a $20 tube and a $200 tube. If you get hooked on the NOS 6H30's and leaving the preamp on 24/7, it could get pricey.

I would recommend leaving it in standby, then replacing the tubes every 3-4 years wouldn't be much of an issue, even if choosing the NOS from BAT.

John

Physically, what is happening when the tube is in the standby mode? Is the filament heated, but no voltage on the plate? Are other components kept "warm" as well?