When to power off a tube amp?

Bifwynne:
Tube failure or arcing (flare up) happens in nearly all cases when the amp is first turned on from cold. This is because the HT comes onto a cold tube.

One way to rectify it is to get a 30sec delay circuit for the HT, so the heaters have a chance to heat the anodes and cathodes first. If you cannot build one yourself then there are many pre-made ones to insert on the HT rail.

Just Google or look in ebay for "Relay Delay Circuit" Do the math as you have high volts small current to give the relay contact amp rating you need. They can be bought for around $10 ready made. In the case of mono blocks you need two.

Or if this is too much bother, then just have another manual switch which breaks the HT so you can bring it on 30sec later, after the tubes have warmed up.

Cheers George

FWIW, a few years ago I installed a brand new quartet of Chinese-made 6SN7 small signal tubes in my VAC amp, that had been provided and tested by a good supplier. After listening to beautifully reproduced music for about 2 hours, all of a sudden there was an eruption of horrific static-like noise from one speaker. I believe it was loud enough, and that it had sufficient high frequency content, to destroy the tweeters in many speakers if allowed to continue for a prolonged period. In this case I had the amp shut down within about 4 seconds, with no damage. I subsequently found that one of the 6SN7's had abruptly developed a short.

I of course have never used any of those four tubes since.

FWIW. Regards,
-- Al

1. General consensus is that for safety purposes, it's not a good idea to leave a tube amp unattended for any significant period of time. In my case, that means if I leave the house, I turn it off.
2. Let 'em warm up if you want, but no reason not to listen if you want to. It can't hurt the tbes.
3. If the amp is has tube output tubes, it's not a good idea to run them w/o a load, i.e., headphones.

I've never heard a good reason to leave them on after listening as they warm up within five to ten minutes. I've never had an explosion but there is enough plastic volume in the boards to get a good roaster that could catch a pair of drapes on fire. I'd say even though you can burn down the whole neighborhood on occasion, tubes are worth it.

Many recent vintage tube preamps have a slow start cycle built in. It slowly increases the voltage going to the tubes over a 20 to 45 second interval when you turn the preamp on.

Preamps that I know of with this feature include PrimaLuna, c-j and Aesthetix. If your preamp has this feature, I think you should turn it off if you won't be using it for an hour or so. The life of small signal tubes is being used up even when music is not being played through them, although at a slower rate than when music is being played through them.

I am not a tube or electronics expert, so if i am wrong about this, please correct me.