Swap the tubes between the left & right channels.... just to make sure its tube hiss...

Do the swap, but you are probably hearing some excess gasses or oxidations burning off inside the tube envelope. With the lights off and with the room darkened, observe the tubes when you first power up the amplifier. You want to see all the tubes come up to the same temperature evenly and together. If the tubes warm up evenly and all have a similar "glow" when at operating temperature, there's likely nothing to worry about and the noise will disappear over the next few days. If not, and the noise travels with the tubes, that's the time to call your tube dealer.

If it is the tube settling in- the getter burning in - you want to change tube vendors next time and find one that checks the tubes and does this for you. Most likely they are not matching pairs.

When you don't order matched pairs, you don't get matched pairs. They also sell matched quads. Checkout www.partsexpress.com They have JJ, Harmonix, some NOS, lotsa new I got a whole bunch of different types for spares EL34, 12AX7WP 12AU7 etc etc. Even got some NOS Philips Holland, amperex Holland/USA, all kinds of NOS, good prices and stock The one Russian factory is making most of the brands. Tung-Sol, JJ, Harmonix, Svetlana, and a couple of CZ brands, how many factories are there really making tubes, not many, a few Chinese ones?

Ahhhh, the magic of tubes!

One tip I was given for NOS tubes ( Which I have Not tried ! ) was to bake them in a (food) oven at about 150 deg C, for 3 hours, then shut down the oven, and keep it closed, cooling down overnight.

Next Morning the tubes are good to use.

Any feedback on this ?

I believe you are referring to instructions for resetting the potting material in transformers, not for NOS tubes. A tube runs at several hundred degress, so it is unlikely a 150 degree oven is likely to affect anything in a tube's structure.

Maybe I got the temperature wrong.... but the procedure WAS given to for Tubes, not Transformers.

I also wonder if the Outside of tubes, including the glass envelope would reach several hundred degerees C during regular operation...

Do you also wonder what happens should you apply your tongue to the outside of a frozen flagpole? Look at a tube in operation. Actually, go ahead and touch it. There is a burning, glowing filament a few millimeters away from the glass envelope. And, the glass envelope is the only heat sink that filament has. It is no coincidence it resembles both a light bulb and a space heater. Have you touched one of those while in operation? Now, do you really still wonder about how hot a tube gets?

Just what is your "method" supposed to do to a tube and when would you apply it? There is nothing you can do to a tube at 150 degrees. Even the solder connections require more heat than 150 degrees. What are the symptoms of a tube that would make you use this technique? You certainly can't be trying to restore the vacuum. Once the tube is worn out, it's worn out. What do you expect after completion? And, why only NOS tubes? Who told you this bit of information? What else did they tell you? That you would go blind?

Of course, I meant you would go blind if you sat too close to the television. Of course.

150 C? What kind of oven is that in a house?

I thought this would be as good a time as any to research the net on the operating temp of the glass shell of a audio vacuum tube.

There was a ref ( http://www.harpamps.com/micKtubes/RTV-Tube-Damping.html ) on Tube dampers, which says

" By the way, vacuum tubes are specified for dissipating their rated power at a glass envelope temperature of about 200-250C, according to the data books. What does 3M
O-ring material do at over 200C? Does it decompose, melt, or just quit damping? "

Just out of interest to readers ..... the site recommends
"A workable and highly effective alternative that I've used for quite some
time is the high temperature RTV gasket material sold in auto parts stores.
This gook goes for about $4.00 a tube (of gook, not vacuum...) and one tube will treat MANY vacuum tubes. It cures to a dense silicon rubber..."

So the glass temp does not get near the several hundred degree C mark.

DUP, looks like I'm lucky ?? The oven at my home has a thermostat, that runs from 125 deg C to 275 deg C. !

Anyway, its all besides the point now, that Don L's Tube noise has vanished....

So you can only use metric recipes? Must be one of them thare furon ovens. We should only be cooking with "F" heat, not "C" heat. It will affect the food flaor. similar to how wire heated and cooled affects teh sound.

Ampnut - You must work for the government and have failed to read further into the article from which you draw your "facts".

"Of course, it's preamp tubes that really need vibration damping, and they
usually aren't run that high, but I'd be careful about putting the rings
on high temperature output tubes until I knew it would not melt down into
the tube socket, glueing the tube in, or decompose in place."

A variance in C and F temps seems to be at the heart of our discussion and, as stated above, there should only be F's allowed in any discussion of "tubes". To discuss C's we should instead be discussing thermionic "valves". The usage difference is quite unacceptable under the new Congressional Guidelines of Official Languages. You are excused this time; but, be forewarned, in the future deportation of all non-Official languages and their users will be carried out posthaste.

Quote:

there should only be F's allowed in any discussion of "tubes".

That is SUCH A NARROW View of the world..... !

Infact most of the world now works in deg C .... but then, "World" itself must have a Very Local perspective for you....

Yep, you get it.