I don't think you can tell just by looking at it but the tube will have a suffix like 12AX7A the A is for audio use.
The tubes will not make up for sloppy wiring😡
Reading the manufacturer's datasheet is the only way to tell. An A suffix does not necessarily mean 'audio use'; in most cases it actually means 'controlled heater warmup so OK for series heater strings' but it could mean something else.
If you can actually make out the heater wires, they are usually wound helically, which is inherently hum cancelling. Extra measures like tighter helix pitch, etc. are used on reduced hum designs. 7025 and 7199, for example, were reduced hum and noise designs. Funny thing is, on really big tubes, the directly heated filaments are wound hum cancelling so the AC filament current does not induce a magnetic field that physically distorts the heater structure itself. DC would be unusable in these tubes.
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Most heaters are not helical. Only a few (e.g. genuine ECC83, EF86) are. Modern 'ECC83' may not all have helical heaters, as they are really 12AX7 (which originally had normal heaters, but now sometimes have helical ones).
A working professional musician will play 3 to 5 sets
an evening. Generally from about 9 pm to about 1:30 am to 2:am.
For about every 40 mins playing they need a 20 min break.
Then when it starts happening, the sets will naturally lengthen in
duration and they'll join sets staying on stage longer.
They will need a longer break, a 30 - 40 min break after
the longer sets usually before the final set.
NOTE: Some musicians will double book and do an early gig
like a happy hour gig or afternoon party on weekends in addition
to evening gigs which they do 5, 6 ,7 days a week in good times.
Musicians gota pee, drink, smoke, eat, get air, work the crowd, sell CDs,
shirts, etc. They'll typically turn the amps to standby instead of full on.
When the get back they just want to turn standby to ON tune and play.
They don't want to wait for the amps to heat up and stablize....
with cranky bar owners who'll short change the musicians in a
heart beat and think the band never needs a break and over
zealous fans who want to hear and feel the vibe...
...musicians are HIGHLY MOTAVATED for a quick on.
Now, I'm going back to sipping my beer, having two ladies massage
me while I watch a great surf break on a prestine coral beach in
the orient.
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The only way to get a low risk 'quick on' is to not switch off. Maybe the 'standby' switch should just disconnect the inputs but leave the amp running?
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