Proper Tube Removal Process?

[big_teee]

I am curious what the proper tube removal process is, while working on an amp.
With a all tube amp that has solid state rectifiers?
Is it ok to put a amp in Standby, which should remove the B+ from all tubes.
At that point change a preamp tube with the Heaters still on?
Or Do you really need to fully power off the Heaters?
I've Seen different things on different Forums.
I want real practical experience from you real Amp Techs.
What you guys do will be good enough for me!
Thanks,
Terry

[Jazz P Bass]

Be aware that you did not specify which amplifier you are talking about.
'Some" amps do not turn off the B+ by the standby switch.
From a tech perspective, I would not recommend 'hot swapping'.
I am of the mindset that the amp should be powered down before I do anything inside an amplifier.
To me, it is simply a common sense approach.

[big_teee]

Be aware that you did not specify which amplifier you are talking about.
'Some" amps do not turn off the B+ by the standby switch.
From a tech perspective, I would not recommend 'hot swapping'.
I am of the mindset that the amp should be powered down before I do anything inside an amplifier.
To me, it is simply a common sense approach.

Mainly old diode rect. type Marshall's, where the B+ Goes through the Stndby.
What I really wanted to know, is not what you say do, but what You guys really Do?
So if you are sorting out 12AX7s, you always power down the Amp?
Thanks for the Reply!
T

[Jazz P Bass]

Me?
Always.

[Jag]

I always power down too.

[Enzo]

It is the flip of a switch, why would I not turn it off?

[Jazz P Bass]

What I do find useful is the way the B+ will hang when the power is turned off.
While monitoring the B+, unit turned off, and inserting an unknown output tube, if the B+ voltage crashes, I know that tube is a fuse burner.

[Mike Burgundy]

car crash investigators determine which lights were on at the *exact* moment of a crash by looking at the broken filaments. There's a difference between filaments that broke all on their own previously, and filaments that endure a crash. But if on, they *will* be broken during the bang.
Handling a tube will not generate anything near that kind of G-force, but it does tell you they are a lot more fragile hot. I think it's likely they are more vulnerable to transients too. It's a tiny action, just power down to be sure.
(Edit: Sorry, not a real amp tech, though, don't do this professionally, but I have made many repairs professionally without at any time calling myself a professional - just the tech around ;P )

[Dave Mac Farlane]

Support for answers - I'll put on my electrical H&S cap and say first - if working live is avoidable - avoid it.
There is nothing to be gained other than introducing unwanted transients by 'hot swapping'.
You cannot withdraw a valve, even with welding gloves, smoothly enough not to cause spikes and back emfs, troughs and all sorts of 'atom bomb' reactions.
Take the advice of these sages - it is unreasonable, and I would reprimand someone who worked for me for doing it.
Dave.

[km6xz]

Pre-amp tubes, yes, power tubes no.

I make sure the tube is cold before swapping or else the inrush on a still hot heater can shorten the life of the heater.
There is no little current flow for the first 11 seconds of standard controlled warmup, a class A preamp, eq etc section is pretty safe with power on swaps, just keep gain and down.
Power tubes are another story if a a side of a push pull transformer coupled amp is pulled or inserted while live. In a 4 tube circuit, with one of the tubes on one side still operating, swapping in a power tube is less problematic. If cold tubes are swapped in live, a cathode biased power stage will not be in much danger either. Just look for any circuit topography where a lot of back emf can be generated by the transformer, or predict how the inrush current will develop in the heater and if it does not look like a candidate for excess peak current in any condition. If there is, error on the cautious side and shut it down. After a short time looking at schematics those traits become obvious and experience honed judgement is enough to guide you.

[big_teee]

This thread, got some interesting Comments and answers, some expected some not.
I talked to several different techs, not on a forum, that said if they know the amp, and know the b+ is switched off through the standby.
They swap preamp tubes with the heaters on, in standby. They all said, they were not telling me to do it.
Everyone I talked to, always turn the amp completely off to change Power output tubes.
T