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Warming up a tube amp

post #1 of 19
Thread Starter 
When warming up a tube amp do you need to run a signal through it or is it effective just to turn it on.
post #2 of 19

Just turn it on, I'd usually flip mine on 30 - 45 minutes before I was going to listen to it.

post #3 of 19

Running a signal through it and rubbing it like a Genie's lamp usually does the trick for me :D

post #4 of 19

I fire up my Project Sunrise II about 10 minutes before I listen from time to time if I can, but don't run anything through it. 

 

 Generally, I'm grabbing an hour to listen on a whim, so I just fire it up and go. 


Edited by Modular - 12/30/13 at 9:15pm
post #5 of 19
Quote:
Originally Posted by pervysage View Post
 

Running a signal through it and rubbing it like a Genie's lamp usually does the trick for me :D

rawrrrrr... do you ever burn your hands? my tube amp gets quite hotttt&spicy =P

post #6 of 19

I just turn on my amps for a minimum of 10 minutes while I do something else and come back to enjoy some music.  

post #7 of 19
During warm up, no signals should be run through it.

I always use the pre-jogging muscle warmup analogy for vacuum tube equipment.

Before commencement of the actual jog, one has to do muscle stretching exercises.
The stretching exercises are equivalent to just simply turning on your tube equipment.
Speaker amps and headphone amps in general require 30mins or 10mins respectively for this initial
Warm up stage.

After that, u can start playing your audio signals.
This the the start of your "jog".

This ritual can prolong the lifespan of your tubes because u will be making them "exercise" only when they have been sufficiently warmed up for action.
post #8 of 19

Despite the silliness of many posts in this thread, the real answer has to do with the nature of tubes.  They need heat to allow the cathode part of the tube to "boil off electrons."  It is these "free" electrons, that are added to the signal applied at the grid, that produce amplification.  The free electrons are "added" to the signal coming through the grid.  The "plate" of the tube accepts the addition of the signal from the grid with the added electrons coming from the heated cathode.  The result of the output at the plate is a much stronger, amplified signal.

 

All that depends on the heating of the cathode, however.  To reach a thermal equilibrium takes time.  Thermal equilibrium is an inexact condition, usually brought about by the passage of time that is much greater than a few musical songs.  Think how long it takes to boil a pot of water or heat an oven to 400 degrees to cook your pizza.  For a tube to be dependably linear (minimal distortion), that elevated thermal equilibrium must be achieved and it takes time.

 

As for running a signal through - as soon as the cathode is initially heated (30 seconds, give or take) - the tube is going to amplify and reproduce the music signal.  Whether or not a signal is present before or after makes no difference.  It will either produce sound or not.  The best sound will be reached when that thermal equilibrium has been achieved, however. 

 

 

P.S. There is an initial state, depending on the amplifier design, where the accompanying parts of an amplifier (DC-blocking capacitors) have not charged enough to block the DC needed to bias a tube.  That DC, if passed through the circuit, could damage your headphones.  Those things only last a half-minute or so, though, so as long as you don't attempt to listen to a signal in that brief moment after turn-on, everything stated above applies.  Many OTL tube amps are built with a relay-delay to take care of this specific, turn-on condition.

 

Some amps - output transformer-coupled amps, for instance - need no cautions about power turn-on spikes.


Edited by tomb - 12/31/13 at 4:41pm
post #9 of 19
Quote:
Originally Posted by tomb View Post


As for running a signal through - as soon as the cathode is initially heated (30 seconds, give or take) - the tube is going to amplify and reproduce the music signal.  Whether or not a signal is present before or after makes no difference......

I beg to differ about the "before" part.

It will only make no difference safety wise if the tube amp's volume knob is set to the minimum at initial startup.

Can you imagine what will happen if you do a cold start on a tube amp with an input signal already present at maximum volume?

The caps or resistors in the tube amp will give way.

This is why most tube amp manufacturers recommend setting the volume knob to the minimum before the amp is turned on.
post #10 of 19
Quote:
Originally Posted by Lord Soth View Post
 
Quote:
Originally Posted by tomb View Post


As for running a signal through - as soon as the cathode is initially heated (30 seconds, give or take) - the tube is going to amplify and reproduce the music signal.  Whether or not a signal is present before or after makes no difference......

I beg to differ about the "before" part.

It will only make no difference safety wise if the tube amp's volume knob is set to the minimum at initial startup.

Can you imagine what will happen if you do a cold start on a tube amp with an input signal already present at maximum volume?

The caps or resistors in the tube amp will give way.

This is why most tube amp manufacturers recommend setting the volume knob to the minimum before the amp is turned on.


"The caps or resistors in the tube amp will give way."??

Nothing is going to happen to the amp.  Capacitors and resistors are either rated for the voltages that are present, or they're not - warm-up, cold, or whatever.

 

The position of the volume knob affects one thing: the equipment the amp is powering.  If those happen to be headphones or speakers, then yes - they could be exposed to very non-music-type signals during warm-up that could be damaging.  Also, gains may be mis-matched if the equipment the amp is powering has been switched, a new source is selected that's stronger, etc.  It's being conservative to recommend turning down the volume knob.  No amplifier mfr wants to be responsible for destroying your equipment - but it's not going to do anything to the amp. 


Edited by tomb - 3/30/14 at 6:39am
post #11 of 19

I turn it on and by the time I do 10 push-ups on my elbows it's all good to go  

post #12 of 19
Quote:
Originally Posted by tomb View Post
 

Despite the silliness of many posts in this thread, the real answer has to do with the nature of tubes.  They need heat to allow the cathode part of the tube to "boil off electrons."  It is these "free" electrons, that are added to the signal applied at the grid, that produce amplification.  The free electrons are "added" to the signal coming through the grid.  The "plate" of the tube accepts the addition of the signal from the grid with the added electrons coming from the heated cathode.  The result of the output at the plate is a much stronger, amplified signal.

 

All that depends on the heating of the cathode, however.  To reach a thermal equilibrium takes time.  Thermal equilibrium is an inexact condition, usually brought about by the passage of time that is much greater than a few musical songs.  Think how long it takes to boil a pot of water or heat an oven to 400 degrees to cook your pizza.  For a tube to be dependably linear (minimal distortion), that elevated thermal equilibrium must be achieved and it takes time.

 

As for running a signal through - as soon as the cathode is initially heated (30 seconds, give or take) - the tube is going to amplify and reproduce the music signal.  Whether or not a signal is present before or after makes no difference.  It will either produce sound or not.  The best sound will be reached when that thermal equilibrium has been achieved, however. 

 

 

P.S. There is an initial state, depending on the amplifier design, where the accompanying parts of an amplifier (DC-blocking capacitors) have not charged enough to block the DC needed to bias a tube.  That DC, if passed through the circuit, could damage your headphones.  Those things only last a half-minute or so, though, so as long as you don't attempt to listen to a signal in that brief moment after turn-on, everything stated above applies.  Many OTL tube amps are built with a relay-delay to take care of this specific, turn-on condition.

 

Some amps - output transformer-coupled amps, for instance - need no cautions about power turn-on spikes.

Cool, thanks a lot!

post #13 of 19

So everyone agrees on the 10min rule? 

post #14 of 19

I let my tube amps warm up for at least 20 minutes, why?, because the manual says so before biasing the output tubes.

post #15 of 19
Quote:
Originally Posted by tomb View Post

 

As for running a signal through - as soon as the cathode is initially heated (30 seconds, give or take) - the tube is going to amplify and reproduce the music signal.  Whether or not a signal is present before or after makes no difference.  It will either produce sound or not.  The best sound will be reached when that thermal equilibrium has been achieved, however. 

 

 

Thanks, this is the best explanation.  

 

Tube amps for most part are Class A, full current will flow with or without signal, as soon as the filament heats up.  I feed signal immediately when the amp is on.  Due to weak rectifier tube and capacitor charging, my home-built amp will take 4-5 sec for the signal to get to the headphones.         

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