# Tube Warm up - what happens before theyre 'warm'



## Tyler Savage (Nov 16, 2009)

I've got an amp with a 6SL7 phase inverter, and I've found that more than any other amp, this one takes about 30-60 minutes to get to a consistent sound, ie: while it 'warms up' the sound seems to change. Now maybe it's ear fatigue but I don't notice this as much with my other amps.

I'm sure I could stick a meter on it and see what's going on (which I may end up doing regardless), but I was wondering if anyone had a good explanation of what is changing while the tube warms up .. passes current better? voltage output not limited as much? 

here's the deal - I LOVE the sound after about 5 minutes, but then after 30-60 minutes it still sounds good but the high frequencies increase and I end up turning down the treble as I go through a set. There's still always a harshness there that wasn't there originally. I'd love to be able to put a mod in to limit the amp and re-create the sound I'm getting about 5 minutes in, but I don't know if this is possible


----------



## dtsaudio (Apr 15, 2009)

There could be any number of things happening here, not just in the phase inverter. You could have another component drifting off spec when the amp gets hot enough, another tube could be the problem, or it could just be ear fatigue. 
Start with the basics. How much playing time are on the tubes? Do you need a tube change?

BTW, what kind of amp is it?


----------



## hardasmum (Apr 23, 2008)

In my experience ear fatigue causes me to turn the treble up, I've never experienced it the other way round.


----------



## WCGill (Mar 27, 2009)

In my experience, most guys like the sound of their amps better when they're nice and warm. Like Dan says, it could be another component that's drifting, coupling cap possibly?


----------



## Tyler Savage (Nov 16, 2009)

dtsaudio said:


> There could be any number of things happening here, not just in the phase inverter. You could have another component drifting off spec when the amp gets hot enough, another tube could be the problem, or it could just be ear fatigue.
> Start with the basics. How much playing time are on the tubes? Do you need a tube change?
> 
> BTW, what kind of amp is it?


it's a garnet rebel PA head. 4-inputs each on half a 12ax7, but I have made them all parallel and generally run them all up about 1/3rd max. 

Given all components 'heat up' to some degree so it really could be any component, but I have another amp with a 6SN7 phase inverter and it seems to do the same thing, and I've read elsewhere that these tubes take awhile to warm up. Tubes are all less than a year old (I play hard maybe once a week) and it behaved like this with the last set in I had.

other amps I have (marshall, fender) I like the sound more when its warm


----------

