Preamp Tube Life In Lockdown

Classicplayer

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I like keeping quality tubes both EL-84/power tubes and 7025 preamp tubes in my Orange Dark Terror.

After a year in lockdown, I've put a lot of hours on this amp in these past 12+ months. It's amounted to an hour or two daily (or near daily) of playing it. I have changed both power tubes a month ago; just to be on the safe side...knowing that EL84 tubes can wear quickly and (me) also experiencing paying for the amp's repair when a failing power tube put the amp out of comission for a month.

When do you all decide to replace your preamp tubes? Do you change yearly or just when you hear a slight degradation in the amp's sound?

Classicplayer
 

palmerfralick

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I like keeping quality tubes both EL-84/power tubes and 7025 preamp tubes in my Orange Dark Terror.

After a year in lockdown, I've put a lot of hours on this amp in these past 12+ months. It's amounted to an hour or two daily (or near daily) of playing it. I have changed both power tubes a month ago; just to be on the safe side...knowing that EL84 tubes can wear quickly and (me) also experiencing paying for the amp's repair when a failing power tube put the amp out of comission for a month.

When do you all decide to replace your preamp tubes? Do you change yearly or just when you hear a slight degradation in the amp's sound?

Classicplayer
when they fail. I use old tubes I have bought years ago or recently. Brimar pre-amp tubes are a favorite. All of my pre-amp tubes were bought used so I have no idea of their previous hours. Cant go wrong with a 1960's RCA preamp tube. Sorry this probably was no help to your application but I play a DSL20HR about 30 -45 minutes a day. Pre-amp tubes will start making a noise when they need replacing and you just tap them with a chop stick to find the offender.JAN 7025 tubes would most likely outlast your ownership of the Orange. We all get another amp sooner or later just remove the JAN 7025's when you sell it. Cheers
 

ErictheRed

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I pretty much change tubes when they fail, though occasionally I've changed power tubes out when I notice a perceived lack of volume or headroom (not always the fault of the power tubes, obviously). But if it ain't broke, and all that.
 

northernguitarguy

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I have a pair of Dutch, Rogers branded Philips tubes in my Orange. I’ve been using them for over six years in a main amp and they still test strong.

TBH, I’ve never had a preamp tube fail me.
 

ErictheRed

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Yeah in my experience, when a preamp tube fails you really know it. It's power tubes that can still sound good at lower volumes but not keep up at higher volumes.
 

Mark_the_Knife

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When something goes wrong with a tube amp, the process of determining what went wrong can be daunting. As most users have noted, the failure rate of preamp tubes is fairly low. I would perform annual tests of the transconductance, and record the values in a notebook. The nominal value for a 12AX7 is around 1200 micromhos. Tube testers from the 1950's to 1960's will have a booklet giving the acceptable working range of this spec.

When it comes down to testing, always have at least two reference tubes you keep in a drawer for testing purposes. Assuming the rest of the amp is working fine (meaning the power tubes, rectifier, and filter caps are OK), swap out the existing preamp tubes for the reference ones, and perform an audio test. If you can't hear a difference, then your current tubes are probably functioning fine.
 

musicmaniac

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I replace them when trying another tube or when they're defective.
 

rabidhamster

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I’m not familiar with an instance of a failed preamp tube damaging an amp so no need to change if they sound good. Usually they just the stop working and break the signal, often they get low and intermittent or really distorted and noisy, sometimes they only get squeally. No big deal. If your amp still sounds drab it doesn’t hurt to change them, I’d save the old preamp tubes for spares.
 


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