Tube/valve life

[Brendo]

What's the average lifespan you might get out of a set of preamp tubes? Poweramp tubes?

I've had my amp for 3 or 4 years now, running it at about halfway all the time, so the tubes have probably 2000 hours on them by now.

Stock Marshall EL84's in the power section, I've gone through and changed out some of the preamp tubes.

[Tim Armstrong]

Wildly variable!

Tim

[Brendo]

If I'm noticing my amp is very midrangey nowadays, and isn't quite sounding right anymore... time for a valve change?

[seaneldon]

If I'm noticing my amp is very midrangey nowadays, and isn't quite sounding right anymore... time for a valve change?

This symptom is not one that I typically associate with kaka tubes. Other components aging? Sure. But not the tubes.

Is it perhaps that it's especially light on bass and treble ranges? Is the bottom really mushy? That could be power tubes going south. You wouldn't notice any major (or any at all) power reduction with power tubes going...eventually, you'd repeatedly blow fuses instead.

Preamp tubes going dying sounds nothing like you describe. When your clean channel becomes a Boss pedal distortion, or if the amp goes microphonic, your preamp tubes are dying.

Try another speaker or patching in another cabinet. If you're halfway competent with disassembly/reassembly, open her up to look for puffy or leaking caps.

[Tim Armstrong]

Yeah, usually if you start noticing significant changes, swapping in new tubes is the first thing to try. Preamp tubes first (because they're cheaper, and it's easy to have a few spare 12AX7 tubes handy). Then power tubes, and it's often useful to have a tech bias the amp (kinda like adjusting the idle on a car) so the amp doesn't either sound like crap or burn up the tubes...

Tim

[Jasco]

What's the average lifespan you might get out of a set of preamp tubes? Poweramp tubes?



For what it's worth:

I'd change my power tubes about every two years when I was on the road - 4-5 nights per week, 3-4 hour shows, amp dimed. Plus lot's of bumping around for travel.

I don't know if they needed it, but it usually seemed the amp had a little more life after new tubes and bias.

Never had a problem blowing tubes at a show (although I did seem to blow a transformer about once every 2-3 years.)

Preamp tubes I'd almost never change unless they turned microphonic.

[radeng9805]

open her up to look for puffy or leaking caps.

Caps can go bad without showing anything wrong on the outside. High ESR in coupling caps can change the tone for sure. An ESR meter is one of the best test equipment buys you can make. They can be used in-circuit without disconnecting any leads. High ESR can screw things up worse than the cap drifting in value a bit.

[onze_jef]

I 'd say time for an ampdoctor. Doesn 't have to be expensive and on the long run it saves money to keep your shit maintained.


If I'm noticing my amp is very midrangey nowadays, and isn't quite sounding right anymore... time for a valve change?

[seaneldon]

Caps can go bad without showing anything wrong on the outside.

Very true.

But when they actually SHOW something wrong, you know what's probably wrong!

[Brendo]

Is it perhaps that it's especially light on bass and treble ranges?Yeah. I said midrangey.

Is the bottom really mushy? That could be power tubes going south. You wouldn't notice any major (or any at all) power reduction with power tubes going...eventually, you'd repeatedly blow fuses instead.Not blowing fuses - but yes, mush city.

Preamp tubes going dying sounds nothing like you describe. When your clean channel becomes a Boss pedal distortion, or if the amp goes microphonic, your preamp tubes are dying.Fairly sure the preamp tubes are cool.

Try another speaker or patching in another cabinet. If you're halfway competent with disassembly/reassembly, open her up to look for puffy or leaking caps.Another cab sounds ok, less 'midrangey' - but still mushy.

[nobby]

What's the average lifespan you might get out of a set of preamp tubes? Poweramp tubes?

I've had my amp for 3 or 4 years now, running it at about halfway all the time, so the tubes have probably 2000 hours on them by now.

Stock Marshall EL84's in the power section, I've gone through and changed out some of the preamp tubes.

Be careful crossing the street, or I will have power tubes that outlast you!

[QUOTE=Tim (tarmadilo) Armstrong;220043]Yeah, usually if you start noticing significant changes, swapping in new tubes is the first thing to try. Preamp tubes first (because they're cheaper, and it's easy to have a few spare 12AX7 tubes handy). Then power tubes, and it's often useful to have a tech bias the amp (kinda like adjusting the idle on a car) so the amp doesn't either sound like crap or burn up the tubes...


I have a lot of tube gear, so I have a tube tester.

A tube tester tests for obvious stuff; emissions, leakage, shorts;

Beyond that, preamp tubes are prone to microphonics, which don't show up in tests as far as I've been able to determine, but which are obvious in terms of self feedback. When you tap a preamp tube and that sets off feedback, that's your indication.

Hi gain combo amps are the worst in terms of peamp tube microphonic feedback due to the lack of separation between the amp and and speakers -- at least that has been my experience.

[Brendo]

Well, I'm also looking for a bit more "chime" and "jangle" in my clean channel, a little more top end basically. Would changing from the stock (probably chinese) Marshall branded EL84's to another brand help?

[onze_jef]

It would be more effective to change the 1st preamptube. Go to someone who has a lot of old and new tubes in stock and try 'em, the difference in tone and grain can be spectacular.

When you swap preamptubes you dont need to rebias. That means you can get yourself a couple and change 'em anytime you want to get different sounds.

Well, I'm also looking for a bit more "chime" and "jangle" in my clean channel, a little more top end basically. Would changing from the stock (probably chinese) Marshall branded EL84's to another brand help?

[nobby]

Paging Zoesch

.

[Bob Olhsson]

...Hi gain combo amps are the worst in terms of peamp tube microphonic feedback due to the lack of separation between the amp and and speakers...The best lead guitar sound I ever got was a tan Bassman with microphonic preamp tubes sitting on a HiWatt cabinet. Thankfully the technician who "fixed" it gave us back the old tubes.

[onze_jef]

The best lead guitar sound I ever got was a tan Bassman with microphonic preamp tubes sitting on a HiWatt cabinet. Thankfully the technician who "fixed" it gave us back the old tubes.


For leads I believe you, but I 'm affraid in the context of heavy rhythm a microphonic tube ain't exactly the way to go...

Unfortunately those Old tubes are much better made then new ones and those few times I compared different preamptubes (someone was swapping them for me and I did not know which one was selected) the ones that had the nicest tone and grain to my ears were really old ones, even for "modern" sounds.

[Bob Olhsson]

It worked really well for rhythm riffs too. The player has the biggest "touch" I've ever encountered too.

[Brendo]

i think i've already gone through a year or two ago and changed out preamp tubes for a few different ones to get a bit more sizzle in the gain channel, which in theory shoulda given me more chime in the clean. possibly worth re-evaluating? it was the first position tube that i was changing out, i think there's a groove tubes in there or maybe a sovtek.

[seaneldon]

i think there's a groove tubes in there or maybe a sovtek.

Please, call them by their scientific names: Bad and Worse.

[Brendo]

cant be worse than the stock tubes that it came with, can they? marshall branded, i'm assuming chinese.

[nobby]

Sovtek are pretty much the cheapest along with electro-harmonix, I think.

But that reminded me, I havent checked the tubes in my Marshall in quite a while.

Hmmm... 3 out of 4 power tubes test bad for emissions :p

Just ordered a matched quad of NOS Svetlanas for $118 :Roll eyes:

They should last a couple of years though. Brendo, the power tubes that are older than you are are in the '68 Dual Showman.

Marshalls tend to tax the EL34s pretty hard (not sure about power tubes in their smaller amps) and they need replacing more often, but if you want that sound...

[Brendo]

Well, these are EL84's, not EL34's... and it's a combo amp.

Think "tube life in an AC30" if that helps.

[nobby]

Well, these are EL84's, not EL34's... and it's a combo amp.

Think "tube life in an AC30" if that helps.

It doesn't really. My small combo amp is a '65 Deluxe Reverb (6V6 x2), a completely different animal AFAIK.

[Brendo]

Right... well I seem to always hear that EL84's are not long for this world when placed in combo amplifiers... due to heat issues.

[nobby]

I don't know why a combo would get hotter than a head.

More vibration, maybe...

[Brendo]

Heat rises, right? And in a combo amp the tubes are mounted upside down, so at the top of the amp... the heat collects up near the tubes and circuit board.

[nobby]

I could see the heat having an effect on the resistors, caps, etc. over time.

The only combo amps I have are pretty old; the '65 Deluxe Reverb, and a couple of smaller practice amps from the same era. The tubes seem to last fairly well in the Deluxe.

I have a lot of tube gear (7 guitar amps, 4 preamps and a stereo amp) so it would be a bit OCPD for me to keep charts on tube longevity -- I just test the tubes periodically to make sure that if they are going bad they get replaced.

[nobby]

The best lead guitar sound I ever got was a tan Bassman with microphonic preamp tubes sitting on a HiWatt cabinet. Thankfully the technician who "fixed" it gave us back the old tubes.

I consider microphonic tubes to be a problem when you can't turn the amp up with out it squealing.

That's the problem I had a few years ago with a borrowed Mesa Dual Recto 100w combo amp. I had to disconnect the speakers in the amp and patch it to a separate cab in order to use it.