valves,(tubes) re biasing

[gordiji]

Is it a good idea to have an amp re biased for new poweramp valves.I've never done so before ,but only out of ignorance.Only knew what re biasing was since i started googling stuff recently.Normally i'd ring valves r us, get the
matched pair set recommended by the 'expert' and bang 'em in.
Is it a good idea to replace them before they go pop? say after a few hundred hours.
And then what about pre amp valves?
 

[maverickf1jockey]

To an extent the amp will dictate its own maintenance requirements (Much like a car has varying components and mechanical parts the circuits of amps all have their strengths and weaknesses despite all doing roughly the exact same thing.).
As a general rule Preamp valves shouldn't require bias and some models don't require any bias whatsoever (these are mainly British-built and designed amps like Marshalls, Oranges, Hiwatts/Hilites/Sound City's.) as the power amp valves have a fixed bias and just need to be matched to a reasonable tolerance.
Other amps can be biased relatively easily to get the optimum level of performance.
:Awaits the other members who actually know something tangible about the workings amps to debunk his information:

[HTH AMPS]

assuming you're buying current production output valves and not NOS and you're gigging maybe 4-6 times a month (weekend warrior ahoy!!!) then you should easy get 12 months out of a set of EL34s/6L6s etc...

the thing with valves is you never know when they'll go or in what manner.  some just wear out and start to sound dull, or lose power, or fluctuate in volume.  others will go out in a blaze of glory and take some minor components with them.  For most amateur players, you'll easy get 18-24 months out of them.

imo, its a better investment to buy NOS valves - they sound a million times better (yes they do, this is not open to debate) and also last longer.  its a no-brainer to me.

[BigB]

Is it a good idea to have an amp re biased for new poweramp valves.

(warning: I'm not a qualified amp/tube tech in any way - just joe average guitarplayer)

Depends on your specific make and model. Some are fixed bias - so you need to have specifically matched tubes-, some are adjustable bias - then you should indeed have the amp rebiased when swapping tubes -, and some (mostly el-84 based amps AFAICT) are "auto-biasing", so you just don't care.

NB: please someone correct me if I said something wrong   :?

Is it a good idea to replace them before they go pop? say after a few hundred hours.
And then what about pre amp valves?

I don't know of any amp that requires rebiasing preamp tubes (which doesn't mean such a beast doesn't exists).  And yes, it seems obviously better to replace your power tubes when they start to wear out - first because you may not like the sound of aging tubes, but mainly because, as HTH mentioned, a dying tube can sometimes damage your amp.

Now how long your tubes will stand before needing being replaced depends on both your amp and how you use it. For the record, my old 100w marshall's tubes lasted litterally for years - but I didn't used it much and only at very low volume. I don't even hope my Blues Junior's will last that long - use it quite intensively at bedroom level and at least 6 hours a week almost fully cranked up  :mrgreen:

So yes, better to watch out for wear signs IMHO (they are described on quite a couple places on the net) and/or have a qualified tech check your amp on a regular schedule.

My 2 cents really - not an expert in any way, and there are way more qualifed guys hanging around here  :?

[HTH AMPS]

further to BigB's post, he reminded me of something I've seen many times - vintage amps from the 60s still with the original valves, working and sounding great.  thats a testament to the quality of NOS valves.  I can't imagine some Svetlana EL34s still working in a gigging amp 40 years down the road.

it's like putting remoulded tyres on your car versus a decent new one.

[gordiji]

Thanks for sharing your wisdom HTH (and all), let me share my ignorance. Wtf are NOS , i'm guessing something original spec.   I did have a Fender super 60 years back that did five years and hundreds of hours but when one of the output valves popped it caused a 'flashover'( according to my amp tech). I never relied on it again.
Also a fender 'pro sonic' that went bang after a year although it was gigging 3x a week.Traded it for a twin.
Got an engl screamer now but i'm only bedroom bashing(no neighbours) so reliability isnt the key issue, but i think preventative medicine is better than reparative.

[HTH AMPS]

NOS = New Old Stock. 

basically, valves made during the heyday of production (pre-1980s) that have been stored and not used.