Valve replacements

suspiciousminds

In a valve amp how often should the valves be replaced?
Do they suddenly pack up or do they degrade over time?

ICBM

1 - It depends

2 - It depends

Sorry - there's no clear answer. How long they last depends on the amp design, how often you use it, at what volume, and the quality of the valves.

They do all slowly degrade over time, but *very* slowly - it's usually outweighed by the other factors. They can also fail without warning. Different types of valves last different amounts of time and show different failure symptoms too…

*Do not* just change all the valves at once, unless you like throwing away money and good valves. They never fail all at the same time.

Don't change valves unless there's evidence they aren't performing as well as they did. If you're not sure, swap in some spares and see if anything improves. It's always a good idea to have spares - at least, a preamp valve of each of the types your amp takes, a set of power valves, and a rectifier valve if it has one.

New power valves may need the amp bias checking and/or adjusting, preamp and rectifier valves don't.

martinw

ICBM said:

Don't change valves unless there's evidence they aren't performing as well as they did.

I agree with all of the above, and mostly this bit, except that I'd say that in some amps that use EL84s my advice would be to change them periodically to prevent failure in use. The period depends on the amp type and usage e.g. I know of well-used AC30s that have a new set every 3-6 months.

IMO if you wait until you can hear a deterioration with these (hard because it happens gradually anyway) then you risk one packing up mid-gig.

 

57Deluxe

Think of valves as Medieval Alchemy.... that is as much guarantee you'll ever get...

Budwiser

when it comes to valve changing two factor's crop up..(1) how hard are they being used say 6hr of more per day then they will need changing say 8..months some may last years if having light usage. pre-amp valve's have a easy life has there not driven has hard as the poor power valve's.  plus there's the added tech job of setting them up right for correct usage..yes there's diy video clip's that make it look easy that's because a good tech as passed the information on.  

I've seen el34's with burnt bases and slight melted outer glass casing due to running way over there spec.. I once heard a guitar say 'yeah, I just crank the bias pot till the amp sound right!!  mmm smell them valve's burn..red plating the power valves is the quick's way to roast the valves..

Peavey 5150 fixed biased circuit you simply pop the knackered valves out and check there 100 ohm 5w resistors for o/c fault..

happy trails...

Budwiser

'.I once heard a guitar tech say 'yeah, I just crank the bias pot till the amp sound right!!  mmm smell them valve's burn..red plating the power valves is the quick's way to roast the valves....