Valve trouble question

[tim1750]

Hi all, I have a question about output/power valves, if my output valves still hold bias voltage steady with plenty of gain left on the pot's does that mean that my valves are still good ?, The reason I ask is because I'm getting a difference in sound from the left channel with the sound going dull in the highs then rising back up to where it should be and I don't know if it's time to re-valve, I'm a little reluctant to buy more valves as I have only had the valves about 4 years .
Forgot to say that all the valves in the amp look just fine with no visible blue gases
Any suggestions would be greatly received
Many thanks in advance
Tim

[Ali Tait]

Not necessarily. Swap the output valves to the other channel, see if the problem with the sound follows the valves.

4 years in what I'm assuming is a PP amp could easily mean they need replaced, that's a fair amount of hours.

[tim1750]

Cool,thanks for your help Ali i'll give that a try and see what happens mate.

[Firebottle]

A good suggestion from Ali :thumbsup:

If you valves are holding their bias steadily and the gain is as was I would hazard a guess that they are OK.

:)

[Ali Tait]

No worries, let us know how you get on.

[nthall]

4 years is a pretty good lifespan for valves in an amp that gets regular use.

[Barry]

The typical lifetime for an audio power valve is 10,000 hours (though some may have lifetimes exceeding 50,000 hours).

Assuming you use your amplifier for 5 hours a day, the valves should last at least 5 years. Overbiasing the valves can shorten the life.

Some enthusiasts replace the valves once a year as a matter of course.

[nthall]

I tend to like them under-biased in push-pull. That's probably even worse for them.

[tim1750]

Hi All, Thanks for all your advice but I think I must have had a loose or dirty connection Because I swapped the valves around and put them back to were they came from now I don't hear any problems at all.
So thanks again
All the best
Tim

[CornishPasty]

I do think some of us change valves more often than is necessary. This may be borne out of the desire to do some "tube rolling" but personally I find it unnecessary. I've only ever replaced one set of valves due to ageing in twenty years of ownership of valve equipment and that was more because the amp was second hand and full of cheap unbranded Chinese valves. I usually give my kit a check over once a year, giving the thing a hoover out, cleaning the valve pins and holders and rebiasing where necessary. I'm fortunate that I have a rudimentary valve tester but I only use it when I feel there's something not sounding quite right and some further investigation is required. Apart from that I just get on with the business of listening to the music :)

[Ali Tait]

Hi All, Thanks for all your advice but I think I must have had a loose or dirty connection Because I swapped the valves around and put them back to were they came from now I don't hear any problems at all.
So thanks again
All the best
Tim

Good news. It's a good idea to keep valve pins clean. This sounds daft but it works. Stand your valves up in a saucer, fill with Cola Cola up to the top of the pins and leave for a couple of hours then remove, clean and dry. Works a treat.