How to tell what valve needs replacing?

[Lewkk]

Hi, I was playing my Cornford earlier and the bottom end and a heap of volume cut out, it sounds like a transistor amp now :P

Im praying it's just in need of a valve change (it's not had one for years :NUTS).

Are there any quick tests to figure which valve needs replacing ... or on second thoughts perhaps I should stop being a cheap bastardd and replace them all

Thanks

Lew

[Old Tele man]

...plug in a "new" set of same-type tubes, if sound 'improves,' then (obviously) the "old" tubes were worn-out, if not, continue using the new set and keep the old set as spares.

...it's called the "rotate & compare" method and works great when you start with a set of matched quad tubes (ask Blue Strat for more info)

[Brien]

Get yourself a backup set of tubes anyway. Pop them in one by one (for preamp tubes) to find the problem. There is no reason to assume that all of your tubes are bad. I would replace power tubes in sets usually, depending on what type of amp, cathode bias, wear on tubes, etc.. Based on what you're saying, I'd bet it's the power tubes or the 1st preamp tube.

[Macaroni]

Change your Rectifier and Phase Inverter first, to rule them out off the top. then start with the preamp or power tubes.

[dk123123dk]

I would get another set of MATCHED power tubes. Depending on what type of amp you have, you may need to have the amp biased. Try that. If that doesn't work, you should get a good NOS preamp tube. Most amps use 12ax7's in the preamp. You can try the new tube in different spots. This tube will give you a better sound if you have stock tubes in the amp. You might want to check with the manufacturer for details regarding the bias. Good luck!

dk

[Lewkk]

I will order a set after christmas then.
It is a hurricane and uses el84s I believe.

Ta