New valves; now what?

Toast

So I've ordered a new set of valves (JJs) for my Peavy Classic 50, but I know NOTHING about how to fit them.

So please guys, help me with the do's and don'ts of replacing valves.

PS: the PC50 does not have to be biased, so luckily I can skip that.

AlanRatcliffe

Simple. Yank out the old ones and push the new ones in. A slight "rolling" motion helps and when fitting new tubes I normally clean the pins and sockets with contact cleaner and fit the tubes into the sockets and pull them two or three times to make sure they make good contact (especially with NOS tubes, where the pins can have a little oxidisation on them).

MIKA-the-better-one

Dont hold the power tubes with your fingers, rather use tissue or somehting for a barrier between....
I dont know why but I know you must do this....

Dont stress to much they are pretty simple..... or maybe someone who lives near you from the forum can help you??? I was lucky enough to get a coach the first change

needleshy

a rebias may be in order if you are replacing power tubes.

Toast

Thanks guys!

One more question: which contact cleaner is safest to use?

ezietsman

needleshy wrote: a rebias may be in order if you are replacing power tubes.

Peavey Classic 50 is non-adjustable fixed bias. Just pop in and go, you cannot (without effort) change the biasing.

Toast

New valves are in; sounds great! The JJs have made the OD channel just a bit brighter than it used to be and that is exactly what I wanted. ?

BUT, after about 20min of playing the fuse of the amp blew. First time this has happened in 5 years. Any ideas why?
I replaced the 2A, 250V fuse with a 3A, 250V and everything seems fine. Is this OK? :-[

Norman86

MIKA the better one wrote: Dont hold the power tubes with your fingers, rather use tissue or somehting for a barrier between....
I dont know why but I know you must do this....

Dont stress to much they are pretty simple..... or maybe someone who lives near you from the forum can help you??? I was lucky enough to get a coach the first change

Mika, the reason is so that you dont decrease the life of the tubes!
by putting your bare fingers on the valve, you put oils and dirt on it, and because it works at such high temps, it can cause premature failure!

I have a few lamps that work at such high temps, its the same principle as valves ?

MIKA-the-better-one

There we go.. now we know.... Dont use your fingertips

Gearhead

Pure and utter nonsense. The story about the burning in of greasy acidy stuff on your fingers comes from halogen lamps that operate at 100+degrees. At high temperature the stuff carbonises, making it black. It then absorbs light from the lamp, whereas the rest of the bulb does not, which creates thermal tension which breaks the glass.
Firstly the tube does not run at that temperature (and if it does don't worry about breaking it, it will burn out quickly), secondly it does not emit more than a few candela of light so there is no extra heating of certain spots and thirdly the glass of a vacuum tube is way thicker than the gas filled envelope of a halogen lamp.
If you are worried about smear on a tube, either never buy NOS tubes (imagine how many people touched it, yuck, leave them for us) or clean with acetone religiously before mounting.

makepeace

thanked.. i was wondering about it. it seemed a bit irrational to me when i read an article about it.

Norman86

At what temps do the valves then run at?
Just curiosity!!
Thanks!

Karel-Mars

I've read specifications that say temperature should not exceed 250 deg C anywhere on the glass, so I guess you can expect at least 200 deg C after a balls to the wall jam :yup: Enough to put a blister on your little finger, maybe a blister on your thumb.

Norman86

Thats the way you do it ?

Thanks Karel!