Recycling tubes

[Eric]

Tony Allgood wrote:
> 
> Hi folks,
> 
> A little while ago I asked the list about information about valve
> amplifiers. I am thinking of doing a valve project, perhaps a pre-amp.

>If I
> have some old valve amps, can I use the tubes inside?

Yes, if they have not been used up in the past. Tube cathodes are only
used up when operating. 

> I know they don't last
> forever, how can I test if they are alright?

You would need a tube tester. If you or a friend don't have one,
try an older local electronics dealer.

It would be MUCH easier to buy fresh tubes. In the UK, Billington
Export Ltd. and Maplin sell audio valves. They also have all other
parts needed, plus books on building tube audio equipment.


> I read somewhere that hum will
> increase as a valve amp gets older, is this true?

Because the filter capacitors are going bad. Not because the tubes
are bad. Electrolytic caps over 20-30 years old should ALWAYS be 
replaced, especially in valve equipment.

If you need more help, look at http://www.svetlana.com--it has
data on all the Svetlana types, plus technical bulletins showing
how to use them, plus a list of distributors.Also see
http://www.vacuumtube.com
and http://www.duncan.simpleamps.com for info and links.
And try the Engineering Musician website. Use a search engine
to get the URL.