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Old 11th Jan 2010, 10:03 am   #55
GrimJosef
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Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Homebrew Valve Tester

Quote:
Originally Posted by AmadeusMozart View Post
It is always best to test a tube in a setting which is close to its intended use.
This is SO true, especially with the larger and more expensive valves.

Quote:
Originally Posted by swordholder View Post
The tester will supply 250v @100mA OK, the current is limited to about 110mA. The transformer shows no sign of stress as it is only used for a short period of time.
25W should be OK for most valves. But the reason for running at high power is so that the internal metalwork and, to some extent, the glass envelope can get properly hot. This takes at least a couple of minutes.

A useful feature, if it's available, is the ability to run at high power for many hours. This can be an effective way of rescuing gassy valves. I've had about a 50% success rate with vintage KT66s. Since each one goes from being worth <£10 as a dead display item to >£50 as a working valve it can very quickly pay for a high current transformer. However I do realise that this is not what more than 90% of the unit's users will be doing with it. So if it would seriously increase the price then I'd say it probably isn't justified.

Cheers,

GJ
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