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RE: Tube strength and readings

Posted by sony6060 (A) on September 7, 2014 at 17:30:41

In Reply to: Tube strength and readings posted by Maddnotez@gmail.com on September 7, 2014 at 16:59:56:

Info like that on ebay is all over the place from a technical stand-point.

The 12AX7 has a center design target of 1600gm. Some NOS 12AX7s measure 2000gm. Thus, a real 1250gm measurement may be a highly used tube. An exception are some new manufacture tubes such as the Sovtek 12AX7LPS that is normally 1250gm.

A life test that reduces the vintage 12AX7 filament from 6.3 volts to 5 volts is a better indicator of tube health. At 5 volts, a 12AX7 healthy tube will not drop test readings at all where as tubes with little life left will drop at least 5-10% or more. However, no one wants you to know about that test on used tubes on ebay.

So, buyer beware.

Edit- some NOS tubes such as 6AQ8 and some 6922 drop like a rock at 5 volts filament. Thus, I am referring to 12AX7s above. It takes time testing tubes to get a feel of this life test.

Edits: 09/07/14 09/07/14

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