Most of the criteria listed for tubes from online resellers is nonsense.
The 12AX7 is a popular audio preamp tube, so anything people can imagine
makes a difference like the shape of the getter or the color of the plate
will be used to try to eek more value out of the sale.
When replacing tubes, especially in Tek scopes, any tube of the correct
type will do EXCEPT when specific matching criteria are prescribed by Tek.
Any tubes that need to be matched or "selected" for a given parameter will
be called out in the manual with a specific part number (the description
will say something like "Tube, 12AX7, selected". There is a document on the
tekwiki that will provide the selection criteria (e.g. that the two
sections of the tube are matched within x percent). If you're just trying
to get the scope running, selected tubes aren't as important. They matter
much more when you're trying to achieve calibration or meet the original
performance specs for the scope.
Dave Casey
On Fri, Aug 30, 2019, 2:10 PM Jamie Ostrowski <jamie.ostrowski@...>
wrote:
When a tube needs to be replaced in an oscilloscope, will matching the
tube number be sufficient, or are there other items to consider about the
tubes? For example, if I have a bad 12AX7, will any 12AX7 do, or do I have
to get one with the matching D-getter, the right plate color, etc, etc. I
look online for a 12AX7, and there are a multitude of variants listed.
