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are my tubes going old?

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El Chiguete:
How do I know that I need to change the tubes? I've never player thru a set of tubes in a piece of gear that I've own so I don't know how to know if its going microphonic or just good time to replace them? Any advises from experience?

MarshallJMP:
Usually you will hear it when you replaced the tubes.The problem is that the decay is so slow your ears get used to it and you won't notice it untill you put in a fresh pair.

El Chiguete:
Good point.

MarshallJMP:
Some signs of decay are loss of bass and highs

rnolan:
Valve Article (attached) gives some good insights.  Modern tubes don't last as long as the old ones (not pumped as much).  This suites the OEM market so they can sell you new tubes (Boogie, Marshall etc) and the OEM market is by far the biggest consumer of tubes (this is good in some ways as we can then buy some...).  As MJMP says, they go down slow so you don't notice.  For MP1 ADA recommended tube change every 2 years (BTW very dependent on use).  I found the original Chinese bottles ADA used lasted much longer that 2 years even with high gain/high use (min 5 days a week).  In the MP2 (IIRC) they recommend 6 month tube change, again I was happy for much much longer.  MJMP changes his 3TM tubes every 3 to 4 months to keep the sound how he likes it (some would say a bit pedantic, not me though, I totally understand).

So seems the MP2 chews tubes faster than the MP1 (according to ADA), again depends on how you play (high gain settings etc) and how often, in my experience, they don't tend to get more microphonic over time, just loose some definition/sparkle get a bit muddy, bit like guitar strings (but much slower), BTW some people like their tubes old/dullish.

The up side is that input tubes (e.g. 12AX7s) are not outrageously expensive (~$20) so you can afford to routinely change them out and also experiment with various offerings, BTW I just had some good feedback in another post here re these tubes (http://www.dougstubes.com/preamp-tubes/12ax7-ecc83-7025/mullard-cv4004-12ax7.html), hey MJMP, I recon these (short plate Mullards) would go well in a 3TM.

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