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PostPosted: Tue Apr 19, 2011 5:10 pm 
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Mark II

Joined: Sat Jun 14, 2008 1:38 am
Posts: 52
Location: SF Bay Area
Quick question about microphonic tubes:

If you push and otherwise quiet tube to the point of squealing, does it damage the tube or make it more prone to be microphonic - or can you just back off and it returns to "normal".?

Thanks,
Ron


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PostPosted: Tue Apr 19, 2011 5:27 pm 
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Dual Recto

Joined: Mon Jul 16, 2007 1:01 am
Posts: 2828
Location: SoCal
It may or may not have been microphonic all along. Most will return to "normal" when the gain and/or treble is reduced. In my experience, a tube is either microphonic or not, and some have a higher threshold, but I doubt a perfectly good tube would be damaged by injudiciously cranking everything to "10".
I did just that, once. I turned every knob on my Mark III up to "10", all knobs pulled out, then took it off standby. Nothing plugged into the input, by the way.
Squealed like the proverbial porcine quadruped.
Worked just fine after I surprisingly regained my sanity.


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PostPosted: Wed Apr 27, 2011 10:10 pm 
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Single Recto

Joined: Sun Feb 19, 2006 11:43 am
Posts: 1459
Location: NYC
All preamp tubes are microphonic to some degree.What you did was prove that point.You turned it up loud enough to hear the microphonic quality.Just turn it back down.If it gets to the point that you cant turn it up enough to get a good tone,then the tube is "too" microphonic for that amp.But dont discard it.Many tubes that are too microphonic for a high gain circuit are perfectly usable in a lower gain amp such as a Fender.Most preamp tube failures are the result of becoming too microphonic,you probably didnt hurt the tube and as long as you can get a good tone with that tube,it is still good.


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PostPosted: Fri May 13, 2011 4:02 pm 
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Mark II
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Joined: Sat Aug 21, 2010 12:15 pm
Posts: 116
what about a tube that i install, then have to tap on to have it "come to life".

it's a baldwin sylvania 9 hole on the plate...and it sounds like heaven..but i have to reach in almost every time to tap it to life....and even then, sometimes it takes 5 minutes to warm up enough to where i can even hear it when im tapping.


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PostPosted: Fri May 13, 2011 6:01 pm 
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Single Recto

Joined: Sun Feb 19, 2006 11:43 am
Posts: 1459
Location: NYC
Sounds like you have a faulty connection,probably in the heater.Does it appear that the tube does not light up till you tap it?If so,it is the heater.If the tube is lit before you tap it then there is another loose connection in the tube.Of course if you get the same symptom with any other tube in that socket,the problem is likely in the socket.


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PostPosted: Fri May 13, 2011 9:43 pm 
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Mark II
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Joined: Sat Aug 21, 2010 12:15 pm
Posts: 116
yeah
it lights up, but i still have to tap it.

other tubes work fine, so im pretty sure the socket is stable.

i can use it at home and for recording in v1 or v3....but i won't roll the dice at a gig as the RFT i have in there now sounds perfect too..just different perfect!


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