Suffering Heath
47 posts
Apr 14, 2014
7:57 AM
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Question for the Elders of the Forum:
When one turns off their amp, how much time should elapse before it's safe to pull the pre-amp tube and stick in another tube?
Thank you!
Heath
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http://www.reverbnation.com/thebluesprofessors
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5F6H
1762 posts
Apr 14, 2014
9:06 AM
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As soon as the tube is cool enough to be removed without burning yourself. Preamp tubes don't often get very hot, but don't take advice from me, I have no fingerprints...12AT7 in Fender reverb circuits get very hot!
Most preamp tube sockets have a skirt so that you can't touch a plate pin, whilst it is still in the socket, you can't get a shock if you hold the cool bulb of the tube.
Power tubes get very, very hot...some places sell gloves for handling them...10-15mins is usually enough to let them cool...unless you are in a particular hurry to burn yourself.
By the way "off" means both power & standby...not just on standby (tubes are still getting high current AC from the heaters). Best to unplug from the wall before removing anything.
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jpmcbride
46 posts
Apr 14, 2014
11:00 AM
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Just to add to what 5F6H said ...
Its not just "best" to unplug the amp, its ESSENTIAL!
When the amp is off there is still high voltage somewhere inside the amp. Always unplug.
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Jim McBride
www.bottleoblues.com
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rockmonkeyguitars
60 posts
Apr 14, 2014
11:33 AM
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^depending on the the amp, there is still high voltage (enough to kill you) even when the amp is unplugged. I do agree that it is essential to unplug the amp before a valve swap. I once pulled a valve on a super reverb while it was still plugged in blew my house's 10amp fuse.
Like the others said, as long as the amp is unplugged, you can pull a tube as soon as it's cool enough to touch. If you wear gloves, you can pull it as soon as you unplug your amp.
Last Edited by rockmonkeyguitars on Apr 14, 2014 11:34 AM
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Barley Nectar
356 posts
Apr 14, 2014
4:30 PM
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NEVER get your hand down by the pins when pulling tubes. Yes, there is still deadly voltage in that amp even with it unplugged. Grasp the glass bulb and gently rock the tube while applying a steady pull...BN
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6SN7
437 posts
Apr 14, 2014
5:34 PM
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UNPLUG YOUR AMP BEFORE REMOVING ANY TUBES.
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Greg Heumann
2684 posts
Apr 15, 2014
8:34 AM
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UNPLUGGING YOUR AMP DOESN'T ELIMINATE THE RISK!!!
First, the accessible (tube) side of the chassis doesn't pose any risk unless you can stick your finger inside a tube socket where the voltage is. Glass and plastic are not conductive; the chassis itself is (or should be) grounded. The power tubes are big enough that you could conceivably contact the pins while you were pulling it out, while they were still connected to the socket - but you'd have to work at it. So just wait for them to cool down and go ahead.
But it needs to be really clear. UNPLUGGING YOUR AMP DOESN'T ELIMINATE THE RISK!!!
If you work on the INSIDE of the chase then there is a real risk, and unplugging the amp doesn't eliminate it, nor does waiting a few minutes. The power filter capacitors can hold their charge of several hundreds volts for DAYS. You should always discharge them before working on the inside of an amp.
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***************************************************
/Greg
BlowsMeAway Productions
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Last Edited by Greg Heumann on Apr 15, 2014 8:36 AM
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