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Post subject: A general tube question
Posted: Tue Dec 08, 2009 6:59 am
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I'm getting a used tube amp with two power and three preamp tubes this weekend. Are tubes generally like light bulbs, where if they are working they are working, or do they degrade a little with time and still keep working, but not like when they were new? I'm asking becuase I would change them to get the amp to a newer state. Thanks for any replies.


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Posted: Tue Dec 08, 2009 7:36 am
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Normally, tubes slowly wear out and the amp doesn't seem to sound as good as it once did. Power tubes generally wear out faster than pre-amp tubes. But, I believe that what seems to be a good tube can also go bad quickly. There's nothing wrong with putting new tubes in your amp when you get it. Try it out first; if the amp sounds okay, then you can use the old tubes as spares. (You should always have spare tubes!) And, sometimes new tubes can be bad!

In case you don't know... most amps need to have the bias checked when replacing power tubes. Find out if your amp needs to be biased, and take it to an amp tech if you don't know how to do it yourself. Pre-amp tubes can be swapped without biasing.


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Posted: Tue Dec 08, 2009 7:49 am
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Just to add to what was said a tube can appear to look good with its heater all glowing, and be deader than a doornail :)

If the tubes are all glowing and the amp is not sounding or sounding real bad it may need some tube swaps.

Trivia: a power tube really blowing can occasionally take other components down with it, most commonly the fuse but other things may cook too.


If an amp can be biased, it should be done periodically even if the power tubes are not being changed, they then to drift over time. Also some amps are "fixed bias" (Blues Junior is one I believe) and bias cannot easily be changed without soldering new components into them.

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Posted: Tue Dec 08, 2009 8:09 am
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The amp is a two year old Blues Deluxe Reissue. Does this one need to be rebiased to change power tubes or is it fixed bias?


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Posted: Tue Dec 08, 2009 10:23 am
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Blues Deluxe RI uses 2 6L6 tubes for the power stage, and yes it does need an occasional re-bias, especially if changing to a different tube pair.
(power tubes need to be changed in matched pairs.)

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Posted: Sat Dec 12, 2009 8:26 am
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I would always replace the tubes right away in a used amp. Especially if you are playing gigs with it and want to avoid trouble at the worst possible time.

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Post subject: tubes
Posted: Sun Dec 13, 2009 9:02 am
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one thing i used to do with tube equipment is remove the power tubes and look at the circle of mercury on side of the glass.if theres brown rainbows surronding the mercury or, if the whole mercury turned brown i knew it was time for replacement reguardless.


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Posted: Sun Dec 13, 2009 1:19 pm
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This is going to sound dumb, but where do I find the mecrcury strip?


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Post subject: Re: tubes
Posted: Sun Dec 13, 2009 6:57 pm
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davededude wrote:
one thing i used to do with tube equipment is remove the power tubes and look at the circle of mercury on side of the glass.if theres brown rainbows surronding the mercury or, if the whole mercury turned brown i knew it was time for replacement reguardless.


That's not entirely true. It called getter flashing. It's not Mercury it's Barium atoms that firm the mirror.

Here's some interesting information. I opened my eyes too because I thought the same thing.


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Posted: Fri Dec 18, 2009 1:02 am
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hi fossilman. your fender deluxe amps tubes are available at your nearest fender shop. you can get a matched set of output tubes. ie. groove tubes color coded pear. they are fitted from new in your amp. so if you get the same type they don.t need to be re. biased. please note before you get inside any amp all amps contain lethal voltages .these can be present at fuse points. tube sockets. and all sorts of places you don.t think of as being life.threatening. power supplies can store a fatal charge for days if not discharged properly hope this is not to much to take just be safe. and enjoy the wonderful world of amps. :) cheers.


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Posted: Fri Dec 18, 2009 5:08 am
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i havent opened up one of these amps in a very long time i dont know if now they have bleed off resistors on the power supply filter caps now. also. i stand corrected on the baruim flash on side of tube. i look at the flash and if it is very discolored, i know the tube has been beaten on or circuit /bias probs caused it to run hot. i never said they would be dead but, i see that then after checking curcuit out i replace them thats all.


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Posted: Fri Dec 18, 2009 5:13 am
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btw..i have had power tubes with the barium burned completely off and still show up around 80 to 120 on my transconductance tube tester. those i usually put aside for other purposes.


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Posted: Fri Dec 18, 2009 6:22 am
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cliff.lee wrote:
hi fossilman. your fender deluxe amps tubes are available at your nearest fender shop. you can get a matched set of output tubes. ie. groove tubes color coded pear. they are fitted from new in your amp. so if you get the same type they don.t need to be re. biased. please note before you get inside any amp all amps contain lethal voltages .these can be present at fuse points. tube sockets. and all sorts of places you don.t think of as being life.threatening. power supplies can store a fatal charge for days if not discharged properly hope this is not to much to take just be safe. and enjoy the wonderful world of amps. :) cheers.


The bias should ALWAYS be checked when you replace the power tubes. GT's would be the last thing I'd use. They're way overpriced and there are much better tubes out there for a lot less money. Fender uses GT's because they Own GT's.


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Posted: Fri Dec 18, 2009 7:37 am
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Fossilman wrote:
The amp is a two year old Blues Deluxe Reissue. Does this one need to be rebiased to change power tubes or is it fixed bias?


What do you think that fixed bias means you don't have to check and bias the amp?

Take it to a pro!!!! You need to learn the difference between fixed and cathode Especially if you are changing tube brands.

Trivia most Fender's are biased on the cold side, Colder the worst the tone and too hot will burn up the tubes. Most times you can heat them up for better sound.

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Posted: Fri Dec 18, 2009 8:32 am
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cvilleira wrote:
Fossilman wrote:
The amp is a two year old Blues Deluxe Reissue. Does this one need to be rebiased to change power tubes or is it fixed bias?


What do you think that fixed bias means you don't have to check and bias the amp?

Take it to a pro!!!! You need to learn the difference between fixed and cathode Especially if you are changing tube brands.

Trivia most Fender's are biased on the cold side, Colder the worst the tone and too hot will burn up the tubes. Most times you can heat them up for better sound.


+100 Seriously. Fender sets the bias cold so the Groove Tubes last longer. They bias at something like 62mv. Dump the GT's, throw in some JJ's and bias to around 80-85mv. It'll be like a new amp. If you bias GT's that high, they;ll go up in smoke in a few months.


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