# Tube amp questions



## Diablo (Dec 20, 2007)

Wondering if anyone can point me in the right direction in terms of my amp (CAA OD-100).
1) the amp is sounding a little flat to me lately, lacking some gain, might be my ears or could it be old tubes? How often do you change them?
2) current power tubes are marked Sovtek 5881/6l6 ....so what do I replace them with, 5881's or 6l6's?
3) are tubes date stamped? Mine seem to be marked 08 01, so maybe August 01? Amp is a 2005 model yr.
4)do you normally replace the preamp tubes as well
5) can I just plug in new tubes or is biasing required, and if so, should I farm that out to a pro?

thanks in advance!


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## Wild Bill (May 3, 2006)

Diablo said:


> Wondering if anyone can point me in the right direction in terms of my amp (CAA OD-100).
> 1) the amp is sounding a little flat to me lately, lacking some gain, might be my ears or could it be old tubes? How often do you change them?
> 2) current power tubes are marked Sovtek 5881/6l6 ....so what do I replace them with, 5881's or 6l6's?
> 3) are tubes date stamped? Mine seem to be marked 08 01, so maybe August 01? Amp is a 2005 model yr.
> ...


Preamp tubes can last for years! I've pulled them out of old gear 50 years old and they still work great! They can and do fail, of course. Still, they need replacement nowhere near as often as power tubes.

Power tubes handle big gobs of current, which wears them out much faster.. What's more, modern tubes don't seem to last as long as tubes did in the Golden Years. An amp that is gigged everyday might give them a year or so. One that only gets played on weekends might have them last 5 years or more.

5881s sold today are just 6L6s with a different number marked on them. Originally they were an industrial number for a tube of slightly less power with otherwise identical characteristics.

This is why techs have tube testers! I must have collected a half dozen of those over the years. No tech should be without one.

Your guess about date codes is quite correct.

I covered preamp tubes. Only replace if they test bad.

Nowadays with modern tubes not always being made very close to specs you really have to check the bias after every replacement and if necessary reset. If bias is setting the idle current too low, you get a thin tone with less power. If it sets things too high the tubes may run too hot and burn themselves out early. In extreme cases that can mean VERY early!

Besides, when a tech is checking the bias it is also a great opportunity to inspect the amp while it is opened up, making sure the main voltage points are in the ball park and that there are no signs of things burning up!

Some modern amps bring the bias test points outside the chassis, so that you don't have to open up the amp to do the job. Me, I like to open things up anyway! Otherwise there is never any routine inspection done until something blows up. Opening up the amp is not that big a deal and well worth it, in my opinion. It's like how a good car mechanic will give the underbelly of your car a lookover while it is on his hoist for an oil change, just too make sure nothing is falling off.

Hope this helps!

Wild Bill/Busen Amps


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## Diablo (Dec 20, 2007)

Thanks Bill.
As per our PM, I'll bring it in to you. I figure its due for a once over anyways. Its a keeper


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## jb welder (Sep 14, 2010)

Wild Bill said:


> 5881s sold today are just 6L6s with a different number marked on them. Originally they were an industrial number for a tube of slightly less power with otherwise identical characteristics.


 That's what I thought too! Till I saw these: www.thetubestore.com - Tung-Sol 5881 Audio Tubes At least this vendor is warning people, I've seen other sellers who don't seem to realize they are not the same as regular 6L6's So now to further confound things we have re-issued 5881 "Tung-Sol's" that are only 23watts and can only take 400 plate volts. So the Sovtek tubes marked 5881WXT or 5881/6L6WGC can be used as regular 6L6GC replacements, but the new Tung-Sol 5881 reissues are only suitable where original old style lower power 5881's were used. Just found this out recently so I thought it would be good to let ya'll know.


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## Wild Bill (May 3, 2006)

jb welder said:


> That's what I thought too! Till I saw these: www.thetubestore.com - Tung-Sol 5881 Audio Tubes At least this vendor is warning people, I've seen other sellers who don't seem to realize they are not the same as regular 6L6's So now to further confound things we have re-issued 5881 "Tung-Sol's" that are only 23watts and can only take 400 plate volts. So the Sovtek tubes marked 5881WXT or 5881/6L6WGC can be used as regular 6L6GC replacements, but the new Tung-Sol 5881 reissues are only suitable where original old style lower power 5881's were used. Just found this out recently so I thought it would be good to let ya'll know.


Thanks, JB! It seems there are some differences in the marketplace that are important to notice. I knew the original 5881s were only 23w Pd but I wasn't aware that anyone was making them like the originals today.

It figures that it was TungSol who went the extra mile to faithfully copy to the old specs! That is what they did when they started making their 12AX7s. Like the ones made in the Golden Years, they took a bit more trouble with the heaters so that they had the lowest possible hum factor. Also, they do not like to be placed in sockets where the designer flogged the hell outta them for extra gain, instead of using an extra tube. That's why in amps like Carvin and Boogies if you use a TungSol in the 1st position you can end up with squeals and howls. I have a Mesa tech service bulletin somewhere in my files warning techs to use only Mesa preamp tubes. Since Mesa tubes are usually just rebranded Chinese, which tend to have a bit less gain than the data sheets, this makes sense, in an ironic way. Boogie also pushs the 1st tube for excessive gain, so they have to use a tube with less gain to keep it from becoming unstable! 3 steps forward and 2 back, I guess.

I will watch out for this in the future! Thanks again for the tip!

Wild Bill/Busen Amps


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## nonreverb (Sep 19, 2006)

As discussed in another post, There's evidence that the "new" 5881 isn't up to par in comparison to the old ones. Just 'cause it looks like one, smells like one, does not make it one...Sovtek is doing a good job but it still has a ways to go before it can claim their tubes are the "same" as the old Tung Sol offering IMO.



Wild Bill said:


> Thanks, JB! It seems there are some differences in the marketplace that are important to notice. I knew the original 5881s were only 23w Pd but I wasn't aware that anyone was making them like the originals today.
> 
> It figures that it was TungSol who went the extra mile to faithfully copy to the old specs! That is what they did when they started making their 12AX7s. Like the ones made in the Golden Years, they took a bit more trouble with the heaters so that they had the lowest possible hum factor. Also, they do not like to be placed in sockets where the designer flogged the hell outta them for extra gain, instead of using an extra tube. That's why in amps like Carvin and Boogies if you use a TungSol in the 1st position you can end up with squeals and howls. I have a Mesa tech service bulletin somewhere in my files warning techs to use only Mesa preamp tubes. Since Mesa tubes are usually just rebranded Chinese, which tend to have a bit less gain than the data sheets, this makes sense, in an ironic way. Boogie also pushs the 1st tube for excessive gain, so they have to use a tube with less gain to keep it from becoming unstable! 3 steps forward and 2 back, I guess.
> 
> ...


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## Wild Bill (May 3, 2006)

nonreverb said:


> As discussed in another post, There's evidence that the "new" 5881 isn't up to par in comparison to the old ones. Just 'cause it looks like one, smells like one, does not make it one...Sovtek is doing a good job but it still has a ways to go before it can claim their tubes are the "same" as the old Tung Sol offering IMO.


So TungSol is really Sovtek? That explains a lot! hwopv

Wild Bill/Busen Amps


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## WCGill (Mar 27, 2009)

As are Mullard, Genalex Gold Lion and Svetlana.


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## dtsaudio (Apr 15, 2009)

Tung-Sol, Electroharmonix, Mullard (re-issues), Sovtek, and Svetlana (KT88's and 6550's) are all made in Sovtek's Reflektor plant. The US distributor New Sensor owns all these brands. That's not to say there aren't differences in the brands. They all have their own characteristics, but they're are similarities as well.


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## nonreverb (Sep 19, 2006)

You can thank Mike Matthews. He bought the rights to the names of defunct tube manufacturers Tung Sol and Mullard and Genalex. I suspect he was gambling on the fact that most understand these names to be synonymous with quality. Too bad that they don't compare to what was produced by the original manufacturers.


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