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Broken tube on Art Audio Carissa 825 amp

I have neglected my main audio system for a while - once I figured out that I really couldn't tell the difference between a $600 power cord or speaker cable and the ones that came with the equipment, I somehow lost the urge to keep "improving" it. :-o

I decided it was time to dust off the equipment and get it working again - I do still love to listen to music even if I do apparently have a tin ear - but discovered one of the tubes on my amp has broken. I am thinking my cat was the culprit but I really don't know. The broken tube is a Ei 12BH7 (Yugoslavia.) Do I need to replace it with the exact same brand and model of tube or is there a better one to try? If I replace the tube with something different, is it best to replace the similar tube on the other side with the same thing?

Also, I have been out of the game for a while; please recommend some good places to purchase tubes.

Of perhaps more concern is that some of the glass from the broken tube has fallen down inside of the amp - should I panic? I tried to remove some of the broken bits with a pair of hemostats but only managed to push it down into the guts... DOH! Other than taking the amp apart - which I am most reluctant to do, for obvious reasons, and not even sure if I Can do it- I am not sure how to remove the glass bits. :-(

Holly
oakiris
bill_k
915 posts
 
Holly,
Regarding the broken 12BH7 tube, first I would try to remove any more of the broken tube bits left in the amp. Have you tried holding the amp upside down and seeing if you can get any more broken pieces to fall out? I know that the amp is heavy but that may be your best shot at removing the remaining pieces short of opening up the case for surgery. If the broken bits are just glass you'll probably be ok, but if there's any metal then you could have a short that could cause extensive damage if you power it up. Do so at your own risk! As far as replacing the tube, I would strongly suggest that you replace that tube in both channels so that they have a matching tube complement. Otherwise the two stereo channels may have a difference in sound quality. You do not need to get the same brand of tube, just 12BH7 tubes or equivalents should do fine. The Tube Store is known to be a reputable supplier, and they currently show three choices of that tube type being available. Best of luck and let us know how it goes!
jeffreyds
115 posts
 
I can't help with how to extract the tube pieces from the amp, but I found that swapping out the 12BH7 tubes with NOS RCA's on my Carissa made a dramatic improvement. Make sure you replace both.
oakiris OP
206 posts
 
Sorry I haven't responded before now; this thread got lost in the shuffle! lol And I see I put 825 in the title - the amp has 845 tubes, not 825's, which I don't think exist!

That was a good suggestion, Bill, but there is no way that I can hold the amp upside down - it weighs at least 70 pounds and I can barely lift it from the shelf it is on, let alone holding it upside down and maybe shaking it gently to get more loose glass out of it. Anyway, I contacted the manufacturer and they said not to worry about the broken bits of glass that are inside the amp, they will do no harm. Luckily, it is just the glass that fell down inside, no metal bits. They also said both of the 12BH7's needed to be replaced as these are the driver tubes.

I ended up getting a matched pair of EH (Electro-Harmonix) 12BH7 tubes for the amp. I imagine NOS RCA's would sound nicer, but the price for these EH tubes was a much closer match to what I could afford, and they work just fine. My amp is back in business and I am happy!

Holly
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