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Rectifier tube keeps blowing

I have a cheap Chinese tube amp. It uses a 274B rectifier tube from Valve Art. Once during listening, the rectifier tube blew and so did the fuse. I replaced the fuse and replaced the rectifier with another 274B from Valve Art. Then, days later, I turned the amp on and same thing happened at power up. Fuse blew, rectifier went. I changed the fuse again and added my third (and last) rectifier tube. Every time I turn the amp on now, I take a deep breath and turn my head. What the hell is going on here? I think a rectifier turns AC to DC (dangerous). If the rectifier goes, than damage could occur to the transformers,tubes or the whole amp could take a dump. I just put some great KT77's in here and I don't want anything bad to happen. Is it the Valve Art tube? Is it shoddy workmanship in a cheap Chinese amp? Help.
devilboy
atmasphere's avatar
atmasphere
11,800 posts
 
I would not be surprised to find a bad filter capacitor in the power supply of this amp.

However, you did offer a clue to an alternative explanation:

You just installed a new set of 6550s in the amp. Did the rectifier by any change begin blowing after that? Are the 6550s properly biased? If not, this could pose a problem for the rectifier, *if* the power supply or the power supply design is somehow marginal.

IME the Chinese stuff is cheaper but you pay for it in service headaches.
trelja
3,223 posts
 
Detredwings gives the best advice, "Power supplies can be dangerous and if you don't know what your doing I would suggest you take it to someone who does. I'm only suggesting this because the high voltage stuff can hurt you."

As upset as you are, consider it a blessing that the rectifier and fuse are blowing before something more serious occurs.

If the filter caps do check out OK, look around for a heavy duty short somewhere in the power supply. After that, I'd be suspicious of the power transformer.
devilboy OP
1,176 posts
 
Yes, I'm using slow blow fuses.

The rectifiers and fuses went before AND after I changed output tubes. The second time, electricity arched from one side of the rectifier to the other. Yes, I was told to check the filter caps and look into a short or bad solder joint. Thank you all for your input. I will post my findings ASAP.
trelja
3,223 posts
 
A rectifier arcing over makes it ready for the dustbin. It's heartbreaking, not too mention a pain in the pocket.

Have you already disposed of your 274Bs? If not, and you're willing, I would be more than appreciative if you could send them to me. I decorate my Christmas tree with tubes(seriously), and the 274B would really look great! Of course, I'd be willing to cover all the costs in getting them to me, plus a bit more.
heyraz
177 posts
 
Trelja-
You really decorate your tree with old tubes? I have some old dusty, busted up EL34s from a ST70 that I'm working on. The glass is mostly intact but separated from the bases. They each say Dynaco by Mullard. An authentic set of collectible Christmas Ornaments.
Just wondering-do they just hang or do you light them up too? If so, how are they biased???
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