[kingdeezie]

Hello everyone. I've come to the knowledgable folks here for their opinions on the matter.

I have a pair of Manley Neo Classic 250s that I bought used in December '10. Initially when I got them, I would assume because of the jostling of the east coast sojourn, one of the tubes blew bad. It took out a cathode resistor and the fuse. I replaced both of these things and got the amplifier working again.

A couple of weeks after that, I decided that I was going to completely replace the power output tubes. I purchased a set of 20 from boiaudio works for a decent price.

The tubes are new production EH EL34s.

Out of that batch of 20, two have went; that's 10 percent failure rate on these tubes.

It hasn't been the same monoblock or the same position in the two instances. One tube blew in the first 50 hours.

The newest fatality I found today when checking biasing. The tube wouldn't bias below .700, when Manley calls for .275-.285.

I turned the amplifier off, and removed the tube, replacing it out of some spares I have for backup.

Is this par for the course with these new production tubes, or do I have a problem?

All of the other tubes are ok, and the biases only slipped a little bit with minor readjusting needed.

This is my first tube amplifier so each of these little facets of what may be reality are new to me.

What say you?

[Berndt]

Send them back to manley for a tune up.

[ltr317]

It's probably the poor quality control of the EH EL34s.  I had the same problem with new EH EL34s.  I bought a quad and one blew out after a couple of weeks, then a second tube in another position went a few days later.  I bought two replacements, and one went bad after a few days.  That's a 50% failure rate on new tubes with EH.  I spoke with two friends who also used the same EH type, and they said the same thing happened with their output tubes.  None of us are using EH EL34s any more.  I'm currently using Svetlana Wing Cs, but have used other companies and none gave me any problems.   

[rollo]

  Dosn't appear to be the amp, just tube failure. Hopefully you bought them with a 30 day warantee. It also pays to have them tested and matched. This is not unusual it does happen now and then. For new tubes Parts Express has always come through for me. Grant Fidelity as well.
   



charles

[kingdeezie]

Well its good to know that its most likely just the tubes; although it makes getting decent tubes a pain in the ass. 

Manley voiced these with EH; so I would get a little weary of messing with the sound with another brand of tube.