395 Poweramp Fuse Blown -tubes- Help!

[Yetti]

Hey Folks,

I Got a 395 Stereo Poweramp paired with the Quad.

Recently it was having problems powering up so i contacted support and they mentioned its probably due to a failed powertube that may have shorted out the Fuse/s.

So i replaced my tubes back last June with Ruby's 6l6GC MSTR's and when i asked the guy, even if i had replaced the tubes that recently it is still possible that it could have failed. he said yes, and explained that any 6l6 Tube wont due the amp it has to be Biased correctly. Ive heard of this before but never thought about it when using the tube, i figured they would be ok with a mesa amp.

So the guy instructed that replace the fuse/s and turn the amp on and watch for one of the tubes to flash or something and then the fuse will most likelyy pop again...that will diagnose the failed tube. Is this correct? So my main question is which fuse do i replace? there are 3 on the 395 one for channel A One for channel B and then one labeled Mains Im gona assume this is the one that i need to replace. Is that correct? Or should i just replace them all? Also where can i locate a fuse? hardware store, Electronics store?

Then back to maybe a bigger concern the tubes...the guy at service said the bias on mesa amps are something like 6-8 or something. So i dont know how that would translate or how to figure out that from the tubes i have in there now. maybe you all can help me with that too. I wrote down every bit of info i could find on the box/tube when i replaced them just incase that info was important (Duh i guess it is).

Heres just one of the 8:
6l6GC MSTR RUBY

Plate Current (MA): 21.1 (This the Bias?)
28
Transconductance: 2650
Matchup #19 - PC44 TC 3000

So Recap:
Do i Replace all Fuses?
Where to find them?
Are my current Ruby Tubes Fuxing my Powersection? / Overloading it?
Replace them tubes?

Help would be freaking awesome guys.

Cheers
-Rob

 

[marshman]

I'll take a shot...

First off, yes, replace all the fuses. They're cheap enough, no sense askin' for trouble. If you're lucky, you may find that one side is consistenly reacting badly and you can narrow the search for the problem. If you can determine which side is acting up, you can start hopping tubes from one side to the other until you determine which tube(s) is acting up and replace the offensive unit.

Fuses are available at both electronics stores and hardware stores, though around here, I typically can't get all my fuses at one place...eg, the hardware store won't have all the values I need, so I may have to go get a few at Radio Shack.

The number written on the tubes and/or packaging is test data determined by whomever tested your tubes and applicable pretty much only to those tubes on that tester. As long as all the numbers are about the same for all the tubes, that's cool. You might get tubes randomly from another supplier with similar numbers, but I wouldn't count on it.

I hate assume the worst, but let's go to basics--even while you're troubleshooting, never fire a tube amp up WITHOUT a speaker plugged in--which means 2 cabs if it's a stereo power amp like my 400. And of course, there is more than enough voltage inside that amp to kill you, so don't go pokin around INSIDE the chassis if you don't know what you're doin'. Changing tubes and fuses is safe, as long as everything is OFF.

Good luck.