Mesa Dual rectifier replacing 6L6 blows a resistor, anyone ?

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andre tchmil

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Jun 4, 2004
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One of the four 6L6 tubes in my Dual rectifier started to ring ,When I replaced the tube with a Fender branded one , I blew a resistor (R233, or R223).
Original 6L6 was Mesa labeled?

Any idea ?
 
To answer this question one would need to have the tube curves.

Grid bias vs plate current. Are the mesa china tube and the fender russian? Do the curves match?

The one tube you used could draw way more current than the other tubes at the same bias that the other tubes are set at.
 
I wouldn't recommend mis-matching tube brands.... Also, most Mesa amplifiers are fixed bias and do not have adjusters.

You could probably run it on 2 power valves rather than 4. I'm not familiar with your particular Mesa, but it is simple with Marshalls - you need to set the bias for half, and also change the load to compensate. Good if you don't often get it up to full volume!
 
short story

I had a ampeg tube amp at the house that had 6l6s. They looked like china tubes so I changed them to russian tubes and the tubes red plated before I could adjust the bias voltage
They red plated fast like a bad output coupling cap.
The russian tubes needed more - grid voltage than the china tubes I don't know if it was bad tubes or just very different curves.


I have not seen the curves for the russian or china 6l6s but I would guess they are different. I know one can find NOS curves but I would not trust them except for NOS.
 
Are those Fender tubes new????
And were they OK??
Look to Groove Tube the same type of tube and WATCH the number behinde!!!!!!! Look up what number you need for that Mesa B.
How many hours did they run already??
Every 400..500 hours new tubes is the best , just renember that!!
 
Mesa tubes I've seen have been Chinese. Must rebias if switching to Russian 5881 types. Fender used 5881 Sovteks relabled as Fender 6L6GCs for a while. Not sure about now. Don't mix brands/types.

It's not hard to put in a bias pot to adjust for any tube type.

Schematic can be found here.
http://www.freeinfosociety.com/electronics/schemview.php?id=507
 

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