dodger916
Well-known member
- Joined
- Aug 29, 2007
- Messages
- 2,403
- Reaction score
- 4
Mesa manuals specify one-step increases are safe mismatches, for instance an 8 ohm load in the 4 ohm tap, or a 16 ohm load in an 8 ohm tap. But 16 ohm load in a 4 ohm tap...I dunno.
HOWEVER, some say a step up in resistance is bad as it can hurt the transformer (contrary to what Mesa says), while a step-down may exhaust the power tubes faster but is safer for the transformer. I'll see if I can find the links and update this post.
Here's the long answer:
http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#mismatch
Here's an excerpt from it:
"however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all. "
This is a great paper! Go to the top and see all the topics. It was written by R.G. Keen, who I've heard is a reknowned tube amp guy.
HOWEVER, some say a step up in resistance is bad as it can hurt the transformer (contrary to what Mesa says), while a step-down may exhaust the power tubes faster but is safer for the transformer. I'll see if I can find the links and update this post.
Here's the long answer:
http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#mismatch
Here's an excerpt from it:
"however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all. "
This is a great paper! Go to the top and see all the topics. It was written by R.G. Keen, who I've heard is a reknowned tube amp guy.
