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previous: JR Liam , I think it goes othe... -- 3/20/1998 11:30 AM

Re: impedance selection

3/21/1998 12:44 AM
GVB	Re: impedance selection Yep, that's right. I've seen countless posts that give the wrong information. Many people assume that tube amps and solid state amps respond the same to a speaker load. This is not the case. Most solid state amps have the load attached directly to the transistors/mosfets. A lower impedance load will draw more current and destroy the output devices. You can run most solid state amps without a load till the cows come home and not have any problems, but I wouldn't necessarily recommend this procedure to anyone. Most tube amps on the other hand, have the tubes coupled to the load through a transformer. Going to a lower impedance load causes an impedance mismatch and therefore the power output will go down. The tubes themselves will run a little hotter, and will not last as long as when run properly, but it probably won't be enough to do any damage. Using a higher than rated load will also cause a reduction in power output. The problem with this is that speakers exhibit back EMF and can induce flyback in the primary of the output transformer. The voltage shoots up incredibly high and arcing occurs across the tube sockets. If you're lucky, all that will happen is fried sockets. At worst this can damage the tubes themselves and/or puncture that insulation of the output transformer primary windings. In other words, do the exact opposite of solid state amps, and you should be OK, but you will ware out tubes faster. GVB

3/21/1998 12:44 AM

GVB

Re: impedance selection

Yep, that's right. I've seen countless posts that give the wrong information. Many people assume that tube amps and solid state amps respond the same to a speaker load. This is not the case. Most solid state amps have the load attached directly to the transistors/mosfets. A lower impedance load will draw more current and destroy the output devices. You can run most solid state amps without a load till the cows come home and not have any problems, but I wouldn't necessarily recommend this procedure to anyone.

Most tube amps on the other hand, have the tubes coupled to the load through a transformer. Going to a lower impedance load causes an impedance mismatch and therefore the power output will go down. The tubes themselves will run a little hotter, and will not last as long as when run properly, but it probably won't be enough to do any damage. Using a higher than rated load will also cause a reduction in power output. The problem with this is that speakers exhibit back EMF and can induce flyback in the primary of the output transformer. The voltage shoots up incredibly high and arcing occurs across the tube sockets. If you're lucky, all that will happen is fried sockets. At worst this can damage the tubes themselves and/or puncture that insulation of the output transformer primary windings.

In other words, do the exact opposite of solid state amps, and you should be OK, but you will ware out tubes faster.

GVB

Replies:

liam Yes, but running 16 ohms on an 8 oh... -- 3/21/1998 6:26 AM