Posted by Damir [ 213.202.115.85 ] on February 15, 2006 at 16:11:43:
In Reply to: heads n cabs posted by Ben on February 15, 2006 at 06:31:40:
100W amp probably has 4 output tubes (most often EL34 or 6L6GC) in push-pull parallel. Simplified, first and second power tubes are "push" half, wired in parallel. Other two tubes (3rd and 4th) are "pull" half, and also wired in parallel.
You can remove, say first and fourth (or 2nd and 3rd), and have a PP amp with only two output tubes. Power would be halved, and most of "half-power" switches on some amps work that way - to disconnect (cathodes) two of four power tubes.
Then you have the "proper load" part - theoretically, you must now connect your (say 8 Ohms) cabinet to the 4 Ohms tap, to have the "proper" load for the power tubes. Some authors find it unecessary (see "London Power" FAQ), but better be carefull with "Marshalls".
I`d simply buy 100W+ guitar speaker and replaced 50W model in the box... 
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