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The thing is that with tubes the plate currents don't increase a whole lot (with decreasing load), rather they self limit.
I'll try to get around to taking some measurements to demonstrate this.
RG could provide a definitive response, but my guess is that copper losses (as presented in post #13) in a regular guitar OT are negligible, on the simplistic basis that I've never known an OT to self heat appreciably even under heavy overdrive.
The resistances of a transformer winding are maybe 1/50 of the impedance.
Putting 2x the rated load may not cause a problem as such, however it will increase the potential for flyback damage, and will greatly increase the screen grid dissipation, under overdrive conditions. You can check this yourself by measuring the voltage across the screen grid resistor, with the correct load and 2x correct load. You'll see that the screen grids have to dissipate massive power, several times their rated max, and this increases still further with a 2x load mismatch, with a 5 watt screen grid dissipating maybe over 20 watts.
I'm sure that the guy from magnetic components has forgotton more than I've ever known about transformers (I found electro-magnetic theory a real struggle!), but from your quote, in that instance, I feel that he wasn't considering the system as a whole and the other factors that come into play.
The bottom line is that it's very unlikely that either 2x or 0.5x the rated load will cause a problem as such, but if you've got a choice between them, 0.5x the rated load is preferable, as it reduces the potential for flyback insulation damage and screen grid overload.
That's why Fender put a shorting jack socket arrangement on the output, and 2 output sockets wired in parallel.
I'll try to get around to taking some measurements to demonstrate this.
RG could provide a definitive response, but my guess is that copper losses (as presented in post #13) in a regular guitar OT are negligible, on the simplistic basis that I've never known an OT to self heat appreciably even under heavy overdrive.
The resistances of a transformer winding are maybe 1/50 of the impedance.
Putting 2x the rated load may not cause a problem as such, however it will increase the potential for flyback damage, and will greatly increase the screen grid dissipation, under overdrive conditions. You can check this yourself by measuring the voltage across the screen grid resistor, with the correct load and 2x correct load. You'll see that the screen grids have to dissipate massive power, several times their rated max, and this increases still further with a 2x load mismatch, with a 5 watt screen grid dissipating maybe over 20 watts.
I'm sure that the guy from magnetic components has forgotton more than I've ever known about transformers (I found electro-magnetic theory a real struggle!), but from your quote, in that instance, I feel that he wasn't considering the system as a whole and the other factors that come into play.
The bottom line is that it's very unlikely that either 2x or 0.5x the rated load will cause a problem as such, but if you've got a choice between them, 0.5x the rated load is preferable, as it reduces the potential for flyback insulation damage and screen grid overload.
That's why Fender put a shorting jack socket arrangement on the output, and 2 output sockets wired in parallel.
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