The Hook-Up Data for Hammond's 125 series [Single-Ended] Output Transformers provides a list of values for Speaker Impedance at multiple Taps, which allows Primary Impedance matching with a circuit's Output Tube(s).
http://www.hammondmfg.com/pdf/5C_125SE.pdf (http://www.hammondmfg.com/pdf/5C_125SE.pdf)
QUESTION: If substituting Hammond's 1750A Reverb Transformer as the OT in a low-powered [Single-Ended] design, can I safely connect a 4 Ohm speaker (instead of 8 Ohm) to drop the Primary Impedance to roughly 11k (instead of 22k)?
http://www.mouser.com/ds/2/177/EDB1750A-69544.pdf (http://www.mouser.com/ds/2/177/EDB1750A-69544.pdf)
Thanks,
-Corey
as far as i remember this action will change primary impedance to 22k / sqrt(2) not to 22k / 2
Impedances mirror directly.
A possible issue with using a "22K" at 11K (especially in SE use) is that the Maximum Current is largely unchanged. To stay strictly "inside the lines" you should run the same current at half the supply voltage, and expect half the power output.
In this case: I'm pretty sure the Fender Reverb transformer design comes from a much larger, say 1 Watt, radio output, and that Fender under-runs it putting 0.1W into a tank.
> 22k / sqrt(2)
You are thinking of Turns Ratio. And you have it backward: square of turns-ratio. If Corey were to re-wind with half as many primary turns, it would become 5.5K:8.