EL84 Parallel SE transformer

[Helmholtz]

I don't know if you can drive a pair el84s at 4.3k with 350v plate.

Optimum plate impedance for a pair of EL84s in PP is around 8k.
4.3k would result in excessive plate dissipation with signal.

[dunit]

True, but there are drawbacks.
The primary winding of an OT is optimized for some nominal impedance.
Using it with lower impedance increases the primary current and thus the DCR losses.
DCR losses increase with the current squared, so the power loss can be significant.

Using the OT with higher than nominal impedance sacrifices bass response.

I understand that it's not about Hammond doing something different with their OT's, that it's a matter of ratios that work with any OT.
And I agree with Helmholtz's caution. So maybe it's that Hammond gives the options for that particular model because they build it
to withstand the rigors of "mis"-matching as they suggest. Just a thought since they don't mention it with other OT's they make and sell.