Any problem running Hammond 1650T at 3.8K?

[priesty]

I've read a bit on this forum and others about potentially using the 1.9K Hammond 1650T output transformer as a OT for a KT88/6550 pair.

I know connecting the 4ohm secondary tap to a 8ohm load should (in theory) give an output primary impedance of 3.8K, but is this at the expense of Bass responce? Some people out there seem to think so, but I can't see why this would be the case.

[redelephant]

Well, if the OPT has an inductance that gives a cutoff at 20Hz when it acts as a 1900ohm impedance, the same inductance will then give a cutoff at 40Hz when it loads into 3800ohms.

In other words the inductance of the tranny acts with the load impedance to form a high pass filter, if same inductance is loaded with twice the impedance, the cutoff frequency is doubled, and vice versa.

For guitar this is only a good thing, so no worries.

The inductance you need for a given cutoff into a given load: Z(L)=2pi*f*L, giving L=Z(L)/(2pi*f) which means for 20Hz and 1900ohms the L is 1900/(2pi*20)=15Henry. And if we have twice the impedance the inductance needs to be twice as much for same cutoff: L > = 3800/(2pi*20) = 30H.