How much difference do output transformers do?

[kia2094]

Has any one measured the primary inductance of the stock Epi valve jr. output transformer? I used a signal generator and checked the old VJ I have and got approx 44 Hennery which is way high for such a little transformer. When I checked the stock Crate V5 the same way I got 8 Hennery which makes sense. I have a couple of Edcor transformers on order for the Epi amps I have. When I get them I was going to measure them to see what I get for there primary inductance.
On the low frequency response side the primary inductance is suppose to be in parallel with the reflected impedance and the plate impedance so higher primary impedance equals better low frequency response. The Hi-Fi transformers you can buy are 11 pounds on average with 48 hennery with 5k plate impedance so should be 3db down at 16Hz.(3db down when inductive reactance equals the reflected load in parallel with plate impedance) A guitar output transformer is probably 8 Hennery so if you are 5k reflected impedance you would be 3 db down at approx 100Hz.

On the old Valve Jr transformer I think it maybe that it does not have a gap in its core which it should being a single ended output transformer. That would explain the high inductance for its size but the core will saturate from DC current and distort the output.

Little off the topics here but you raised a good point. But why did you calculated the low frequency inductance base on -3dB? I mean would the design for down -1dB sound better or its no necessary for guitar amps?

Reason for asking is I'm buying a plexi 100w OT , its inductance is base on -3dB (1930 ohm impedence , 82 lower frequency with 3.75 H inductance)

Thank you in advance

[marnold***]

Little off the topics here but you raised a good point. But why did you calculated the low frequency inductance base on -3dB? I mean would the design for down -1dB sound better or its no necessary for guitar amps?

Reason for asking is I'm buying a plexi 100w OT , its inductance is base on -3dB (1930 ohm impedence , 82 lower frequency with 3.75 H inductance)

Thank you in advance

I can't answer your question, but the post was made seven years ago and Jim P hasn't been on here since the end of 2011 so . . . Maybe DVM or someone else might have an answer for you.