calculating plate to plate impedance?

[the_bleeding]

So i have a transformer with a published primary through impedance, and secondary impedances, and it would be really sweet if anybody would share how i can calculate the plate to plate load. I've looked and looked everhwere, and havent been able to find any clear instruciton on how to really do the math behind designing a class A/B output stage.

Currently im running 2xkt88's at 480v on the plates, in tetrode configuration, with 1900ohm primary, which has presented me with problems.

My goal is to run 2x6550's at 480v B+, in ultralinear configuration, and i'm trying to figure out whether i want a 5000ohm primary, or 6600ohm primary, and what the mathematical differences between those transformers would be - or even just the optimal impedance so i can select a transformer elsewhere.

[flemingmras]

So i have a transformer with a published primary through impedance, and secondary impedances, and it would be really sweet if anybody would share how i can calculate the plate to plate load. I've looked and looked everhwere, and havent been able to find any clear instruciton on how to really do the math behind designing a class A/B output stage.

Currently im running 2xkt88's at 480v on the plates, in tetrode configuration, with 1900ohm primary, which has presented me with problems.

My goal is to run 2x6550's at 480v B+, in ultralinear configuration, and i'm trying to figure out whether i want a 5000ohm primary, or 6600ohm primary, and what the mathematical differences between those transformers would be - or even just the optimal impedance so i can select a transformer elsewhere.

According to the General Electric datasheet, a 6550A with a 450 volt plate voltage in ultra linear configuration calls for 4K ohm plate to plate load, so the 5K ohm primary would probably be your best bet.