Oarta output transformer

It looks like the Lundahl LL1623 rated at 90mA would be the best choice for this amp. The amorphous core price is less than half of the Tamura, but more importantly, it is available. The interstage transformer would be the next choice. This would probably be the most important choice, given the different voltage swings that needs to be accommodated by the different tubes.

I think at this point, it would be important to at least try to limit the range of tubes to be used. This has to be correlated with my current stash of tubes. In this, I would say that there are four families that I would like to run:

1. 45, 145, 245 and 345. I have a number of pairs and have been universally hailed as an excellent audio tube.
2. F2a. I have three pairs of these long life tubes.
3. KT88/EL34 family. I have two quartets of the KT88 and EL 34.
4. 300B. I have one pair. 

Looking at the above, it would make most sense that I provide more effort towards the first three families given the volume of tubes on hand. With the 300B narrowed out, the voltage swings required are now limited to 30 Vpp to 60 Vpp, a little more sensible. This would mean that a tube with a gain of 20 would be plenty. At this point the 5687 and C3g seems the right direction. If I use a higher gain tube, I can use a step down interstage, which should be a good think overall. The other option, is to allow a different tap on the interstage to be used to connect to the grid of the output tube, which can select between say 1:1 and 2:1. But this may affect the performance and bandwidth of the interstage.

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