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Re: non-parafeed transformer preamp?

Well, there are likely to be differences in the sound, but I would not pretend to know which would be better with a 437A. The low plate impedance and high mu of the 437A argue for somewhat different transformers. The low plate impedance allows a low ratio transformer to be used, but the high mu cries for a higher ratio transformer to lose some of the gain. For a single-ended "series" feed (plate loaded with transformer), you could use the LL1660/25mA or LL1660/40mA, depending on how much current you want to run through the tube. You would use connection alternative Q (see datasheet) for a 4.5:1 stepdown. It's a good compromise. For a parallel feed implementation, a constant current source or an LL1668/40mA (or 25mA) in the plate, with the wonderful LL1674 as the output transformer is an alternative.

Kevin Carter
K&K Audio
www.kandkaudio.com

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