[turretslug]

I recall Brush-Clevite as an early name in ceramic filters of the valve era- though the name tends to conjure up images of locomotives rather than precision electronics!

Interfacing modern ceramic filters with all their appeal of high, tailored effectiveness in a small, convenient, inexpensive package to traditional valve IF architecture is something I'd wondered about pretty much since I'd had an interest in vintage radio, but like Bazz, I felt that there wasn't much out there that was really convincing or comprehensive in approach. I'm aware that the filter makers recommend wideband resistive termination on input and output in order to maintain published response characteristics out-of-band, but they often offered matching transformers with their more expensive offerings and Toko et al offered IFTs with low impedance secondaries for typical filters. It's noticeable that the AM sections of modern (i.e. solid state!) tuners frequently have resistive matching between such coupling windings and filter inputs, with the filter output going to transistor base with bias resistors chosen to give appropriate loading. I wonder just what supply voltage 10mm (and smaller) format IFTs would withstand.... At least the 840 series sets run things at quite low HT, even with 230V mains.

I'm slightly shocked that the first circuit in post #7 got through to publication, really- surely that output impedance booboo would have occurred to someone en route? Maybe it was a drafting error and the 2k2 should have been a series resistor, with the emitter resistor separate but accidentally omitted. It's certainly not the first time I've looked at a magazine circuit and thought, "Er, what?"!