On Mon, 28 Feb 2011 11:41:15 -0800, Joel Koltner wrote:

Hi Tim,

"Tim Wescott" wrote in message
...
Are you talking transistor IF transformers, with one slug each, or
tube- type, with two?

One slug each. I hadn't remembered two two-slug types, but now that I
think about it, I think I have seen them.

Old radio texts. If you still get up to Portland from time to time,
dig through Powell's Technical books.

Good idea, will do.

What are you trying to do? There's good reason for not wanting to have
a circuit with a bazillion tweaks that all have to be right for the
thing to be in tune.

Yeah, although it's kinda a sad commentary that many an "FM receiver"
today doesn't have a tuned front end and, as such, actually performs
rather wose than radios from 30 years ago now, you know?

As for what I'm trying to do... mostly just fully understand how the
cheap little transistor radios they made up until a decade or so ago
operated; I sure couldn't have designed one at the point I graduated
from college, and these days I finally feel as though I'd have a decent
shot at it. (On the other hand, I did feel I could have designed a 6502
when I graduated from college, and then some fancier superscalar
processor by the time I finished grad school -- so it's not like I
didn't get anything out of it.)

(On the other hand, I *have* designed various radio transmitters and
receivers that work well, they were just done more at the
MMIC/IC/MiniCircuits-parts level rather than the "discrete
transistor/coupled coil" level -- you know, the kind of designs industry
will actually *pay* you to do. :-) You probably don't do many PID loops
with op-amps anymore I expect?)

Does Mouser still sell them?

The point of the IF transformer was twofold: to provide selectivity, and
to give a good impedance match between stages. I think there must have
been a standard receiver design, as there just seemed to be one choice
for each coil -- this in spite of the fact that as soon as you start
juggling feedback and/or standing currents, you change the impedances,
and therefor the required transformer.

I think if I were going to design a broadcast-band receiver, I wouldn't
just re-do the old schematic from 1960 -- I'd start from a clean sheet of
paper, and see where I could go from there. (Actually, I think the first
thing that'd go onto that clean sheet of paper would be an ADC -- I'm a
luddite in a lot of ways, but not in how I'd like to see a receiver laid
out).

--
http://www.wescottdesign.com