Tuner part : What is it ?

That's a Sansui TU-7500

This is a matter of curiousity. Off the secondary of T301 there are two totally unmarked devices circled in red. If they were diodes I guess they would double the frequency but I see no need for that in an AM front end. If the secondary is center tapped and those two parts are identical, then there would be no output from the mixer to the IF.

If they are not identical, I suppose they could be some form of impedance matching. It does seem though on a manufacturing scale like Sansui had back then they could just get the transformer they wanted. Maybe one is a bandpass and the other a bandstop ?

Seems like they would say something about it in case a replacement is needed. It is not indicated at all whether they are under the transformer shield or anything, but such things are indicated in the FM section.

The reason I even saw this is because one is about to come across my bench. But I get curious when things do not make sense.

I understand people wanting to hide their proprietary goodies and all that. In fact I kinda like the way the AGC is set up in this one. But secrecy for an AM tuner ?

Any thoughts ? Like I said it is just curiousity but then again curiousity is what got us all into this mess...

Crystal filter.

I'd guess that they're ceramic filters, probably tuned to or near the IF frequency.

You're right, seeing them connected to opposite ends of T301 and then joined together at the output does seem odd - as you say, if they were identical, the push-pull arrangement would kill the output. Possibly one is tuned above IF and the other below, and they're *intended* to cancel the carrier frequency and let only the sidebands through to the detector diode?

The TU-9900 schematic shows a somewhat more complex arrangement in its AM path - two transformers cross-connected. Each transformer has one of these filters in its "upper arm" connection, and a simple capacitor in the lower arm. Possibly, the TU-7500 arrangement is similar, and the schematic is misleading? There might be just one ceramic filter (e.g. on the upper arm), and a fixed capacitor (on the lower arm) to resonate the transformer?

I think you'll have to look at the board to tell for sure.

I suspect it is to limit the bandpass to 5 kHz or so... thus to reduce common types of interference (10kHz if I recall correctly - it's heck getting old...).

I've seen similar circuits in (crappy) Onkyo analog AM tuner sections.

Mark Z.

That's what I am leaning towards folks, ceramic filters of some type.

The problem is they cannot be exactly the same type. However there are no circuit symbol numbers or anything.

Didn't they make a law that radios had to have AM and FM ? Or certain ones ? Something like that. I think it was back in the 1970s and intended to get FM radios into cars, but the side effect was that high fidelity FM tuners had to include an AM section.

I caught wind of it in a Hifi magazine a long time ago as the author of an article wrote that it wasn't right to make audiophoiles pay for an AM section in their tuner or receiver that they'll never use.

I also noticed that AM only radios in cars seemed to be non-existent after a certain year.

I'm pretty sure I did not imagine that, but there is prctically nothing on the internet about it after a quick search.

The only law of that sort I remember was the FCC requiring televisions to have both VHF and UHF tuners, and they had to tune "with comparable ease". (In other words, a UHF station had to be as easy or as hard to tune in as a VHF station.)

I don't remember any requirement that tuners or radios had to receive both AM and FM. The drift (ar, ar) over the years was towards FM, highly accelerated by the introduction of stereo FM. If either band needed help, it was AM.