Stromberg-Carlson AM-FM tuner

[Conelrad]

I won this jewel on a Texas auction. I just love vintage all-tube tuners like this, especially those with wideband AM hi-fi mode.

More to come when it arrives!

SC tuner.jpeg (97.94 KiB) Viewed 271 times

Dennis

[William]

Nice looking, Dennis, what will you pair it with?

Bill

[Hi-Fi-Mogul]

Can you explain what wideband AM hi-fi mode is ?

I see some nomenclature on the band
selection dial that indicates that.

Thanks.

[TC Chris]

The bandwidth determines things like selectivity and audio frequency response. Wideband = less selective but better fidelity; narrow band = more selective (easier to separate stations) but more limited response.

I think the FCC still limits AM transmissions to a fairly narrow-band signal, but in the old days, some big urban stations could transmit high fidelity audio, and a tuner with the wideband response could take advantage of it.

It would be interesting to know if there are stations that do it now. I recall reading somewhere that as AM stations died off, some were not bothered by adjacent channels and were transmitting better quality audio.

Chris Campbell

[Conelrad]

Once it arrives, I'll get busy doing the usual preventative maintenance on it: Tube checks, electrolytics change-outs, resistor value tests.

I'll have to find a Sams or original schematic to help out. After all, is it over 70 years old now. (Me too).

This is my 3rd tuner like this. The others are a 60's Heathkit Hi-Fi AM only, and a monster Altec-Lansing with dual eye tubes, and the rest all octals. A tall order on the FM side for 100 MHz signals!

As far the hi-fi aspect goes, AM tuners of that sort are usually of two types: TRF, and swamped-IF wide bandwidth superhets, usually out to 30kHz wide to allow 15kHz audio. Certain late 30's high-end radios from builders like Scott, Silver-Marshall, and Hammarlund had variable IF strips for good listening.

The JW Miller company marketed a crystal set with two-stages of LC networks for wideband AM, no power needed. It sounds amazing.

A lot of vintage broadcast transmitters could easily pass high quality audio, and the newer PWM high-efficiency transmitters (over 82% from AC line in to RF out). An interesting article: https://sound-au.com/articles/am-radio.htm

It is just the usual crappy sound from most superhets that sour people from listening.

I also have a first model solid-state GE Superadio, with wide & narrow AM performance. It s fun to have friends hear the difference on it.

If one is lucky not to live in a crowded AM signals area, it can be amazing just how good AM can sound. I live some 80 miles from a 50kW powerhouse that plays mixed rock with live DJ's and few commercials. What's not to like?

Dennis

[William]

When you get a minute, Dennis, how about sharing a photo of the Heathkit and the Altec-Lansing, I would love to see photos of what those look like especially the Altec-Lansing.

Bill

[electra225]

Dennis, I'm assuming you are talking about 830 "The Drive" out of Tucson? The amazing thing about that station for me is that even a weak radio that has trouble with some of the more local stations (such as 1440) will pick up 830 The Drive. I'm not normally enthusiastic about old rock music, but they have such a mix that I find myself spending more time on that station.

[Conelrad]

There are five 50kW AMs in AZ, two in Tucson: KDRI 830, and KUAZ on 1550, KFNX Phoenix on 1100, KPXQ Phoenix 1360, and KTNN Window Rock 660.

Daytime listening is easy in most areas of the state.

Here is a link to all of them in the US for the rest of you: https://en.wikipedia.org/wiki/List_of_5 ... ted_States

Dial around and see what you can hear.

D

[Conelrad]

I can't count...6 50's in AZ.

D

[electra225]

I listen to KFNX occasionally. Wasn't the original KOY at 550 AM a 50K watter in its day? I loved that station and I listened to it all the time. They played oldies, back to the big band era....

[Conelrad]

Nah, the max KOY @ 550 is 5kW. They got started back in the 1920's as a ham station, and it got a commercial license eventually.

[electra225]

KOY was one of the Phoenix stations that came in so strong, it would overlap the image in an eye tube on an old radio. I also liked KOOL-AM. I don't remember the frequency, but it was in the 700-900 range somewhere. KMYL was on for a year or so at 1260 AM and featured Wink Martindale with the Music of Your Life programming. Probably the best mix of music I ever heard on radio. I don't know what happened to it. One day it was just gone.....KNIX used to similcast at 1580 when Buck Owens still owned the station. I got fired one day because of that station. Therein lies a tale......

[Conelrad]

The best propagation in the AM band is from 700 down to 550 kHz. It can 5kW sound like 25.

[electra225]

I would listen to KOY on a TRF radio that I still have, as you know. That radio sounded like FM on KOY. There is no local oscillator, so there is no birdies or whistle and the fidelity seems better. TRF radios are stronger at the top of the dial than the lower end, but that radio didn't know that. It's only issue is with stations running together. No local oscillator to keep them honest. I used a ceiling fan for an antenna, and that seemed to be quite sufficient....

[Conelrad]

It has arrived in fine shape. Poor thing is rife with leaky bumblebee caps, a bunch of hours work due there. Most of the tubes are original S/C branded, wow after 72 years. A fitting birthday arrival, as I tuned that age today.

A short synopsis is the AM section has a tuned 1st RF amp, to a upconverter/mixer, then ran thru the FM section IF @ 10.7mHz with the according increased bandwidth. Clever design.

More to come as I get time to get pix & beat it back into a living, playing example.

D

[William]

Happy Birthday, Dennis, and that does make a perfect birthday present to yourself. Have fun with it and I can't wait to see more photos and your story of bringing it back to life.

Bill

[TC Chris]

Whoa.... the aM IF is 10.5 mHz? Wow, that's an interesting was to run AM and FM through the same tuner!

Chris Campbell