Circa '46 Emerson portable tube radio

[radiotvnut]

Here's an interesting Emerson portable radio that I recently picked up. It must be one of the better models, since it has a 3-gang tuning capacitor and RF stage, as well as dual audio output tubes. A 50B5 output tube is used when the set is operated off of AC power, probably for greater volume and better tonal quality. When operated on batteries, a 3Q5 output tube is switched in circuit. Here is the schematic: http://www.nostalgiaair.org/PagesByM...8/M0004628.pdf

[Electronic M]

Intriguing design that set has.

[dieseljeep]

Originally Posted by Electronic M

Intriguing design that set has.

I have three models like that. Two have the 50B5, 35W4 combination and one has the 117N7, rectifier, output combination.
If you notice, it uses a filter choke in the power supply. It must be, because of the heavier current demand of the tube filament circuit. Also note, the IF frequency is 262 KC. The audio output transformer is also dual primary, to match the plate load impedance of the two different output tubes.
BTW, I never saw the model using the octal output and rectifier tubes. It must've been a real short production run.

[Jeffhs]

Someone must have goofed on that IF frequency. Shouldn't it be 455 kHz? Also, if this radio has push-pull audio output, shouldn't the tubes be identical, e. g. two 50C5s?

BTW, one of the knobs is mismatched; I don't know which one is still original. Someone must have lost one or the other and replaced it with one from the junk box.

[Electronic M]

Originally Posted by Jeffhs

Someone must have goofed on that IF frequency. Shouldn't it be 455 kHz? Also, if this radio has push-pull audio output, shouldn't the tubes be identical, e. g. two 50C5s?

BTW, one of the knobs is mismatched; I don't know which one is still original. Someone must have lost one or the other and replaced it with one from the junk box.

Your waaay off base.... It is not a push-pull output, but rather it uses a single ended output with the 3Q5 only working in battery power mode, and the 50B5 only working when the radio is ran off AC line voltage.

262kHz is the second most common IF frequency (455 being first by a VERY wide margin), and IIRC was common in tube era car radios.

[dieseljeep]

Originally Posted by Electronic M

Your waaay off base.... It is not a push-pull output, but rather it uses a single ended output with the 3Q5 only working in battery power mode, and the 50B5 only working when the radio is ran off AC line voltage.

262kHz is the second most common IF frequency (455 being first by a VERY wide margin), and IIRC was common in tube era car radios.

Hey kid! I didn't think, I took that long to enter my opinion on the thread. We are both, very right in our findings. I never was very fast in my keyboarding.
Hope to see you at the next meet!

[dieseljeep]

Originally Posted by Jeffhs

Someone must have goofed on that IF frequency. Shouldn't it be 455 kHz? Also, if this radio has push-pull audio output, shouldn't the tubes be identical, e. g. two 50C5s?

BTW, one of the knobs is mismatched; I don't know which one is still original. Someone must have lost one or the other and replaced it with one from the junk box.

There's nothing in the rules, that say the IF frequency, has to be 455KC. I'm actually surprised that the IF is 262KC. I guess they used it to minimize images, the same way, they used 262KC in most car radios.
I still maintain, that the radio is highly engineered, to provide performance that exceeds the competitive makes.
Regarding the output stage, it is not push-pull, but designed to run on AC, as well as battery power, so that's the reason for the novel audio output stage. Zenith could have used that idea on their TO's, instead of the push-pull 1LB4's, that didn't sound, nearly as good.
One of the knobs, looks like a GE. The original knob, was either lost on broken.

[wa2ise]

Originally Posted by dieseljeep

There's nothing in the rules, that say the IF frequency, has to be 455KC. I'm actually surprised that the IF is 262KC. I guess they used it to minimize images, the same way, they used 262KC in most car radios.
...

TV sets back in the early post war days used an IF around 22MHz, then later 45MHz. But that was after channel 1 was deleted (channel 1 would have been in the middle of the 45MHz IF bandwidth).

Some prewar 45MHz band FM radios used an IF around 8MHz.

I think the FCC avoids assigning powerful transmitters on the popular IF frequencies. 455KHz, 10.7MHz, 45MHz and so on.

[dieseljeep]

Originally Posted by Electronic M

Intriguing design that set has.

BTW, be aware, that the set is a hot chassis design and there's a lot of area, to get a shock on. When you finish the repairs and restoration, make sure the back is on, when demonstrating or just using it.

[radiotvnut]

Fortunately, someone on one of the facebook antique radio pages is sending me a knob. When I get caught up with other projects, I'll tear into this one. Concerning IF frequencies, I've found that a lot of superhet radios made before the mid '30's to be all over the map, in terms of the IF frequency. That's why I always look at the service information, especially on older sets, before assuming that the IF frequency is 455 KC.

[dieseljeep]

Originally Posted by radiotvnut

Fortunately, someone on one of the facebook antique radio pages is sending me a knob. When I get caught up with other projects, I'll tear into this one. Concerning IF frequencies, I've found that a lot of superhet radios made before the mid '30's to be all over the map, in terms of the IF frequency. That's why I always look at the service information, especially on older sets, before assuming that the IF frequency is 455 KC.

Regarding odd IF frequencies, look at the various comm sets built for the Armed Forces. The single band command sets, every model has a different IF frequency. The BC348 is 915KC IF. IIRC, all of them, including the last production run, built by Wells Gardner.