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Circa '46 Emerson portable tube radio
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
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http://www.youtube.com/user/radiotvphononut |
#2
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Intriguing design that set has.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#3
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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. |
#4
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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.
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Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten. |
#5
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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.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
#6
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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. |
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Hope to see you at the next meet! |
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I'm not that fast my self (though I'm exponentially better than when I joined ARF, having prior to then written 99.99% of all words I'd wrote in pencil)...There have been a number of times folks have slipped similar ideas to mine in before I had them typed....Trust me, you will feel dumber if you open a thread in a new tab so that you remember to write a reply next time you have a chance, and then don't refresh before submitting it 10,30,90 minutes later, only to find your the third person in line to say the same thing....I've done that. Wow, it's been a few years since the last time I was called kid...I was beginning to forget what it is like, and stopped thinking of my self as one a good while ago... I guess I'm still immature enough to fit the definition.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#9
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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.
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http://www.youtube.com/user/radiotvphononut |
#10
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Audiokarma |
#11
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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.
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#12
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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.
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#13
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Some makes of TV sets, still used 21MHZ IF's, till the mid 50's. Admiral was unique in that respect, the VHF only models, were 21MHZ, where the UHF/VHF models were 41MHZ. IIRC, they did that till the late 50's, or so. |
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