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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 13th Sep 2017, 12:33 pm   #1
John M0GLN
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Default RCA 45X11 valve description.

One of my sets is a RCA Victor 45X11, I have just changed a few caps' and it's working well, but there is one thing that puzzles me with regard to the valve descriptions on the schematic, the 12SA7 which is a heptode mixer-oscillator is shown as a '1st DET-OSC' and the 12SQ7 which will be doing the detecting is shown as the '2nd DET-AF-AVC'. what does DET stand for with regards to the 12SA7? I've looked on the web but other than finding out that it's a common description in US radios I've seen nothing else, I expect it will be something simple and obvious to all but me.

Thanks

John
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Old 13th Sep 2017, 12:40 pm   #2
paulsherwin
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Default Re: RCA 45X11 valve description.

American terminology for a mixer-oscillator?
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Old 13th Sep 2017, 12:44 pm   #3
G6Tanuki
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Default Re: RCA 45X11 valve description.

Frequency-changers were often described as "1st Detector", not just by the Yanks. I recall this term being used in the 1930s Admiralty wireless-telegraphy handbook too.
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Old 13th Sep 2017, 1:43 pm   #4
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Default Re: RCA 45X11 valve description.

From a 1933 Practical Wireless advert.
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Old 13th Sep 2017, 1:51 pm   #5
Boater Sam
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Default Re: RCA 45X11 valve description.

Just old terminology - detector - It is probably a hang over from TRF sets to differentiate from an RF amplifier or audio amplifier as the first valve would then be the detector.
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Old 13th Sep 2017, 4:39 pm   #6
usradcoll1
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Default Re: RCA 45X11 valve description.

Quote:
Originally Posted by paulsherwin View Post
American terminology for a mixer-oscillator?
That type of valve is also known as a "Pentagrid Converter".
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Old 13th Sep 2017, 8:01 pm   #7
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Default Re: RCA 45X11 valve description.

It's an interesting historical hangover that has a certain charm- as said, probably from the earliest TRF days. I think there was a tendency to increment the complexity of a home-made set in the early days as savings and confidence increased, possibly the original TRF detector diode/non-linearly biased triode etc. would then get used as a mixer in some embryonic superhets, thus becoming "1st detector" and the term stuck? Perhaps "detector" could be elaborated as "vital non-linearity stage making the signal usable by the next stage", whether that next stage be high-impedance headphones, AF or IF amp. Latterly coming under the cover-all generic "modulator"- even if it demodulates!
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Old 14th Sep 2017, 8:25 am   #8
John M0GLN
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Default Re: RCA 45X11 valve description.

So 'detector' in this context is a term from the early days of both British as well as American radios and doesn't necessarily mean it's a demodulator like I thought it would.

Thank you all for your interesting replies.

John
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Old 14th Sep 2017, 8:40 am   #9
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Default Re: RCA 45X11 valve description.

I had been puzzled by those terms too.

http://www.vintage-radio.net/forum/s...d.php?t=114728
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Old 14th Sep 2017, 9:28 am   #10
Nuvistor
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Default Re: RCA 45X11 valve description.

A good read from this web site.

http://antiqueradios.com/superhet/


Quote. Paragraph from the page.

Heterodyne detection provided an apparent amplification of the received signal, an important effect since at first no other method of radio-frequency amplification was known (the Audion was used only as a detector for several years after its 1906 invention, not as an audio- or radio-freqency amplifier).
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