RCA 45X11 valve description.
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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 |
Re: RCA 45X11 valve description.
American terminology for a mixer-oscillator?
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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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Re: RCA 45X11 valve description.
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From a 1933 Practical Wireless advert.
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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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Re: RCA 45X11 valve description.
Quote:
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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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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 |
Re: RCA 45X11 valve description.
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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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