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-   -   RCA 45X11 valve description. (https://www.vintage-radio.net/forum/showthread.php?t=139786)

John M0GLN 13th Sep 2017 1:33 pm

RCA 45X11 valve description.
 
1 Attachment(s)
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

paulsherwin 13th Sep 2017 1:40 pm

Re: RCA 45X11 valve description.
 
American terminology for a mixer-oscillator?

G6Tanuki 13th Sep 2017 1:44 pm

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.

Nuvistor 13th Sep 2017 2:43 pm

Re: RCA 45X11 valve description.
 
1 Attachment(s)
From a 1933 Practical Wireless advert.

Boater Sam 13th Sep 2017 2:51 pm

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.

usradcoll1 13th Sep 2017 5:39 pm

Re: RCA 45X11 valve description.
 
Quote:

Originally Posted by paulsherwin (Post 975405)
American terminology for a mixer-oscillator?

That type of valve is also known as a "Pentagrid Converter".

turretslug 13th Sep 2017 9:01 pm

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!

John M0GLN 14th Sep 2017 9:25 am

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

ukcol 14th Sep 2017 9:40 am

Re: RCA 45X11 valve description.
 
I had been puzzled by those terms too.

http://www.vintage-radio.net/forum/s...d.php?t=114728

Nuvistor 14th Sep 2017 10:28 am

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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