[BC] Building radios just for fun

[WFIFeng at aol.com]

In a message dated 10/30/2007 9:30:01 PM Eastern Daylight Time, 
DG19075 at aol.com writes:

> Willie, that little regen is a beauty. Rminds me of the Philmore 7001-CR
>  I built at 15. That was an AC/DC setup using a 12AT6, a35W4 as the
>  rectifier and a 50C5 as the audio amp.
>  

Interesting! Only two gain stages, eh? You must have needed a pretty 
substantial antenna on that puppy! Where did you drop the 20-something extra volts for 
the filaments? (They only add up to 97!) Or did they just run really hot? 
(ouch!)

Even with 4 stages (tho the antenna preamp probably isn't providing a LOT of 
gain) this radio needs a pretty substantial outdoor antenna to pick up more 
than a handful of signals. With just the tiny AM coil (about 1" diameter, 
air-core) it still picks up the 1300 and 1340, but they give me between 80-100mv/m! 
The notch filter makes a huge difference once an antenna is connected!

I just added another triode to the audio section, and that made a big 
difference! (It's a 6111 super-tiny tube, hidden under the chassis, installed after I 
took the photos.) Now with just a few feet of wire, I can hear a fair number 
of stations. Naturally, the performance of this little superregen doesn't even 
come close to a superhet, but it was FUN to build! :)

Another idea I've been toying with has been to use a superhet design, but 
with a high IF, and a fixed low-pass filter on the input. Upconvert the AM band 
to the new IF by mixing with a high freq local osc. The low-pass on the 
front-end will prevent images. Theoretically, I should have no problem tuning the 
entire AM band with only one variable capacitor - the oscillator! All of the 
sensitivity & selectivity will be in the IF strip! I already have one.. a dual 
conversion, 10.7Mhz input to 455Khz. It just needs an osc to run from about 
11-12Mhz with the low-pass front-end with preamp & mixer. Stay tuned! :)

Willie...


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