Einstein's Knack (for Refrigeration)

https://www.wired.com/story/einsteins-little-known-passion-project-a-refrigerator?google_editors_picks=true

Intuitive Repair of a Sony Shortwave Portable

A few years ago my wife got me this nice little Sony ICF-SW7600GR receiver.   On the front it proclaims that it is "AM DUAL CONVERSION" and "PLL SYNTHESIZED."   It has a BFO, and a filter of suitable width for SSB.  It also has a synchronous detector -- it generates an internal carrier that matches the frequency and phase of the carrier being transmitted by the SW broadcast (or ham AM) transmitter.  This helps overcome the selective fading that often plagues AM signals.  Sony advises switching to USB or LSB once the synchronous generator locks onto the carrier.  Pretty cool. 

The BFO is the reason I wanted this receiver. And wouldn't you know, when I dropped it,  it landed EXACTLY on the little BFO fine tune control pot.  It was as if the Radio Gods disliked all the fancy digi PLL synchronous IC circuitry.   

I tried without success to find the value of the destroyed pot.  Finally, last week I just decided to have a look in there to see if I could just figure it out. 

On the board I could see that the pot only connected at two places, so I figured it would be a varactor circuit on the BFO with one end of the pot to DC and the wiper to the varactor diode.  I figured I'd try a 10K pot. 

This seems to have been some good radio intuition.  It works.  I went with a small trimmer because it is less obtrusive and because once I set the BFO in the right spot, I think the de facto channelization of the 40 meter ham band will keep most of the SSB sigs in tune. And the Sony only tunes in 1 kHz increments. If necessary I can move the BFO a bit with a small screwdriver.  I just glued the trimmer pot onto the back of the receiver -- two wires covered by heat shrink run back into the circuitry. 

10k might be a bit too small.  Maybe 100k would be better?  As it is, I can move the BFO above and below the "zero beat" point, and I don't need more range. Mouser has a small trimmer pot with a tuning wheel that looks like it might fit, so I may try for a proper repair. 

K.P.S. Kang's Minimalist VXOs (and one for the BITX)

K.P.S. Kang provides us with some great ideas for simple VXOs.  He includes an intriguing reference for a 5 MHz circuit useable in a BITX.  Tell us more OM! 

http://smallwonderqrp.blogspot.com/2017/07/vxos-simple-minimalists-signal-sources.html

NYC's Radio Row Survives (sort of) in the Bronx

Thanks to our friend (and official lexicographer) Steve Silverman KB3SII for alerting us to this important bit of radio news from the Big Apple.  It seems that a part of old Radio Row was saved and moved -- first to Brooklyn and now to the Bronx.   I got a kick out of some of the comments in the New York Times article about the store:  The insurance company determined that the contents of the store were "non-pilferable." And one young audio enthusiast was quoted as saying that old American tubes "sound better" than Chinese tubes.  I guess they have more presence.  Or brightness.  And less feathering.  Or something.

Here is the 2011 NYT article: 
http://www.nytimes.com/2011/11/20/nyregion/leeds-radio-is-a-haven-for-lovers-of-all-things-analog.html   


To N2CQR  

Jul 17 at 12:26 PM

Bill

Radio Row survives in a storefront in the Bronx, by appointment only.  Leeds Radio was started in 1923 and survives because an enterprising customer bought it from the 72 year old owner.

But this is where you can shop any time for stuff that should be in your junk box:

https://www.etsy.com/shop/LeedsRadio

Yikes, what is the world coming to?

I promise to keep any information about what you actually buy on that site a secret!

73

Steve  KB3SII  ... .. ..

PS  When I was 11 (and WN1ZPT) , my parents visited NYC and gave me $10 and sent me alone on the subway to the real Radio Row.  I was in heaven for a few hours!  Got good stuff too.

Excellent Description of the Electret Microphone

I've been experimenting with electret replacements for the D-104 crystal element.   I found this site with a really excellent description of what lies inside those little electret capsules.  Here it is: 

http://www.openmusiclabs.com/learning/sensors/electret-microphones/index.html