UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions
Register FAQ Forum Rules Calendar Mark Forums Read

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Reply
 
Thread Tools
Old 10th Jan 2011, 10:02 pm   #1
JHGibson
Hexode
 
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 332
Default Battery-less audio amplifier

Being a hard-core crystal set builder, I was delighted to read about a battery-less audio amplifier. It used a second crystal set peaked on a local station to charge up a 0.3 FARAD cap. It took most of the day to charge it up to some 1.5 volts , but that was sufficient to run a micropower op amp drawing a microamp for 3 hours.
For details see article 25 on
www.bentongue.com/xtalset/xtalset.html
John.
JHGibson is offline   Reply With Quote
Old 11th Jan 2011, 11:48 am   #2
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Witney, Oxfordshire, UK.
Posts: 6,925
Default Re: Battery-less audio amplifier

There's a certain elegance about the idea, but in practical terms, unless you want to listen in the dark, a simple solar cell power source would be more effective I reckon. Probably cheaper, too, unless you can use all junk box components for your PSU receiver.
__________________
.........._______
.....___/|__|__|\____
.=.( _---\__|___|_---_)
.........O...Chris....O
Herald1360 is offline   Reply With Quote
Old 11th Jan 2011, 12:01 pm   #3
Coastwatch
Pentode
 
Coastwatch's Avatar
 
Join Date: Feb 2010
Location: Berwick-upon-Tweed
Posts: 113
Default Re: Battery-less audio amplifier

The one I built in the 60's, a PW design I think, had the power supplied from a LW Xtal set with 4 diodes (can't remember which [OA91]) as a bridge rectifier.

Now does anyone remember the WWII spy transmitter that used no power supply. I will start a thread on that one soon.
__________________
Ouch! who turned that soldering iron around
My other hobbies
Coastwatch is offline   Reply With Quote
Old 11th Jan 2011, 12:02 pm   #4
kalee20
Nonode
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 2,919
Default Re: Battery-less audio amplifier

Both these approaches have this in common - they use EM energy from another source to provide power. Only Herald1360's approach uses energy from somewhat further up in the frequency spectrum.

Of course, to keep on-topic, you could only use one solar cell, else you'd have a (solar) battery.

Micropower operation is fascinating, however I'd guess that the micropower op-amp could not drive more than a crystal earpiece without significantly increasing its power demand.
kalee20 is offline   Reply With Quote
Old 11th Jan 2011, 12:24 pm   #5
ajs_derby
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 3,647
Default Re: Battery-less audio amplifier

A solar cell is less likely to get you into trouble with anyone, as well! (Someone paid for the energy that went up that transmitter mast, and they might well take a dim view of anyone using more than their fair share of it. It would hardly be the silliest thing anyone's ever been prosecuted for.)

At least, until daylight is privatised .....
__________________
AJS

Please use this thread for free valuations on kit you want to sell elsewhere.
ajs_derby is offline   Reply With Quote
Old 11th Jan 2011, 3:52 pm   #6
G8HQP Dave
Nonode
 
Join Date: Sep 2008
Location: St Neots
Posts: 2,728
Default Re: Battery-less audio amplifier

The modern name for this is energy harvesting, and people are looking at it as a way of powering remote sensors etc. Whether the broadcasters, mobile phone firms etc. are happy about this remains to be seen.

The danger I see is that as well as extracting energy which was meant to end up in the front-end of a receiver (so possibly reducing range for legitimate users) it could also radiate interference (rusty bolt effect on a big scale if everyone starts doing it).
G8HQP Dave is offline   Reply With Quote
Old 11th Jan 2011, 4:33 pm   #7
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Witney, Oxfordshire, UK.
Posts: 6,925
Default Re: Battery-less audio amplifier

Quote:
Originally Posted by ajs_derby View Post
It would hardly be the silliest thing anyone's ever been prosecuted for.....

ISTR "stealing Post Office electricity" was the only charge that would stick in a '70s phone hacking trial.

Back with harvesting, I suppose if you can get 500mV into 50R with a decent antenna, that's 5mW which could be quite useful. Some cleverness with fets could step it up to a useable voltage too.
__________________
.........._______
.....___/|__|__|\____
.=.( _---\__|___|_---_)
.........O...Chris....O
Herald1360 is offline   Reply With Quote
Old 11th Jan 2011, 4:44 pm   #8
G8HQP Dave
Nonode
 
Join Date: Sep 2008
Location: St Neots
Posts: 2,728
Default Re: Battery-less audio amplifier

I seem to recall that "dishonest use of electricity" was threatened against people who would signal to the wife that they had just arrived back at the railway station, by doing two rings from the call box.
G8HQP Dave is offline   Reply With Quote
Old 11th Jan 2011, 5:51 pm   #9
KeithsTV
Octode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford
Posts: 1,497
Default Re: Battery-less audio amplifier

When I lived in South Birmingham I was about 8 miles from the Droitwich transmitter and with 100ft of wire as an aerial and a decent earth I could get 1v dc, as indicated on my multimeter, from a crystal set tuned to 200kHz.

Keith
KeithsTV is offline   Reply With Quote
Old 12th Jan 2011, 9:18 am   #10
davegsm82
Heptode
 
davegsm82's Avatar
 
Join Date: Jan 2004
Location: Blyth, Northumberland
Posts: 833
Default Re: Battery-less audio amplifier

I've tried to do this before, it never worked particularly well.

In the early 90's (possibly late 80's?) I made a crystal radio from some old cheap chinese AM transistor radio, I put a battery snap (pp3) on the earth and connected this to the radiator. I was astounded to find it didn't need an aerial! The ferrite rod inside was enough. Used to listen to Radio1 on that late into the night, until I got bored or fell asleep and rolled my ear over onto one of those horrible crystal earpieces!

Interestingly, now that I have my own home i've been experimenting more, when I moved in we removed the old gas fire but left the aluminium flue in place, this is insulated from everything by brickwork. Measured with a fluke 175 there is about 500mV DC with respect to earth on it at all times, even after breifly shorting it out. Works quite well as a CB aerial too!

Have a look here, from what I can tell, these crazy russians aren't playing with a live transmitter, they're playing with a disused antenna not far from a transmitter, just look at that spark!...

http://englishrussia.com/index.php/2...-plasma-radio/

Dave.
davegsm82 is offline   Reply With Quote
Old 12th Jan 2011, 7:32 pm   #11
JHGibson
Hexode
 
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 332
Default Re: Battery-less audio amplifier

Getting back to the original post, reading Ben Tongue's article 25, the procedure seems that you leave the crystal set tuned to a strong local station when the receiver is "off" and the 0.3 Farad cap will charge up. When the crystal set is "Turned on", the now fully charged 0.3 F cap can run the micropower opamp for some 5 hours and that 20 db of gain really helps. 5 hours of listening time is plenty! No need for additional parts like photo voltaic cells.
John.
JHGibson is offline   Reply With Quote
Old 13th Jan 2011, 6:20 pm   #12
Andrew2
Heptode
 
Join Date: Mar 2010
Location: Cheshire, UK.
Posts: 646
Default Re: Battery-less audio amplifier

Back in the 60's there was a company that advertised all manner of odd projects in the back of PE and PW. My mate Pete bought a couple - one was a micro radio powered by a voltage-doubling crystal set and the other was a radio which got its ergs from rotting bread. They worked...just.
__________________
Andy G1HBE.
Andrew2 is offline   Reply With Quote
Old 13th Jan 2011, 6:48 pm   #13
Biggles
Heptode
 
Join Date: Feb 2004
Location: Hexham, Northumberland
Posts: 709
Default Re: Battery-less audio amplifier

Would it not be better to build two crystal sets (or more) and connect their outputs in series to make a very loud crystal set?
Alan.
Biggles is offline   Reply With Quote
Old 13th Jan 2011, 7:26 pm   #14
dseymo1
Octode
 
Join Date: Dec 2007
Location: Shropshire, UK.
Posts: 1,164
Default Re: Battery-less audio amplifier

Quote:
Would it not be better to build two crystal sets (or more) and connect their outputs in series to make a very loud crystal set?
Trouble is, most crystal sets produce their output WRT earth, so they could only be connected out of phase, producing a null o/p
dseymo1 is offline   Reply With Quote
Old 13th Jan 2011, 7:35 pm   #15
murphyv310
Banned
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire (Burns Country)
Posts: 4,160
Default Re: Battery-less audio amplifier

How about synchronous detection using schottky diodes?
murphyv310 is offline   Reply With Quote
Old 13th Jan 2011, 8:55 pm   #16
JHGibson
Hexode
 
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 332
Default Re: Battery-less audio amplifier

A micro power RF stage powered from the charged 0.3 Farad cap would be a useful addition to the crystal set. Stronger audio from weak stations and faster charging of the 0.3 F cap when the set is "off". Sounds like a perpetual motion machine!
John.
JHGibson is offline   Reply With Quote
Old 14th Jan 2011, 9:31 am   #17
G8HQP Dave
Nonode
 
Join Date: Sep 2008
Location: St Neots
Posts: 2,728
Default Re: Battery-less audio amplifier

You could connect two crystal sets in series, provided you reversed the diode in one of them. You would need two antennas, and a minor rethink of the arrangements for impedance matching of the output.

If the antennas were really large, so extracting a serious proportion of the available energy, then you might do better to arrange them as a beam instead. Otherwise they might simply share the energy between them.
G8HQP Dave is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 4:21 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at http://www.vintage-radio.net.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright ©2002 - 2014, S&P Technology.