Very dangerous, but that's the they built radios back then. Everything was open, you could grab a hand full of electrons real easily !
Bill Sent from my iPhone > On Nov 23, 2014, at 10:45 AM, Chuck Forsberg WA7KGX <c...@omen.com> wrote: > > >> On 11/23/2014 08:31 AM, Bill Guyger via FlexRadio wrote: >> A couple of separate answers: >> - Capacitors in series do roll off the lows, but if you pick a cap whose >> reactance at one octave below the lowest frequency that you wish to be >> "flat" is equal to the reactance (though you can probably get away with >> simply using the DC Resistance of the headphones for all practical >> purposes...) of the phones, the frequency response will be 3 dB down at that >> frequency but will be back to flat at one octave above the "corner" >> frequency. So if you assume a lowest desirable frequency of 300 Hz. for >> communications purpose pick a corner frequency of 150 Hz. >> - And back in the day (1920's - 1930's) the voice coil of the speaker was >> used for the filter choke, and if you look at old radio schematics, say in >> the ARRL Handbook, you will see the headphones in series with the B+ for the >> amplifier tube. But that went the way of the Dodo when transformers became >> more readily available. >> Most high end amplifiers either use a transformer, or in the case of >> transistor amps have complimentary output devices with B+ and B- supplies so >> (in theory) there is very little DC at the common point the speaker is >> connected to. If you do loose one side of the power supply the full tilt >> boogie voltage of the other supply will be applied to your speaker and you >> have a good chance of blowing the voice coil.I have literally seen a speaker >> cabinet catch fire and burn because the amp went into DC. High quality amps >> have protection circuits to prevent that, but the Certain Vagrant (Cerwin >> Vega) amp that caused the fire did not because Vega was really cheaply >> designed. >> Bill AD5OL >> From: Rob Keijzer <pa3...@amsat.org> >> To: Bill Guyger <bguy...@yahoo.com> >> Cc: flexradio <flexradio@flex-radio.biz>; Mike Sonn >> <fatfend...@sbcglobal.net> >> Sent: Sunday, November 23, 2014 7:34 AM >> Subject: Re: [Flexradio] Flex 5000A w/earbuds >> There is indeed dc on the 5kA phones output. >> When I plug in a headphone I hear a loud pop (almost to the >> level it makes me think it'll be blown). >> >> I asked once why on earth this is needed, and got the answer that >> blocking this DC (by transformers or capacitors) would also block >> the lowest audio frequencies. >> >> >> I simply don't use the headphones output. >> BTW: I never heard that high end audio required our equipment to run DC >> through our voice coils. >> >> Rob, PA3CNT >> >> 2014-11-23 5:06 GMT+01:00 Bill Guyger via FlexRadio >> <flexradio@flex-radio.biz>: >> >> Forgot to add grab a voltmeter and check for DC >> >> Bill >> >> Sent from my iPhone >> >>> On Nov 22, 2014, at 10:04 PM, Bill Guyger via FlexRadio >>> <flexradio@flex-radio.biz> wrote: >>> >>> Heating in headphones and speakers is usually caused by D.C. coming out of >>> the amp. I underline usually maybe something I'm not considering though..... >>> >>> Bill AD5OL >>> >>> Sent from my iPhone >>> >>>> On Nov 22, 2014, at 8:27 PM, Mike Sonn <fatfend...@sbcglobal.net> wrote: >>>> >>>> Anyone else use earbuds? I've used a set for years with my Flex 3000. I >>>> now have upgraded to a FLEX 5K and when I stuck my earbuds in for the >>>> first time, they were very warm. I thought I had them leaning against >>>> something warm in the shack, but after sitting on the desk for 10 >>>> minutes, they are still warm. My ear canals won't get cold, but >>>> clearly, there's something strange going on here. Any ideas? >>>> _______________________________________________ >>>> FlexRadio Systems Mailing List >>>> FlexRadio@flex-radio.biz >>>> To opt out of the Reflector: >>>> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> >>> _______________________________________________ >>> FlexRadio Systems Mailing List >>> FlexRadio@flex-radio.biz >>> To opt out of the Reflector: >>> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> _______________________________________________ >> FlexRadio Systems Mailing List >> FlexRadio@flex-radio.biz >> To opt out of the Reflector: >> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >> >> >> >> > In the old days the loudspeaker used a "field coil" instead of a > permanent magnet. The B+ supply had a capacitor input, > then the field coil, then the rest of the radio. A hum bucking > winding was sometimes used. > > I don't know of any radios that had B+ on the headphone terminals. > A bit shocking I'd think. > > -- > Chuck Forsberg WA7KGX c...@omen.com www.omen.com > Developer of Industrial ZMODEM(Tm) for Embedded Applications > Omen Technology Inc "The High Reliability Software" > 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > To opt out of the Reflector: > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz To opt out of the Reflector: http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
