I am interested in starting some sort of new thread here on people's experiences with mini-broadcasters used to broadcast tapes, CDs, FM, or whatever in the home to our restored old radios. I need such a device, and so does a friend. I know there are several for sale as kits. Some are based on old designs, others are solid state. A helpful e-mail exchange with one gentleman through this BB answered some questions, and raised others.

So, what does one look for? Do the one-tube jobs really not "work so well"? Does the solid state stereo version really "act up" with some CDs? How well are the program source devices protected? And above all, how's the audio? Won't a modulated oscillator require slope detection (giving limp audio)? Comments?
Thanks,
Jim

Hi,
The simple one tube units work fine, but you may need to use transformer coupling to eliminate some potential issues of ground loops, phasing as related to major "hum" issues.

The solid state units work fine too. Some of the problems that may have been encountered by others were the result of impedance mismatch, being too close to a switching power supply, or other EM interference.

As far as the radiated signal is concerned, it is low power, some are actually a free radiating low power transmitter, and some also use the house wiring as the transmitting antenna (talking house). No special recievers are needed for the most common types. Heath made some that required a special reciever to hear the signals.

As for sound quality, most of the old radios were not "Hi-Fi" (They sound good, but they are not usually designed as "Hi-Fi"), but even the for the midgets, the music output will usually be very good quality. Too many people mistake THD figures in todays solid state amps for the level of noise at zero signal input- These are two totally different animals, and in true fact, second order Harmonics and to some extent fourth order harmonics are the THD that give tube amps their "tube sound". But in general, do not expect to have the same performance characteristics for your vintage radios as you would expect from your home stereo playing CD's that were mastered from DDD sources.

There is a good place to check on the simple transmitters,

One is a review of the AES kit: http://antiqueradio.org/transmit.htm

The other is a simple project that Phil gives a little history about: http://antiqueradio.org/lil7.htm

: I am interested in starting some sort of new thread here on people's experiences with mini-broadcasters used to broadcast tapes, CDs, FM, or whatever in the home to our restored old radios. I need such a device, and so does a friend. I know there are several for sale as kits. Some are based on old designs, others are solid state. A helpful e-mail exchange with one gentleman through this BB answered some questions, and raised others.

: So, what does one look for? Do the one-tube jobs really not "work so well"? Does the solid state stereo version really "act up" with some CDs? How well are the program source devices protected? And above all, how's the audio? Won't a modulated oscillator require slope detection (giving limp audio)? Comments?
: Thanks,
: Jim

Thanks guys. John, the AES rig review was helpful. Since my friend who needs one of these little rigs would be operating it in the world's worst noise environment (lighting), I figure the AES xmtr is a little limp. Thanks also for the tips on xfrmrs/isolation.

Dean, I am headed to the newsstand tomorrow. Probably have the original article in the attic somewhere (I know Herb Brier's articles are there), but why brave the bats when I can test drive the new incarnation of PE? Thanks again guys.

Anyone else want to weigh in?

73, Jim

Jim, back in the January 1965 issue of "Popular Electronics", "The Wireless Re-Broadcaster" construction article was published. It used a single 12AT7. I built the circuit back then and it had excellent performance. The bass response was wonderful, really accenting the rich bass of the old radios.

I reprinted that schematic in my "Q & A" column in the March 2002 issue of "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines. You should be able to find that issue on the newsstands now. The schematic did publish with a glaring error in the heater circuit off the 6.3v secondary of the transformer, showing everything as a massive dead short. One side of the secondary should go to pins 4 and 5 of the 12AT7, and the other side of the secondary should go to pin 9.

If you can't find that issue (it just came out and should remain on the newsstands for at least a month), let me know and I'll e-mail a skem to you. There will be a reader's comments and suggestion on that circuit appearing down the road in the June 2002 edition of the "Q & A" column.

Dean

q&a@gernsback.com
dhuster@pb.k12.mo.us
dhhuster@semo.net
http://www.gernsback.com