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MG TD TF 1500 - Tube Radio Help

Hi:
I just bought a tube Motorolla 400 to try to fit it to my TF. The radio has 2 black wires comming out of the back wih no indication as to + or -. What happens if I hook them up wrong? Will the radio blow up, burst into flame or just not work? Please remember that I am electicaly challenged and can not understand why current does not run out of the wall sockets and get me by the foot when I walk by.
Godspeed in Dafety Fast
Jc
John Crawley

I would suspect that a tube tupe radio is polarity insensitive, therefore no polarity indication on the power leads. The tube filaments use the 12V DC for heating so don't care about + or -. Thr other voltages use are derived from DC to AC conversion, a transformer, to get the high voltage, and then rectified back to high voltage DC. (Would expect 50 to 150 volts DC for typical tubes).

Solid state radios simply do a DC viktage divider to get the typical +5 volts, and are thus polarity sensitive. Reverse polarity = smoke!
Don Harmer

All the old radios I put in various cars (in my youth) would have three wires... a power wire, and a +/_ speaker wire. If there wasn't a power wire (with a fuse), there was a plug of some kind for the power....! Check for any little pluglike spots or screws marked +/- for the speakers.
gblawson - TD#27667

John,
On old radios ...I have found same as Gordon says.
One other suprising thing I have found about some old "tube" equipment:
Take a digi picture and "google" the maker ...get their address and send them the picture & a nice email.
(I say "digi" pic because when I googled "Motorolla 400 Radio" it came back with several "newer 2 way radios that share that model number now!)
I have had several of them send old manuals back in PDF form (if they have them scanned) ...and a couple of times I have even had them send me an old manual!
Very cool when that happens!
Good Luck,
David 55 TF1500 #7427
David Sheward

John

I think that you will find that your motorola 400 is a 6 volt radio. here is the schematic.

http://www.nostalgiaair.org/PagesByModel/580/M0006580.pdf

John
John Scragg

Hi All:
WOW what a great group and I ever glad that I asked!
The schematics that John Scragg sent are exactly for the radio that I have. I will try to power it up with a 6-volt battery charger and see what happens. It will be a good trade item if it works but will not go into the TF.
Thnaks again.
Jc
John Crawley

John -- If you power your radio with a battery charger only you could possibly do some damage to the vibrator. Put large electrolytic capacitors across the output of the battery charger to smooth out the waveform.

I would just guess that with the 6 volt tubes shown in the first schematic, (6K7,6K6 etc) that the B+ voltage would be closer to 250 volts than the 150 mentioned above. By now all the wax paper capacitors will probably have to be replaced, they get leaky and their series resistance goes up. Also the electrolytic capacitors in the power supply have probably dried out and should be replaced, if so you will get a horrendous buzzing in the loudspeaker. Hopefully the tubes are all OK they are getting hard to find nowdays.

Godd luck and keep me informed of your progress in firing it up.
Cheers
Bob
R. K. (Bob) Jeffers

This thread was discussed between 04/03/2007 and 05/03/2007

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