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M WARD farm radio 54kp-1209b - Printable Version

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M WARD farm radio 54kp-1209b - David - 02-25-2016

Purchased this radio in 2006 never could get it to work right. When I get in the mood I will do some more work on this thing. All caps and out of spec resistors replaced.  First thing never use a AAA battery for A battery for testing. This set likes a couple of D cells to supply 1.5 volts for the A battery.   For the B battery using the power supply design on Phils old radios web site.  http://antiqueradio.org/bsupply.htm  The no load voltage 94VDC with radio on reads 84-83VDC. Replaced the fellowing tubes with NOS 1H5GT, 3Q5GT all other tubes checked by using NOS sub no change in performance. Replace the speaker and output transformer the orginals were trash. Now to the problem if I connect a ground get a very loud buzzing sound. If I disconnet the outside ant coil from the chassie and use a ground to the outside ant coil big improvment in reception. http://www.nostalgiaair.org/Resources/231/M0011231.htm  At this point very happy with the radio just do not understand what is happening with the ground. David

RE: M WARD farm radio 54kp-1209b - Mondial - 02-25-2016

If you are using the power supply design shown in the Phils Radios link without an isolation transformer, you have created a very dangerous condition. 

The ac line is directly connected to the radio chassis, so connecting the radio to an external ground is a problem. You have created a hot chassis set. Do not connect anything external to the radio without an AC isolation transformer!


Read the caution in the power supply instructions regarding the use of an isolation transformer. Its the only safe way to use this power supply with external antenna and ground connections.

RE: M WARD farm radio 54kp-1209b - David - 02-25-2016

Thanks for the warning, so this thing is going to try and kill me. David

RE: M WARD farm radio 54kp-1209b - David - 04-01-2016

   
I would like to build a better power supply that does not require a seperate isolation transformer. The one I am building for the A battery supply contains a LM317 showing three diodes on the output instead of a small cap? Could someone please explain this to my simple mind. David

RE: M WARD farm radio 54kp-1209b - Mondial - 04-01-2016

The diodes are most likely there for protection. 

If the regulator LM317 should short, it would put the full unregulated DC voltage into the 1.4V filaments of the tubes, instantly blowing them out. The three diodes effectively clamp the output voltage to a max of 2V or so, thereby protecting the filaments from possible destruction in case of regulator failure.

RE: M WARD farm radio 54kp-1209b - TV MAN - 04-01-2016

I think Phil's power supply would be ok for portable radios that are in plastic cabinets an such. I believe this is what it is designed for. In the older wooden cabinet radios, there are exposed chassis, screws, maybe knobs with set screws that you could touch. Probably not a good idea to use next to the bathtub. Icon_rolleyes  Polarized plug would help, but Mondial is right in that you could have a hot chassis. Depends on how the plug is connected.

RE: M WARD farm radio 54kp-1209b - mikethedruid - 04-02-2016

David, if you are building the supply in the schematic you posted, I see nothing wrong with it, really. All the voltages to the radio itself are isolated by being separate windings on the transformer.

RE: M WARD farm radio 54kp-1209b - fifties - 04-03-2016

I have several farm sets, including a Motorola and, *gasp* a Philco! With both of these, I use a string of 8 to 10 nine volt batteries for the plate circuit, and one D cell for the heaters.

Connected to my outdoor random length long wire antenna which uses RG59 coax as the lead in, I get no household AC interference; great for DXing!