The AM Forum

for most of you this will sound like 'preaching to the choir' but as I qso with boat anchor owners, it surprises me how many never think of this ....

most old transmitters with more than one power transformer (Johnsons, Heaths, etc.) have only one fuse in the 60 Hz supply and it is sized for total power consumption.  example: Johnson Viking II - 5 Amp

the smaller power transformer can under fault conditions therefore be overfused and subject to burnout

the solution is simple : add a fuse for the smaller transformer (generally 1 Amp or so) use a clip in holder which is available for a buck or so and double side tape mount it for those unwilling to punch / drill a mounting hole

please do this !!!  original iron is mostly gone/ used up because of this problem ... thanks  .. 73  John

John,

A good reminder.  I almost had the dubious pleasure of replacing a lot of wiring harness on a Viking 1; the reason for failure was a shorted base in a replacement for the power indicator lamp.  I turned on the transmitter and immediately saw the vinyl insulation on the 6.3 V wire in the harness start to melt and I killed the power before any damage to the transformer or other wires. 

I use inline fuse holders as my way of avoiding drilling holes.  For those that insist on staying with the original dual fuse plugs for the Johnson and early Heathkit gear there is a safety hazard if the fuse in the neutral side is the one that blows.  The neutral side of the line is not supposed to be interrupted with a switch and/or fuse.  I have converted most of my rigs over to 3 wire grounded plugs but if you want to keep the original plug while increasing your safety, check your power outlet and confirm that the neutral side is properly connected to neutral and then mark the plug clearly which side is neutral.  Then make sure the proper sized fuse to handle the transmitter load is in the hot (line or load or whatever term you prefer) side of the plug and replace the neutral side fuse with a 20 to 25 amp fuse; this way the hot side fuse should always blow before the neutral side.  IF you use these plugs get "religious" about the old safety rule of ground is the first thing you connect to the rig and the last thing you disconnect.  Let's keep the rigs glowing and the owners not!

Rodger WQ9E

when you are at a fester, look for the old littelfuse # 356 holders in dual and single configs. I'm putting one in the Gonset and I'll snap a pic.

The photo is from an SX-101A I just put on the bench, definitely a different kind of fuse holder!  This was added to protect the "damp chaser" resistor and I would call it a fast change fuse holder except that the two clips were heavily wrapped in tape.  Another interesting touch was the change to a solid state rectifier through soldering a couple of diodes to the base of the 5Y3GT socket with no additional dropping resistor. 

These will get corrected along with the replacement of a number of black beauty caps.  I picked the SX-101A up along with a Viking 1 last month for $100.  The Viking 1 just needed a few new caps and it is sounding good.  I do need to find a knob to replace the missing antenna trimmer knob on the SX-101A but otherwise it is cosmetically in good shape and has the calibrator mounted inside.


Rodger WQ9E