The AM Forum

Hey everyone,

I just got a desk Kilowatt and I am having troubles tuning her up. I wanted to know if someone had a video of the tune up procedure? I can get the grid current to peak, but it won't indicate any plate voltage. I am also getting a 150 grid current indication. Any ideas of where I should look first? Some one has converted her to solid state rectifiers.

Z,

Welcome to the board.



go here,

http://bama.edebris.com/manuals/johnson/deskkw/

it's in there.

gud luck,

klc

As already mentioned, BAMA has the manual and somewhere there are also several service bulletins. We might need some more info??

Are you using a Ranger as the exciter? Is the octal plug in the back correctly wired?

Reading the manual only 20 mils of grid drive is needed for the Desk KW. Do not exceed if you value the RF final tubes.  ;D

On the top of the RF cubical is a toggle switch for "Plate Power". Use it to adjust the grid drive of the KW RF finals in the off position. This should make the first tune up easier. Switch to the on position to get RF final plate voltage. If everything is good your plate voltage should be in the neighborhood of 1300 volts in the low power position, 2600 volts in the high power position. I'll mention this again, best to review the schematic and check every part, wire, switch, etc before plugging in any rig. There are several items in the high voltage circuit that must be correct before the voltage is there.

Gud luck and report back,
Craig





I

Better late than never, don't be disappointed when you encounter an audio quirk demonstrated to me some years ago when you get everything worked out. At half power it sounds fine, but leave it to Johnson to cheap out in the transformer department, at full power HV sags near 100% modulation, not enough scrote when the modulators draw appreciable current. The result is strange looking positive peaks and muddy audio. Not to worry, 3dB is only half an S unit, but if half an S unit is all you have turn the radio off and go watch TV.  ;D

sounds like half of the sec of the hv xfmr is open or bad rectumfinder ... ohmmeter check called for .... possibly sagging primary supply .... hv reg shud be 10% or so

I do hope you know 1KW plate modulated transmitters are now illegal due to FCC rule changes. (;->)

I believe they are only illegal to be operated at that power level, if the PEP is capped at 1500 Watts, all is OK.

 ;D ;D ;D ;D ;D...….and the kilocycle cops are sure to take you away...…………. ;D ;D ;D ;D ;D ;D

LOL,
Craig

You missed my winky, in the words of Senator Phineas T. Phogbound; That's a... I say... That's a joke, son! However... I helped a ham repair a Collins 20V, move and install a Collins 20V2, later he set up a Gates, all broadcast equipment from mic to a grounded, vertical folded unipole antenna, all run a full gallon unmodulated carrier output on 160M. His last project for 160M was a 10KW Collins operating from a 480V 3 phase supply in his "Cottage of Wattage". Then I've read articles on moving, cleaning, setting up and operating many broadcast beasts on 160, some modified for 75M. Hey, they don't call us AM Gangstas for nothing! So far no rats among us, and no nonsense that would get visits from Uncle Charlie, he has his hands full dealing with 40KW CBers and sending someone we all know and love a letter about testicling on air.

You're right, I did, sorry.