The AM Forum

hi guys I recently picked up a 5100b on epay,I have a few problems its been retubed and recapped except for the line filter cap oil can..
here are a list of problems any suggestions would be appreciated.
60 volt ac from chassis to ground.
relay energizes delayed.
I got a rf burn when ground was not connected  on the front toggle switch.
low output 30 watts.
Thanks in advance
Mike KA1CU Woodbury,CT

lookit the line filter cap. they do go bad. Otherwise suspect a transformer case or winding leak to chassis or primary to secondary short.

You're going to get 60VAC on the chassis whether the line filter caps are good or leaky.  Remember they're arranged as a voltage divider across the line with the chassis being the center.  The current will be small due to their relatively high reactance at 60 HZ but it's always a good idea to replace 'em.  And it's a great idea to replace the line cord with a 3-conductor, grounded one.

You always need to provide an RF ground for the transmitter, or you're liable to get an RF burn off the thing depending upon your antenna setup.

Relay delay:  I dunno.  Look at the schematic and figure out what might cause it.  Could be a mechanical issue with the relay also.

Low output:  If you're tuning according to the book and getting the right plate current reading, I'd suspect the loading caps, coupling cap(s) from the plates to the pi-network, or a parasitic.  You should verify that the plate current meter is reading correctly.

I would suspect though since the rig is new to you and in "as found" condition you're not tuning it up correctly, or someone's gone in and perhaps messed with something.  Some xmitters can tune up on a harmonic.  Example, if you tune the driver up on a harmonic but try and tune the plate for  the fundamental, you'll never be able to obtain full output.  If you can't make the rated plate current and your tuneup procedure is right, I'd suspect the finals and/or driver tubes.  Or the HV rectifier is gone, giving low B+.

I had a low power out with my 5100B. Found that the 6.3 volt filament supply was actually 4.7 volts. I found a 6.3v transformer and cut the 6.3v leads from the factory transformer and then connected the new transformer to the leads cut off from the original transformer on the side going to the filament string. Not sure that is your problem but check your filament voltage. I was able to use some Goop and adhear the new transformer to the top of either a choke or another transformer under the lid I forgot which one it was. Also I ran new 120vac leads from where the original leads come into the original transformer to the new transformer..

5100b update.
Low power, rf burns............ solution bad doorknob cap on final
delayed relay  operation ............clean and lube relay pivot points
thanks to all .I look forward to chatting on 75/80 AM

Mike KA1CU Woodbury,CT