Globe 500C owners.

[ke7trp]

While performing round 2 of the mods to my now working 500C, I loaded it up and found 300MA and about 220 to 250 watts AM on the Bird into a Dummy.  The manual says to load to 330.. But it will not make it. 300 is the max I can load this transmitter to.

I have about 1800 volts on the plate according to the manual. I dont have a meter high enough to test this. All tubes have been checked. I swapped in a spare 4-400 but it was a BC pull as is the tube in there now. Abou the same outpoot.

I would like to know what 500C owners are seeing in real world as far as output goes. This one seems rock solid with proper, OSC, Buffer, Grid and Screen current. INput is rated at 540 watts on the C model.  I would think this would be 300+ on AM.

If this is normal, I am done. I just need to install the w0VMC audio mods to the Mod deck and I need to repaint the chassis. I have used the radio for nearly a week everyday with no trouble. I have a feeling the 4-400 is weak. If it is, I will need to source one. All other caps, voltages have been checked.

Thanks for the help.. What does your stock to nearly stock 500C produce on AM?

Clark

[Detroit47]

Clark

I had a 500c in for a repair last week. I couldn’t get the plate current up to 330 only about 275, and I had plenty of grid drive. It turned out the screen voltage was low. I replaced the filter caps in screen circuit, and the result was full plate current. I would check the screen voltage on the final first.

 73 Johnathan N8QPC

[Jim, W5JO]

A couple of things you don't mention.  1.  What kind of wattmeter and how accurate it is.  2.  What kind of antenna situation.

My 500A (same circuit) loads to 330 ma. very easily into the proper 50 ohm load.  It is most efficient at @ 300 ma. so that is where I run it.  Power output is 325-350 watts on 80 meters.  In fact, I can load to nearly 400 ma.

Best check those step capacitors attached to coarse load switch.  If one or more are open, (I have seen them with cracked cases or the value was significantly off) then loading may not work like it should.

[ke7trp]

I am using a bird 43 meter.  I have a 500 and a 1000 slug. Both read the same. The dummy load is a heath can tenna. Same power out on my antenna as is the dummy. 

I have checked all the loading caps. They look perfect. I have not checked them with a meter though. they do increase as I change the loading control.

Screen current is by the book. I will check screen voltage and let you know what it is.  Its probably just a weak 400 tube. I wish I had a new 4-400 or at least a known good one to test.

This thing will load right to 280 or so.  Its happy to run along at 220 watts am. 

C

[ke7trp]

I think you nailed it.. Screens volts is 300.  Missing 100Volts.  Going to have to dig into this thing a bit harder I guess. Still cant measure plate voltage as my meter wont go high enough.

Clark

[Detroit47]

Clark
I have found that the plate voltage usually isn't the culprit. If the oil filled cap is ok and both of the rectifiers are ok you should be good to go. I have had to replace the plate transformer on two Globes. But if the plate transformer goes bad it won’t be a secret.

73 N8QPC

[ke7trp]

Ok. Replaced Screen  electrolytic caps.  Put in 2.2s in place of 55 year old 2mfd caps. Also put in a 001 at 3500 volt cap from Screen bar to Ground. The old one was a 005 disk cap. Looked burned.

Found a Crack in the Door knob from 6146 to 4-400.  Cracked pretty bad.. Old was an 850 and new one was 1000P at 5KV. 

Now I have more Grid drive. Before, I had to run the control nearly maxed. Now to get 15 ma of grid and I need only 3 on the control. I can now load to 300 MA solid on 75 meters. I am now at 300 watts out with 100% mod. Sounds clear on the monitor reciever. I can load higher but I have to cross over 15 ma of grid drive and they say not to do that in the manual.

I can only guess that now, I am at full power with this 4-400.  Its a broadcast pull and the plate looks Brown and has heat waves in it. I ordered a New and tested full output 4-400 from W0VMC.  I hope to swap it in and get 330 ma and 350 watts. Even if it stays the same. 300 watts is not bad I guess! Heck, I started with 200!

Also, this is from a 15 amp wall socket on the bench. THis will normaly plug into its own 30 amp supply.. THis supply is across the room and I cant plug it in unless I move the GK into is final resting spot. Maybe it will come up more on the 30 amp line.

Now on to the Modulator deck.  By by couplates!

Clark