Globe Champion 300 Transmitter

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Gary L. Carson:
Hi--
This is my first time here....Bought a Globe Champion 300 on Ebay to use for vintage AM use. Seller didn't know any history on it, as usual. Cleaned it up as much as possible, replaced all electrolytic and paper caps (except the big oil-filled HV filter cap) with new parts. Noticed signs of arcing from the 866A rectifier sockets to the chassis, so I replaced the sockets with new ones that don't use retaining rings. I mounted them so as to provide a little more space between the conductors and the chassis.

Powered it up, then had to replace a relay that was buzzing. Oscillator/exciter stage seems to be working, can be heard on receiver. Proceeded to try to tune it up into a dummy load. a few seconds after the HV is turned on, the filament pins on the rectifier sockets arc to ths chassis, over about a 1/4 inch path. Time to check a few more things.

I don't yet have a meter that will safely read the HV directly to see what  it is climbing to. Am going to attempt to test the value of the big filter capacitor to see if it has changed over the years. I have a Fluke DMM that can measure capacitance, will try that.

I am fairly new to boatanchors, and don't own a lot of test equipment, at least not yet. I also don't have the experience that many hams do when it comes to older gear. I am learning as I go, and being very careful with the HV stuff. I don't want to destroy any hard-to-get parts by powering this rig up until I can find the source of this problem.

Was wondering if any of you have encountered this problem before. I know That I can eventually track it down, but am open to any input as to the solution. Would appreciate any advice you all might be able to give.
Thanks;
Gary

Allen C. Ward:
Make sure that your new sockets can take the voltage level.  When you solder to pins (or anything else)where there is high voltage, make sure that the joint is rounded and has no sharp points.  In other words a smooth globular joint.  Cover the actual joint with shrink tubing or corona dope.  
High voltage can cause a corona discharge which can ionize the air and allow an arc over.  So insulate the connections.  If the sockets were bad you should be able to see a carbon path burned into the insulating material.  The retaining rings probably had nothing to do with the problem.
Allen

Gary L. Carson:
Hi--
Thanks for the reply. When installing the sockets, I tried to keep the connections as round as possible. The sockets on it now have rivets just outside the pin receptacles. The arc is between one of them and the chassis. I had relieved the chassis slightly with a die grinder in the area of the pins, to allow about 1/4 inch clearance. I didn't want to alter the transmitter any more than necessary in case I ever want to sell it to "upgrade". Seems like any deviation from normal appearance reduces the value of older gear, although I don't have a problem doing mods if they are necessary to make it work right.

I have considered mounting the sockets on a rectangular piece of insulating material such as PC material or formica, then neatly cutting a slightly smaller  area out of the chassis to mount it. Before I do anything like that, I need to find out if anything else is causing this problem. Did measure the filter cap last night, it shows 5.75 MFD, rating is 6 MFD. Guess I need to improvise a way to measure the HV next, in case it is way too high. Don't see any opens between the power supply and the PA or modulator stages, and the panel meter shows plate current when trying to tune before the arcing starts up. Don't want to destroy the PA tubes (if they are still OK), since they are about $125 each, when I can find them for sale.

I have absolutely no history on this rig--don't know if it ever worked at all. These were also sold as kits, however I naven't found any wiring mistakes so far. When I replaced the caps, I had checked them against the schematic for proper polarity, value, etc. Everything looked OK, but the entire radio has not been checked for that type of thing. Will keep digging as time permits.

Allen C. Ward:
Have you checked the bases of the tubes?  There might be a carbon path on one or both of the tube bases.
Allen

Gary L. Carson:
Hi Allen--

Thanks again. Looked at the tube bases once, will do so again, this time in better light, etc. The old sockets did have blackened "tracks" on the ceramic, which could not be cleaned off completely. I tried cleaning the old sockets, but it arced the first time I tried to tune it. That's when I replaced them. Have also considered replacing the 866A's with diode strings. Bought the diodes, feed-thru insulator and all. That will raise the B+ voltage even more; probably not the thing to do right now. Am going to inspect things all over again, then see if I can measure the voltage coming from the plate transformer. I guess I need to invest in a meter that can handle higher voltages. DMM's rated 1000, VTVM 1000, FETVOM rated 1500. If the transformer was to have primary turns or layers shorted, voltage might be way higher than the 1000V its supposed to be. May use resistors to scale the VTVM higher.

Thanks for the tips;
Gary

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