Friend brought over a Maverick 250. Looks like it was converted to 10/11 meters. My problem is, the Tune cap is arcing. Is this a common problem? I was using a 148glt to test with. It does 12w pep. I'm just not sure how to decide it its a cap failure or if its parasitics going on. The arc that I could see was on last plate. It was bent some but I pulled it out so it has same spacing as others. Just wondering if anyone else has run into this. Amp was doing 400-450 pep on my Bird 43P when the failure happened. Looks like 6JE6 tubes for finals. 4 driving 4. I'm not sure what the driver tubes are. Any suggestions? Parasitic chokes look to be factory. Resistors look good but hard to tell since the guy is a smoker. Yuck! Lots of tar.
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Maverick 250
- Thread starter Crusher
- Start date
When I had problems like that with a variable cap arcing like that it was due to the plates either touching, or it had a lot of dust and other crap on them. What I do is what you did, make sure none of the plates touch, and I also take a tooth brush and a piece of thick paper and go in between each set of plates, to remove any contaminants that could possibly get lodged between the plates of the cap. Give that a try and see if you still get the arcing. Doing those two items has always worked for me in the past. Let us know how you get on. 
~Cheers~
~Cheers~
Four 6jg6a driving four 6lq6.
What Exit Thirteen posted usually fixes the problem.
Sometimes those plates in the air variable caps will arc and leave a tract that either needs filed down and or sanded down.
Last resort is to remove the faulty plate from the cap. Or replace the var. cap.
What Exit Thirteen posted usually fixes the problem.
Sometimes those plates in the air variable caps will arc and leave a tract that either needs filed down and or sanded down.
Last resort is to remove the faulty plate from the cap. Or replace the var. cap.
Depends, sometimes on small sweep tube amplifiers like this, you could get away with using FINE sand paper and doing that the other people have suggested. However, I don't recommend it. Once they arc, they have a pitted surface and will do it again. If you sand it down, the surface is still not perfectly flush, and the problem can resurface again. Better to spend the 20.00 and just change it out.
Yeah, I think I'm gonna try and find a replacement cap. See if RFparts has something if my junk box doesn't pan out.
Well I bent front and rear plate out so it wasn't so close. Brushed off with a fine paint brush and a light clean. Afterwards, I noticed coil was touching side of case and I could see a tiny spark. Luckily I have a roll of 5/16" teflon tubing. Cut a short piece and cut a slit in it. Wrapped it around copper and used a few wire ties to secure. Its doing about 400w pep with around 12-14w pep drive. Looks like I got it fixed. Thanks for everyones suggestions.
73's
73's
One more suggestion, if you're using it on SSB, make sure your ALC in your radio is intact, and not cranked up all the way. This will keep your average power in check. Also, if on AM, keep the carrier level reasonable, (read: low) and don't overmodulate. The reason I mention this is sweep tubes are delicate if abused, however, if ran properly and conservatively, they can last quite a long time. In a lot of these amplifiers they were ran at really high plate voltages in order to get the output power they produce with little regard to how long the tubes would last. Also, the PI network (load and tube network) in the amplifiers weren't designed all that well to match the impedance of the tubes so what isn't going out the antenna jack is wasted as heat.
My point is, run the amplifier and enjoy it, but we don't want to see you having to buy tubes for that thing in six months or a year. They are scarce now and expensive compared to when it was built.
My point is, run the amplifier and enjoy it, but we don't want to see you having to buy tubes for that thing in six months or a year. They are scarce now and expensive compared to when it was built.
I repaired it for a friend. But I agree. I hope he runs it lightly. He also dropped off a dentron 160-10L. Needs a lot more work than this.