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Title: Swapping 4-250 for 4-400 tubes Post by: kc2wts on November 14, 2017, 08:53:47 PM Hello, I have a homebrew transmitter with a pair of 4-250s in it modded by 810,s . I crapped out a 4-250 the other day-filament, and was just going to replace with 4-400,s Anybody ever do this? Thanks, John
Title: Re: Swapping 4-250 for 4-400 tubes Post by: WD5JKO on November 15, 2017, 06:54:03 AM Before you switch, make sure the dark tube is really bad. The filament pins can get quite hot, and one or both pins may have gotten hot enough to melt the solder leading to a bad connection. As far as switching to 4-400's, sure why not. My experience is limited, but with a Globe King 500, the 4-250 seemed to be more efficient. That said, my 4-400's were broadcast pulls gotten from W1GAC. Those could have just been tired tubes. Jim Wd5JKO Title: Re: Swapping 4-250 for 4-400 tubes Post by: Bob W8LXJ on November 15, 2017, 08:48:50 AM My KW-1 had an intermittent 4-250 and I replaced them with good 4-400A
tubes. Direct swap, no circuit or voltage changes. Been running it that way for 20 years with the same set of tubes, no issues. Do check the solder on the 4-250 filament pins. Had a friend who have that problem a a Johnson 500. He put a small blower at the tube socket under the chassis to cool the pins. Worked. Bob Ohio Title: Re: Swapping 4-250 for 4-400 tubes Post by: WD8KDG on November 15, 2017, 01:30:01 PM John, AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
The swap should be a plug & play. Although when I've replaced large TX tube, always checked the neutralization afterwards. Trivia......Junkston "500's" left the factory with a fan under the chassis/tube socket for the 4-400A. Just the same, check the pins & solder. Craig, PS: I've never worked where 4-400A pulled tubes were available. 4-250A's (new in box) have been found at fests for about $10-$20 US dollarettes. |