8935 tube - good for anything?

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Bill, KD0HG:
Now that I think of it, the 3CX2500 series is also easy to find.

In spite of the tube number, they've got ~4 KW of plate dissipation. The 2500A7 and 2500H3 has leads and doesn't need a socket. The 2500A3 has no attached leads, but it's easy enough to attach connections to the base with hose clamps. It's filament voltage is a common 7.5 volts (at 50 amps).

This jug was used in the Collins 21E and Harris MW-5.

Many years ago I build a grounded grid linear amp using one. Power gain in that mode was around 6. I floated the filament transformer and put the RF chokes in the primary so only around 3 amps needed to be handled by it.

Grounded cathode AB2 the thing would do 6 KW out with 150 watts of drive.

IIRC, there was also a 3CX2500 variant specifically designed for low-IMD linear service (I don't remember the suffix), but they're gonna be scarce if you can find one. The A3s, F3s, and H3s are all currently made by CPI-Eimac, in China and by Svetlana.

K1JJ:
Quote from: Bill, KD0HG on January 26, 2009, 09:20:26 PM

Now that I think of it, the 3CX2500 series is also easy to find.

Grounded cathode AB2 the thing would do 6 KW out with 150 watts of drive.


How 'bout that... I did the same thing, Bill.

Back in the mid 70's I first tried one in GG linear and found I needed a 4X1 to drive it... :-)

So then went to grid driven linear config and even neutralized it. (It sure needed it) That worked better, as you found, but wasn't too clean.  I worked at it and found it cleaned up somewhat when I ran it in full A1 dissipation...  :-)  Gawd what a power hog.  So went on to something else.

It sure is a common tube.  For AM, I'll bet running it in class C, neutralized, grid modulated would  be just fine. 

Of course, the old standby, one modulated by a pair is the obvious choice of the commercial guys.

Hope to catch ya on, maybe this weekend, OM.

T

Bill, KD0HG:
Looking forward to it.

Most likely I'll be out of the Ghetto around 3700, + or -. I've got my antenna lowered some 50 feet because of recent winds, I'll hoist it by this weekend.

That linear with the 3CX2500 was the first one I ever built. Yer right, definitely a drive-hungry beast. I could have best used something like a 30L-1 to drive it. It did make enough juice to melt my RG-8 feedline one wet night, the shorted output caused it to blow the 30A breakers in my parents' house...The current surge made the metal conduit *BANG* like it was hit by a hammer..My dad almost ended my budding ham career right then and there. That, on top of my locking the thing key down and running around the front yard waving a lit four-foot fluorescent bulb like a star wars light saber..

b

Opcom:
Well let's see how much the old boatanchor is going to cost. Better than having it rot forlorn in the warehouse. Yall have fun with yer radios! I hope to have a real antenna in a frew months. Tree service comes Tuesday.

K1JJ:
Quote from: Bill, KD0HG on January 26, 2009, 10:24:55 PM

It did make enough juice to melt my RG-8 feedline one wet night, the shorted output caused it to blow the 30A breakers in my parents' house...The current surge made the metal conduit *BANG* like it was hit by a hammer..My dad almost ended my budding ham career right then and there. b


heheheh -  Yep the parents just didn't understand it was part of the shakedown... not necessarrily a bad or permanant thang.

With that same 3cx-2500, I too, had a short circuit, but in the amplifier.  I had used #6 wire run around the cellar to the mains. I didn't use a fuse or breaker cuz I didn't have one.  That #6 wire melted and smoked so bad it filled the cellar with a gagging black smoke before I cud turn it off.  It happened so fast. I opened the hatchway, but it was too late - the OM smelled it thru the floor and came down stairs and freaked out... :-)   

He didn't shut me down, just yelled. I guess he understood since he helped me from the Novice days. In fact, he took Ed Hare (W1RFI) and me up to Boston for our General tests in June, 1966, so he knew a little about the insanity.  I had failed the Conditional test a month before (bummer) but we both passed the General this time.


Patrick: Well, you've sure got some good parts to work with until that antenna goes up... :-)

T

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