Dentron 2500B Question

[BJ radionut]

Good morning everyone,
I know this post is several years stagnant, but I just picked up a 2500B yesterday and have lots of questions. for starters, when I opened it up I have realized that it does not have the transmit tube installed.. Upon further reading, it is apparently supposed to have 2 tubes, but this seems to only have 1 socket... is there anyone familiar with these enough to help me determine what I actually have and if it's worth investing time or should I just sell it.. the best way to reach me is via email KG4WWH at gmail....

Thanks a bunch in advance!!

Adam
KG4WWH

Most likely converted to single 3cx800 EIMAC... Original tubes were 8875 (on the never to be found list) See top of thread, many were converted to "Rusky" tubes...Due to cost of replacement...Might show pictures of amp / socket Top and Bottom could give us a clue what someone has done to mortify it.

https://www.cpii.com/docs/datasheets/174/3CX800A7.pdf

Tubes and RF Components for sale

USED Medical usage PULLS can be $350-$500 ...EACH
NIB (when available) $1500-$2000 EACH for USA MADE

https://www.dxengineering.com/parts/plb-3cx800a7

CHINA MADE

 

[nomadradio]

Urban legend. I have copies of Eimac's promotion ad for that type tube. The exact same innards are used in three types, 8873, 8874 and 8875. I'll skip the boring part about "radial beam triodes". All three have the same innards with three different structures to remove the anode heat. The 8873 has a solid copper ring with a flat spot. It's meant to be bolted to a heat sink with a chunk of beryllia ceramic to insulate the high voltage on the anode surface from the grounded heat sink, and carry the heat flow. They rate it at 250 Watts.

The 8874 has radial fins inside a metal ring like the 4CX250B tube, but bigger. This one is the "3CX400" version. Anode rating is 400 Watts.

The 8875 has horizontal fins inside a wide "sombrero"-looking ring with a large hole on opposite sides. The widely-space fins can be used with a simple fan, rather than the blower needed for the radial-fin tubes. The wider spacing of the fins reduces back pressure enough you can just blow air across it with a fan. Eimac rates this version at 300 Watts dissipation.

Each of these is a proper transmitting tube. Fully capable of putting out enough power to destroy itself, if you ask it to.

I'll make an effort to track down that magazine ad.

Oh, and a MLA2500 with only a single tube socket has been modified. Guarantee.

73

 

[KG4WWH]

Here are some pics of the amp. Hopefully they upload...

 

[357]

It was pin 5 to ground that the solder cracked if anyone is curious. hard to see

 

[Radio Tech]

man I used to hate seeing anything with the name Dentron come in.
Those things will eat a set of tubes for a snack. Seen so many that were chopped up and mono banders made out of them, and I want even get into the Amp Supply stuff.

However not to hyjack the thread but since we are talking unotainable tubes I need to find a 8874 replacement.
Picked up a nice Henry Tempo 6N2, less the tubes.

 

[nomadradio]

Suicidal setup, looks like. Don't know who told you it would take a "three-see-ecks eight hundred" tube but that's the wrong socket. The "3" tube uses the exact, same original 11-pin socket that the factory tubes used. Your socket has 7 pins.

Any tube with a metal ring surrounding cooling fins will usually not work with an axial fan like the one in the picture. The close spacing between cooling fins creates back pressure. As a rule, more back pressure than a blade fan can push against. This is why you find centrifugal blowers in a commercial amp using that kind of tube. They will push against back pressure that a blade fan can't.

Just gotta have air across cooling fins.

So, uhh.. Where's the tube?

73