Y278

[wa3dsp]

I wonder if anyone has ever built an amplifier using the Y278 water cooled version of the 4CX250B? This looks like it would be a nice quiet version and the available computer coolers would probably work.

[W1ITT]

The 4CX250 series was designed for Class C operation and doesn't show good IMD number for linear operation.  But they work.   Water can move a lot of heat.  My friend Joe, K1RQG (sk) used to run a ring of six 7289s on 1296 for moonbounce.  The water jackets were connected in series and he used an aquarium pump to circulate the water into a 5 gallon container and back, with no fancy heat exchangers.  Those radiator things that the computer overclockers use might be OK and make for a compact unit.
Many of the biggest short wave transmitters use water or vapor phase cooling.
73 de Norm W1ITT

[w8khk]

snip.........Many of the biggest short wave transmitters use water or vapor phase cooling.
73 de Norm W1ITT

There was once a "moderately sized" MF broadcast transmitter in Ohio that employed vapor-phase cooling.  It worked very well but was taken out of service for other reasons. Could it have had something to do with the neighbors up north?  Now it is PW, compared to previous performance.

[KD6VXI]

The 250 can show decent imd numbers, but it will never equal the 88 series of tubes.  Or the 3000.

But if you build a STIFF screen and grid supply it will run in the mid 30s, pretty much where everything else is nowadays.

But with the yoyo screen supplies some people make it's no wonder the 250 has such a bad history.

Wouldn't be my first choice for a new build, but I've built tons of them over the years.

--Shane
WP2ASS / ex KD6VXI

[Detroit47]

Hey Shane

Think Teiestar, Minuteman, John Boy, Golden Falcon..............


47

[wa3dsp]

My first experience with the 4CX250 was in the Air Force back in 1970. The Collins 618T amplifier used two and was on the KC135's and some B52's.

[Tom WA3KLR]

From the old ARRL "Single Sideband for the Radio Amateur" book - the table in the back on tubes in grounded cathode circuit, page 252:
4CX250B 295 Watts out with 2000 Vdc
4CX250R/7580W 470 Watts out with 2000 Vdc. surprising to me.
  screen voltage is higher, max. plate current is higher, but doesn't add up.

https://tubedata.wernull.com/sheets/140/7/7580W.pdf

Looking at the Eimac data sheet, confirms 470 Watts out. This version tube was specifically designed for AB1 linear operation. Most pentodes and tetrodes had the (non)linearity as the limiting factor rather than the plate dissipation. Tubes designed for linear service usually had the linearity and plate dissipation matched well.

[wa3dsp]

It is amazing the number of tubes Eimac made.

https://frank.pocnet.net/other/Eimac/Eimac_QuickReferenceCatalog_1963.pdf

It looks like the Y-278 is equiv. to the Eimac 4W300B

[KD6VXI]

Hey Shane

Think Teiestar, Minuteman, John Boy, Golden Falcon..............


47

Those where exactly the ones I was thinking of.

My favorites where the ones that ran 2.2kv on the plate with 6 capacitors in series.

The screen supply came at the tap of the first and second capacitor from ground.

Screen voltage was a yoyo.   Literally was moving in direct response to plate current.

And boy, they took up a TON of spectrum.


--Shane
WP2ASS / ex KD6VXI