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Author Topic: 3cx800 pulls...anybody have them?  (Read 1873 times)
K3JVB
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« on: February 27, 2010, 08:47:41 AM »

Hi all

I am looking for a spare 3cx800a7( 3cxp8007a7). I know that they have not been used for Mri's in a few years. But was wondering if anybody sells "pulls" any longer.
They seem to be getting scarce, and would like a spare.
thanks
John
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K6AER
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« Reply #1 on: February 27, 2010, 09:03:44 AM »

The 3CX800A7 and 3CPX800A7 are still being made by several manufactures. MRI folks stopped using those tubes 10 years ago. Pulls are mostly stock rolling around in someone’s drawer.

Expect to pay about $700-$800 for a new tube. There are Chinese tubes available but always buy for a supplier who provide a warranty. Richardson is very good about warranties.  A good tube will require no more than 20 mA grid current for 800 watts out.

The 3CPX800A7 will put out more intermittent power if the power supply is capable but if the amplifier voltage is designed around the 3CX800A7 no more power will be had by installing the pulse version. Both tubes have 800 watts CW dissipation. The CPX version has more anode spacing for higher voltage.

The good news is that even a NOS tube will work just fine. I bought a pair of NOS Eimac’s from 1995 and installed them into an Alpha 86. At 1500 watts out CW the grid current was about 25 mills. I generally start looking for replacement tubes when the grid current goes over 50 mA for 1500 watts out.

My last set of 3CX800A7’s are in an amplifier that is still being used after 24 years. Don’t overdrive them and they will last a very long time. Notice I said drive…The grids are what fails on the tubes not the anode.

Check QTH.com for tubes.
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