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Re: [Amps] 4 KW?

Subject: Re: [Amps] 4 KW?
From: Alek Petkovic <>
Date: Sat, 25 Jun 2022 08:49:40 +0800
List-post: <>
Well, you can add a second bad review.

The last review on Eham, for the FU718F tube, is from VK6WB. It is his Emtron DX-2SP that my friend bought in which the tube lasted a month. We then bought the spare tube that VK6WB reviewed and it lasted less than a month before it flashed over.

I have a couple of 4CX1500B tubes so we put one of those in and got the amp going again, albeit on lower power, because the low screen volts in the amp are not suited to that tube.

Then we bought two used 4CX1000A tubes from VK2ABN and our troubles are over. They each make full power and my friend is happy. The tubes are 1985 date codes and they have been around. I believe they will keep going around for many more trouble free years and the tubes will be rotated through the amp to keep them fresh.

The FU728F will fit into a 4CX1000A socket but not vise versa, because of the thicker key rod in the centre of the FU728F socket. The FU728F tube has a matching larger hole in the base.

When Rudi built his amps, he had the centre pin in the socket machined down to fit the Eimac tube and he added the 6 volt tap on the transformer for the heater. The Chinese tube runs 9 volts.

This move has virtually future proofed his amplifiers. Yes the Eimac 4CX1000A tubes are very expensive but at least you can get them and they are reliable.

73, Alek, VK6APK

On 25/06/2022 2:18 am, jim.thom wrote:
Date: Fri, 24 Jun 2022 06:14:27 -0500
From: Rob Atkinson <>
To: "" <>
Subject: Re: [Amps] 4 KW?

<Never heard of the FU728F.  My concern would be that it vanishes like
<the 4CX1600.  Interesting about the failures.  I guess the type number
<is telling.  Say "FU" out loud.


It's a chinese version of a 4CX-1500B..on steroids.  It's a popular tube
that was used in Emtron amplifiers...and is currently being used in
OM-Power amplifiers.

1 Bad review on e-ham.

Jim  VE7RF
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