[Amps] 4 KW?

[Alek Petkovic]

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 jim.thom at telus.net wrote:
> Date: Fri, 24 Jun 2022 06:14:27 -0500
> From: Rob Atkinson <ranchorobbo at gmail.com>
> To: "amps at contesting.com" <amps at contesting.com>
> 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.
>
> <Rob
> <K5UJ
>
> 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.
>
> https://www.eham.net/reviews/view-product?id=12132
>
> Jim  VE7RF
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