You had a weak 1500B.? Its a far better tube and for sure will make more power.? I have swapped these many times.

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C

From: [email protected] <[email protected]> on behalf of Alek Petkovic via groups.io <vk6apk@...>
Sent: Sunday, November 26, 2023 4:26 PM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] CX1500

Rudi was clever. He had the socket centre pin modified to take the Eimac tubes and put a 6V tap on the transformer in the DX-2SP amplifier. I have tried both the 4CX1500B and the 4CX1000A in a friend's amp and the 4CX1000A is the much better choice. The output with the 4CX1500B installed was quite a bit lower.

73, Alek VK6APK

If an amp uses FU728 by design and has an actual 728 socket stem, a 4cx1000 will not just fit in. The center shaft is too wide in diameter. ?It may be possible to enlarge the center hole on the 4cx1000 with the right size drill bit to make it fit. ?The FU728 with a larger hole will fit a real 4cx1000 socket without an issue. ?Change filament voltage of course either way..

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On Sunday, November 26, 2023, 6:49 AM, Adrian Fewster <vk4tux@...> wrote:

Alek, see?

Can dropin for a FU-728 with filament voltage changed to 6v ..

73

vk4tux