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CX1500

 

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..


Sent from the all new AOL app for iOS

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

 

开云体育

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

On 26/11/2023 8:00 pm, Louis Parascondola via groups.io wrote:

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..


Sent from the all new AOL app for iOS

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

 

开云体育

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

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

On 26/11/2023 8:00 pm, Louis Parascondola via groups.io wrote:
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..


Sent from the all new AOL app for iOS

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

 

开云体育

If you run a drill bit into the base of a 4x1k or 4x1.5k to enlarge the hole slightly, you'll also wind up grinding out that dimpled keyway that aligns the tube with the notched socket shaft. Of course, for a tube that's otherwise unusable, that's mostly-inconsequential.

Steve, K0XP


On 11/26/2023 4:00 AM, Louis Parascondola via groups.io wrote:
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..


Sent from the all new AOL app for iOS

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
--
See my QRZ.com page at

 

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OK. That's very encouraging. You could be right, as we had no other 1500B tubes to compare it with.

Thanks, Alek.


On 28/11/2023 1:24 am, W7WRX wrote:

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

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

On 26/11/2023 8:00 pm, Louis Parascondola via groups.io wrote:
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..


Sent from the all new AOL app for iOS

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

 

开云体育

Hi guys. I found this on another site – interesting !

?

Regards,

?

John VK6JX

?

?

?

From: [email protected] <[email protected]> On Behalf Of W7WRX
Sent: Tuesday, November 28, 2023 1:24 AM
To: [email protected]
Subject: Re: [ham-amplifiers] CX1500

?

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

?

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

On 26/11/2023 8:00 pm, Louis Parascondola via groups.io wrote:

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..

?

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

 

开云体育

I have a 4cx1500B with 350 screen, 3500 volts plate. It does 3kw peak on SSB.? Its been run at 1500 with 2500 volts on plate for 4 years now.? Very important to have a negative and positive going screen meter so you can tune it properly.

The 4cx1500A is a completely different tube. Its directly heated, Has a huge Filament current of 40 amps, Tons of emission and is flat out a beast of a tube.? Probably one of the most over looked.?

There is also a 5CX1500A that is pretty much the same as the 4cx1500 but has a suppressor grid that gets grounded.? Those tubes where used in industrial generators and are fairly cheap.? A friend built an amp with this tube and it is incredibly clean. He has IMD down very low.

I have 6 of them with several sockets.? I plan to build a dual 5cx1500 amp for HF in the next year or so.? The cabinet, Roller and other parts are all in the garage.?

C

From: [email protected] <[email protected]> on behalf of John Sparkes via groups.io <vk6jx@...>
Sent: Tuesday, November 28, 2023 1:19 AM
To: [email protected] <[email protected]>
Cc: vk6jx@... <vk6jx@...>
Subject: Re: [ham-amplifiers] CX1500
?

Hi guys. I found this on another site – interesting !

?

Regards,

?

John VK6JX

?

?

?

From: [email protected] <[email protected]> On Behalf Of W7WRX
Sent: Tuesday, November 28, 2023 1:24 AM
To: [email protected]
Subject: Re: [ham-amplifiers] CX1500

?

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

?

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

On 26/11/2023 8:00 pm, Louis Parascondola via groups.io wrote:

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..

?

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

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