What is meant by 'Extended Cut-off'?

Alastair E · 5th May 2005, 11:03 AM

Im using some Nuvistors in a project which normally uses 6CW4 valves, But Ive managed to get some nice NIB 6DS4, alleged to be an equivalent.

According to the RCA/Philips data, the valve is called an 'Extended Cut-Off' tube'

What does this really mean?--They are to form the triodes in a Mu stage, are there any operating points I should avoid?

Thanks!

EC8010 · 5th May 2005, 11:05 AM

Sounds like a variable-mu valve to me, and therefore bad news for low-distortion audio. Another name for variable-mu is "remote cut-off".

Alastair E · 5th May 2005, 11:12 AM

Anyone got a nice cct diagram for a valve attenuator!!

Alastair E · 5th May 2005, 12:40 PM

Most places list the 6DS4, as a Hi Mu tube, its only philips sheet, I think that list it as 'extended cut-off'

Any comments anyone?

EC8010 · 5th May 2005, 01:59 PM

I've just looked it up and RCA list it as "extended cut-off". I looked at the curves, and it's a variable-mu type. Sorry.

Brian Beck · 5th May 2005, 02:18 PM

EC8010 is right. While the non-variable mu tubes are better, you may not want to throw the variable ones away just yet. They can be made to play acceptably in differential stages or in other balanced stages where the even-order distortion which is generated by the variable mu is largely cancelled out. Even then the non-variables are preferred but just not by so wide a margin.

5th May 2005, 11:03 AM	#1
Alastair E diyAudio Member Join Date: Feb 2004 Location: South Wales	What is meant by 'Extended Cut-off'? Im using some Nuvistors in a project which normally uses 6CW4 valves, But Ive managed to get some nice NIB 6DS4, alleged to be an equivalent. According to the RCA/Philips data, the valve is called an 'Extended Cut-Off' tube' What does this really mean?--They are to form the triodes in a Mu stage, are there any operating points I should avoid? Thanks! __________________ Das Beste Oder Nichts

5th May 2005, 11:05 AM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Sounds like a variable-mu valve to me, and therefore bad news for low-distortion audio. Another name for variable-mu is "remote cut-off". __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

5th May 2005, 11:12 AM	#3
Alastair E diyAudio Member Join Date: Feb 2004 Location: South Wales	Well, I guess thats why they were cheap! Anyone got a nice cct diagram for a valve attenuator!! __________________ Das Beste Oder Nichts

5th May 2005, 12:40 PM	#4
Alastair E diyAudio Member Join Date: Feb 2004 Location: South Wales	6DS4 Most places list the 6DS4, as a Hi Mu tube, its only philips sheet, I think that list it as 'extended cut-off' Any comments anyone? __________________ Das Beste Oder Nichts

5th May 2005, 01:59 PM	#5
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	I've just looked it up and RCA list it as "extended cut-off". I looked at the curves, and it's a variable-mu type. Sorry. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

5th May 2005, 02:18 PM	#6
Brian Beck diyAudio Member Join Date: Dec 2004 Location: South Florida, USA	EC8010 is right. While the non-variable mu tubes are better, you may not want to throw the variable ones away just yet. They can be made to play acceptably in differential stages or in other balanced stages where the even-order distortion which is generated by the variable mu is largely cancelled out. Even then the non-variables are preferred but just not by so wide a margin. __________________ Brian

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