What is meant by 'Extended Cut-off'?

[Alastair E]

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]

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]

Well, I guess thats why they were cheap!

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

 

[Alastair E]

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?

 

[EC8010]

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]

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.