sweep tubes and audio application?

I am asking the members of the Gon what plus and minus are there with using sweep tubes {TV Tubes} in the designing of amps and preamps in audio today. I have been told they are cheaper tv tubes and last longer. I like to know if they are best at sound reproduction or just smoke and mirrors? And are their any members using them with success.I thank you all for answers to my questions
The 6LF6 was used by Futterman in some of his OTLs. They have high-current low-voltage capability. They have become rather expensive as they are no longer made.

These days the EL509 is the tube that replaces the 6LF6 although not directly. It is a powerful sweep tube and is also used in OTLs. There is a non-plate cap variant that could be used, but FWIW the KT90 was developed from this tube, so if you really want something like that the KT90 is probably the place to look, as the design of the amp is made simpler by having no plate caps and the use of octal sockets.

I appreciate the clear and concise explanations. Just the info I was looking for, no more no less.

I've come to despise ham radio explanations on certain information. They are almost always too wordy, and poorly written. Often, in their attempts to appear intelligent and articulate, they achieve neither.

Thanks again
My Acoustat servo amps for my AcoustatX speakers use 4 6HB5 tubes per amp, and it's also an OTL.
Made in the mid 1970's ,they have stood the test of time.

So using TV tubes isn't something new.
I have Dennis Had ( former owner Cary Audio) Inspire audio amplifier he built me a few years back. Features 6JM6 Compactron tubes. Picture at link
love this little amp and actually prefer the sound over my other Dennis Had Inspire amp using EL-84 tubes,
A bit unnerving buying a new amplifier that uses tubes that are no longer made but the whole demand supply thing is in my favor. I don't guess a lot of people have TV's around still using these tubes so as of now easy to find and cheep. Just this week I won a few NOS 6JM6 tubes for UNDER 3.00 a tube so I can by enough stock to outlast my amp.
I love the look of the wire connected to the top of the tube and I love the sound. I was told I should get 10 years out of a set of tubes.