sweep tubes and audio application?

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
http://s1354.photobucket.com/user/myrtlebeachsound/embed/slideshow/6JM6_Audio_Amplifier
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.

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.

Thanks!

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

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 thank u all...

The Berning 2100 and the Counterpoint SA4 both used the now ridiculously expensive 6LF6 (though it is a very nice output tube). Expect $80-$100 per tube for NOS; you have ham operators to thank for the price.

-Richard

Milbert and Berning amps use the 6JN6 tube. NOS are still $4-5 each, often a buck a piece at ham shows. After many years of use, I've never had one go bad.

John C.

Mcintosh Mc-3500 & mi-350 use the 6lq6 6mj6 sweep tube. Kirkus is correct about the transformer winding ratio's as the Mc-3500's have three separate transformers one of them being a very complicated winding configuration with only one company capable of winding this transformer.

Also 6lq6 tubes are costing around 40.00 a pop and you will need 16 for a pair of these 350 watt amps.

On the positive side these amps are one of the best sounding amps ever and will take on any S/S amp with comparable output

"Sweep tubes" refers to types of tubes that were designed for the horizontal-output circuit of tube-type TVs. They generally have reasonable current ratings, high voltage ratings, good gain, and used to be cheap and widely available. The classic DIY amplifier application was not for audio, but for amateur radio as a linear RF amplifier.

On the downside, they're desinged for high-impedance place circuits, so an output transformer to utilize them in a traditional audio amp would have to have a very high turns ratio, which would compromise performance. Now for a very high-impedance application they can work well, such as the Acoustat direct-coupled electrostatic-speaker amplifiers, which indeed used sweep tubes.

But there's also the reason that since it's been what, 35 years since tube TVs were common? So they're not nearly as cheap and plentiful as they used to be, meaning that there's no longer much of a reason to find uses for them so tangential to their original application.