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Old 24th February 2009, 10:54 PM   #11
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Old 24th February 2009, 11:03 PM   #12
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Old 25th February 2009, 01:09 AM   #13
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What exactly is a sweep tube?
Sweep tubes were used to power the deflection yoke mounted on the CRT's neck. A good deal of "sock" is needed to move the electron beam(s) across the phosphor face, especially at the large deflection angles that became popular. A large deflection angle allows for a shorter CRT and a cabinet that is reasonably "shallow".

2X tubes, of the same type, are needed to build a SE stereo amp.

If the mu of a triode wired 6JC6 is 40 or greater, it will serve nicely as the voltage gain device in a "flea power" SET amp. Perhaps George (Tubelab) can tell us what the mu is.
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Old 25th February 2009, 01:28 AM   #14
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The 3 "sweep" tubes. What exactly is a sweep tube?
"Sweep" tubes were originally designed to "sweep" the electron beam back and forth across the face of a TV picture tube to paint the picture. It is also responsible for generating the high voltage needed to operate the picture tube using a step up transformer known as a flyback. Early sweep tubes were made out of audio tubes. One of the first was the 6BG6 which was nothing more than a 6L6GB with the plate wired to a cap on the top of the tube to better deal with the high voltages.

As TV sets got bigger, more power was needed to sweep the beam across a larger screen, and more power was needed to generate the higher voltages to light up the bigger screen. When color TV came out even more power was needed. The poor sweep tube operates at full power all of the time. "Turning down the volume" on the sweep will make the picture smaller.

The sweep tube evolved into a purpose designed power tube able to run at full power for hours at a time 7 days a week. The 3 type numbers that you have are from the end of the vacuum tube TV era and are some hefty tubes.

During the CB radio craze of the late 1970's people figured out how to make some big booster amplifiers (highly illegal) using as many as 10 of these tubes wired together. These amplifiers ran the tubes far above the published ratings leading to short tube life. This alone has resulted in stratospheric prices and limited supply of some sweep tubes.

Several audio engineers, experimenters and commercial manufacturers (including McIntosh) figured out that sweep tubes could be used to make some serious audio amplifiers. Most sweep tubes can be used to make push pull amplifiers and power levels of 50 to 150 watts can be often extracted from a pair of sweep tubes. Some sweep tubes will work in a single ended amp, and some will not. Unfortunately the only way to find out is to actually hook them up and test. I am not aware of any published schematics for these 3 tubes in SE mode, but they may be out there. The McIntosh MC-3500 used 8 6LQ6 tubes to crank out a very conservative 350 watts.

There are several users on this forum (including me) that have been experimenting with sweep tubes. Some of these experiments can be found in these this thread:

Tube sale at AES

More sweep tube experiments are planned when I have the time, but I tend to play with tubes at the other end of the price spectrum. Some sweep tubes never gained popularity with the linear amplifier crowd, and were either not popular in the TV world (supply exceeded the demand), or extremely popular (millions made). These can be found in the tube sellers bargain sales for very low prices (sometimes $1 each). I have a few used tubes of the types you have, but I may never experiment with them due to their high prices.
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Old 25th February 2009, 01:34 AM   #15
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Perhaps George (Tubelab) can tell us what the mu is.
Don't know yet, but there are 4 of them sitting here in a large box full of tubes that will get evaluated as driver tubes. I have a rather large list of tubes to test, so I can't say when these will get done.
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