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parafeed headphone amplifier

The 6J6 Tube and its variants

Tubes, otherwise known as vacuum tubes or electron tubes, form the basis of the TORPEDO! Along with the transformers, the tubes produce the audio characteristics of a true, high-voltage, output-transformer-coupled headphone amplifiers. Many books have been written about tubes and their sound quality. An excellent article on "How Tubes Work", their parts and operation is online at Dale and Roy's
Rather than focus on complicated tube theory, however, some basic info on the specific TORPEDO! tubes (we'll take the liberty of calling them "TORPEDO! tubes") may be more helpful. Besides giving the TORPEDO! its genuine sound due to the tubes and transformers, the other interesting aspect of the TORPEDO tubes is that they are extremely cheap and more importantly, particularly to you Starving Student fans who saw the 19J6 disappear - they are plentiful. This allowed Dsavitsk to come up with the unique PCB design of the TORPEDO parafeed headphone amplifier.
The 6J6 tube is a dual-triode tube rated for 300V on the plates. For the TORPEDO! parafeed headphone amplifier, the triodes in each tube are paralleled, with the power transformer voltage providing the plate voltage at 200V, about twice the normal operating recommendation. The result is a high-voltage tube circuit that is more or less self-balancing for the tube pairs.

The 6J6 has the following basic attributes when run at 100V on the plates:
  • Basic amplification factor of 38,
  • Transconductance of 5300 micromhos, and
  • Plate resistance of 7100 ohms.
  • The 6J6 tube was part of a series of tubes of the same design, but different heater voltages: 6J6-5J6-19J6 (6V, 5V, and 19V heater voltages, respectively). Unlike the 19J6 or 5J6 tube, however, numerous manufacturers produced the 6J6 tube in great numbers. Here are data sheets from three different mfrs of the 6J6 tube family (pdf files):
    6J6 (GE) 6J6 (TungSol) 6J6 (RCA)

    Other Tubes for the TORPEDO!
    There are many other tubes that can be used with the TORPEDO! TDSL (Tube Data Sheet Locator) indicates the following tubes are equivalents: Among the full equivalents for the 6J6 tube are many variants of the 6J6 itself: 6J6-A, 6J6S, 6J6-W, and 6J6-WA.

    Further, near-equivalents for the 6J6 are numerous:
    1216, 5844, 5964, 6030, 6045, 6099, 6101, 6535, 6927, 6CC31, 6MNN3, CK6101, CV5046, CV8160, CV8231, ECC91, M8081, and T2M05. If one drills down deeper at TDSL by starting with the full equivalent variants such as the 6J6-A, 6J6-W, etc., you can find even more. Beezar and ECP Audio have done extensive testing with the 5844 and 5964 and found them to run fine in the TORPEDO!. Those tubes and the data sheets we've been able to collect are here:
    6J6-A (RCA)
    6J6-A (TungSol)
    6J6-WA (TungSol)
    5844 (Sylvania) 5964 (TungSol)
    5964 (Sylvania)
    6101 (RCA) ECC91 (Mullard)
    ECC91 (Philips)
    ECC91 (RFT)
    M8081 (Mullard)

    Generally speaking, TORPEDO! tubes and their sound is distinguished primarily by tube type, but sometimes by construction. By construction, we specifically mean the getter and its placement. While the getter style probably has nothing whatsoever to do with the sound quality (most likely the plates do that), it is still a pretty good visual indicator of different overall construction of the tubes, period.

    The tube getter, accompanied by the silver "splotch," is a loop of wire. The loop creates a localized charge field that when catalized by the chemical in the silver splotch, burns up excess gas molecules that may have leaked inside of the tube. In the TORPEDO! tubes, these getters can be circular, square, or horseshoe shaped (sometimes called a "D" getter) and can be located on the top of the tube or over to the side of the tube top. The photos at top of this web page are two tubes with different getters - one has a top horseshoe getter, the other - a top halo getter. Here are a couple of photos that show another getter type:

    The tube above has a top-square getter. The getters need a bit of time to burn off the gas molecules that have infiltrated the tubes while sitting unused for the last several decades. That said, at 200V it really doesn't take too long. Unlike some of the low-voltage tube hybrids, whatever's in the tubes in the TORPEDO! gets burned off pretty fast!

    Selecting and Buying TORPEDO! Tubes -
    In selecting/buying TORPEDO! tubes, one thing to remember is that variation exists in NOS tubes. They are not like opamps, transistors or other semiconductors. With few exceptions, silicon-based active devices are consistent to a certain level of performance. While tubes were similarly rated, even new - they were nowhere near as consistent in their performance. The sound of your TORPEDO! can depends greatly on the tubes. While the transformers also have a great effect, they can't be rolled in and out of the amp.

    What does this mean to the TORPEDO! builder and owner? Quite simply, buy more tubes and try more tubes! You may be delighted to find how different they can be. (As cheap as they are, there's no excuse.) The differences range from slight to great, but can be inconsistent. Ordinarily, one might recommend a certain brand for a type of sound, but you may find a particular tube construction stamped/marked by any of the manufacturers.

    This tube was unfortunately destroyed when the tip was accidentally broken off. However, it is an educational photo from the perspective of the getter "flash." Instead of a chrome silver, the getter has completely oxidized and turned white, indicating a total lack of vacuum in the tube. As you might guess, the tube is irreparably damaged. It's nice to know what to look for if your tubes go bad, though - without an accident.

    Finally, there's an interesting accessory you might be interested in if you start buying/collecting many tubes. A tube pin straightener:

    These can be picked up for a few dollars on e-bay.

    file last changed:Saturday, October 17, 2015 6:55:47 PM
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