JAN G.E. 6V6GTY Replacement for JJ 6V6S

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Brent Hutto, Apr 6, 2008.

  1. Brent Hutto

    Brent Hutto Member

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    The 6V6 that came with my Richter RS 5.8 amp was a JJ 6V6S. It sounds good, as does the JJ 12AX7 that also comes with. For that matter so does the NOS Sylvania 6L6GC she also sent but I like the 6V6 sound better. A nyway, being the curious creature that I am I had to try a JAN G.E. 6V6GTY brown-base (dated 1972) that I had used in my little Champion 600.

    Here's my question. Would you expect the overall gain to be similar between the JJ 6V6S and this old 6V6GTY? I have no way to measure but I would be willing to swear in court that with the 'GTY the amp played several decibels louder with the same volume setting as it did with the JJ. Not only that but the hum and light-fixture noises from my single-coil Strat sound a little more prominent as well. Maybe it's not that odd that type of 6V6-family tubes vary in gain but this seems like 4, 5 maybe even 6dB to my uncalibrated ear.

    Unfortunately, I think the tube is a bit prone to mechanical noise as well. At very modest volumes I get a buzzy metallic sound that wasn't there with the JJ or the 6L6. Of course it's a combo but I can't say for sure that the noise comes through the speaker. It sounds to me more like it's coming from the back of the amp, maybe even from a tube. It happens when I play either a low A or Bb.

    One other thing. How much less voltage/current/dissipation can these old brown-base 70's tubes handle than the rather overbuilt JJ 6V6S? According to the builder, as shipped with the JJ it runs [FONT=arial,sans-serif]380V plate and is biased with a 680ohm resistor producing 25V. That's about 37mA or maybe 14-15W dissipation by my reckoning. And I'm likely to fry an old 6V6GTY with that?
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  2. Blue Strat

    Blue Strat Member

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    Interesting questions! I've not seen a spec sheet for the JJ, but it's said to handle much higher plate voltages than other (real?) 6V6s. Not sure about anything else (except that a lot of them are said to rattle).

    Most reports here say that JJ's are "louder" than other 6V6s.

    380V is a breeze for ANY 6V6 new or old. Subtract the cathode voltage (in cathode biased amps) and the plate to cathode voltage (all the tube can see, and hence, is the equivalent plate voltage to an AB circuit) is even lower.

    14-15 watt dissipation is kinda lame on the designers part, but not unusual. You'll see the same or higher in original Fender 5E3s. American made 6V6GTs seem to have faired well in these amps over the last 50 years so there's no reason to assume that your GE will be any different.
     
  3. Trout

    Trout Member

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    I just pulled the back off my Richter RS 5.8 and the actual voltages are less than what you have posted. I did not recheck the 6L6 voltages but if memory serves the cathode voltage was higher.

    I have a JJ in there right now and got the following in 6V6mode.

    363V plate
    355V screen
    22.9V across the 680R cathode resistor.

    So thats roughly in the 11-12W range

    I rechecked it a few times with other NOS tubes and in some cases they read about 10% higher but still withing the acceptance range. I have no 6V6GTY's in my collection, but I do have various brand G's, GT's, & GTA's.

    If it sounds good and its not melting, Use it :D

    If you are in doubt of the physical condition of the tube, set it aside, it is not worth risking further grief later.
     
  4. Brent Hutto

    Brent Hutto Member

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    I switched back to the JJ 6V6 and the NOS 'GTY definitely sounds louder but I think that might mostly be because its tone balance is much brighter. In general my ear tends to favor brighter sounds so I kinda like it. The Champion 600 I had this particular tube in ran it so hot the top edge of the brown phenolic base actually darkened a bit. And that was with only 40, 50, 60 hours of use. Yikes!

    Trout,

    Sara mentioned the caveat that the tube voltage varies considerably depending on the mains voltage in your house. The 380V number I quoted (and 330V for the 6L6GC) were what she measured on my amp because I asked the question about how hard it drives tubes. But that was in her house of course.

    But I may be doing the arithmetic wrong. I got 37mA by dividing 25V/680ohm which I know is right. But then do you multiply that by the full plate voltage or by (380-25)? If the latter, then it's just 13.1W which is pretty middle-of-the-road by Fenderish amp standards.
     
  5. Trout

    Trout Member

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  6. Blue Strat

    Blue Strat Member

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    That's correct. The tube only "sees" what's on it's pins (plate and cathode) so it doesn't care about the plate (to ground) reading.
     

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