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  • Originally posted by tyler8611 View Post
    Is 20 mA (mV) good with 451 on the plates?
    If you have 20mA of cathode current, figure about 2mA of quiescent screen current and 18mA for your plate, you at 70% dissapation. Without drawing up a load line, i’d say your probably fine.
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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    • I’ve seen 6V6s rated for both 12W and 14W. The 70% figure I quoted was at 12W.
      If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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      • Originally posted by SoulFetish View Post
        I’ve seen 6V6s rated for both 12W and 14W. The 70% figure I quoted was at 12W.
        I think your 12W figure is correct. The 14W is for the newer JJ type which seems more of a 6V6/6L6 hybrid.
        I've edited my previous post for the 12W version. If he's using JJ's, he can use the 9 over 14 = 65% figure.
        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


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        • Thanks for the help guys. The only issue I have now is this sound like speaker cone tearing (though it isn't) when I dime the vibrato channel. It is a ripping sound that spurts around after sustaining a chord. Happens with or without the effects. I've changed V2 and it's still there. Again, only happens on 10.

          The 6v6s are almost new JJs. The one nearest the rectifier has a slight blue glow around one of the spacers and the blue actually intensifies when I play a note or chord on 10.

          Guess it's either that power tube or something internal. I swapped preamp tubes and also hooked up to a different speaker with the same result.

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          • Originally posted by tyler8611 View Post
            Thanks for the help guys. The only issue I have now is this sound like speaker cone tearing (though it isn't) when I dime the vibrato channel. It is a ripping sound that spurts around after sustaining a chord...
            Issues that occur when gain is increased may be due to oscillation; closely examine the precise placement of wires in a real BF and review your lead dress against that.
            My band:- http://www.youtube.com/user/RedwingBand

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            • Originally posted by pdf64 View Post
              Issues that occur when gain is increased may be due to oscillation; closely examine the precise placement of wires in a real BF and review your lead dress against that.
              Ah that may be it! I do need to go back and recheck the lead dress anyway. Thanks, I'll see what happens, maybe take some pics and report back.

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              • I will note that, with the chassis out of the cab, it doesn't exhibit any tearing sound. I warmed the bias back up from 18 mA to 20, so it's either that or the cab that's causing it perhaps.

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                • I did barely tuck the wires into proper place but not much. They were good already. Who knows. I have it back in the cab so we'll see.

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                  • The cab is causing it, apparently. That's when it returns.

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                    • Voice 002.m4a

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                      • I can't really make out the bad noise from the soundfile, but I don't have much for speakers.
                        Often, a fault that shows up only in cabinet is due to vibration. Could be a bad tube, bad tube/socket connection, bad solder joint, dirty pot, etc.
                        I would try applying a constant signal with the chassis out of the cab, then tap around the chassis with a chopstick or rubber mallet or something and see if you can recreate the problem.
                        Originally posted by Enzo
                        I have a sign in my shop that says, "Never think up reasons not to check something."


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                        • Originally posted by g1 View Post
                          I can't really make out the bad noise from the soundfile, but I don't have much for speakers.
                          Often, a fault that shows up only in cabinet is due to vibration. Could be a bad tube, bad tube/socket connection, bad solder joint, dirty pot, etc.
                          I would try applying a constant signal with the chassis out of the cab, then tap around the chassis with a chopstick or rubber mallet or something and see if you can recreate the problem.
                          Sorry, should have had my phone closer to the amp. It's a quick tearing sound distinguishable from the natural distortion. Happens during sustained chords. I found last night it begins to occur at about 8 on volume.

                          I'll go back in and do a more thorough check. I didn't observe anything odd when I poked around the lead dress previously. Would it more likely be caused by V2 or the 6v6s?

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                          • It could be any tube. When it's doing it in the cab you can hold the tubes with a clean rag (don't burn your hand!) one at a time and see if you can make it stop. You can use a clean oven mitt too.
                            Originally posted by Enzo
                            I have a sign in my shop that says, "Never think up reasons not to check something."


                            Comment


                            • Originally posted by g1 View Post
                              It could be any tube. When it's doing it in the cab you can hold the tubes with a clean rag (don't burn your hand!) one at a time and see if you can make it stop. You can use a clean oven mitt too.
                              Playing with the chassis out of the cab, the rca 7025 i had in there was still causing it. Substituted a tung sol, which doesn't have the problem, at least not out of the chassis. We'll see what happens in the cab.

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                              • Originally posted by tyler8611 View Post
                                Playing with the chassis out of the cab, the rca 7025 i had in there was still causing it.
                                Remember we're blind-helping you here. So if you tell us the problem does not happen out of the cab then you find that it does, you've thrown us off. First thing I'd tell you it's the tubes but if it didn't happen out of the cab then obviously not, glad you found that.

                                One other thing: if this is getting worse in the cab, means that when the tubes are upside down it gets worse, then there can be mechanical problem in the tubes.

                                Also tubes are microphonic, they can be obnoxious when in a cabinet, the speaker shakes the tubes which replicate the vibration in the output, this matches what you describe when you play a chord, the underlying vibration.
                                Valvulados

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