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Post by Deleted on Mar 26, 2008 4:52:17 GMT -7
I searched back 1 year looking for info on balanced triodes and couldn't find anything. I hope this hasn't been beat to death!
I just bought a used MAZ 18 and I'm retubing to make sure I'm starting with fresh tubes. I've been playing through vintage Fender amps, so I'm familiar with KCA and how NOS tubes can have a positive effect on tone. What I don't understand is why I need balanced triodes for the phase inverter.
Can someone explain why, and what would happen if you didn't use a balanced triode tube for the PI?
Thanks in advance!
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Post by amakitalo on Mar 26, 2008 9:02:40 GMT -7
The signal you hear from your amp is a really a sin wave, with your one power tube creating the up side, if you will, and the other power tube creating the down side. If your power tubes are not matched the the wave in the up side is different from that of the down side resulting in crappier tone.
The PI drives your power tubes. It has two sides, one driving one tubes and the other driving the other tube (in a two power tube configuration). If the sides of your PI are wildly different, they push even a well matched pair of power tubes at different levels creating an out-of-whack sin wave and thus a crappy tone, or crappier tone. There is an audible difference, at least between PIs that are matched and those where the two sides of the triode are very different.
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Post by Deleted on Mar 26, 2008 9:26:05 GMT -7
Thanks for the response. It helps to know why! I ordered a couple 12AX7's from KCA that have balanced triodes, so I'll see if I can hear a difference.
I heard that Dr Z doesn't ship their amps with balanced triode tubes in the PI slot, since it'd be too hard to find that many balanced triode tubes. I assume that's true, as it kinda makes sense. Based on that, I assume the suggestion to go with balanced triodes is a user/tweaker suggestion (which I can definitely appreciate), like using an NOS rectifier tube?
Thanks again!
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Post by amakitalo on Mar 26, 2008 10:40:35 GMT -7
For sure user/tweaker thing. Funny this came up; yesterday I was playing with my Stangray that I just got a week or so ago. It sounded good. Then I put in a balanced LPS from Mike and I actually heard a difference. It wasn't that the tone before was bad at all. In fact it was great, but after putting the new PI in it was somehow smoother and more pleasant. I kept swapping the tube to make sure this just wasn't in my head. It wasn't, the tone was better to my ears.
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Post by edoetsch on Mar 30, 2008 10:41:38 GMT -7
this worries me as i've just thrown in a 12ax7 i had lying around into my route 66.
what are the chances it is off balance?
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Post by Deleted on Mar 30, 2008 12:01:32 GMT -7
From what I've gathered, it's almost certain that tube would not be balanced. I assume nothing bad can happen to your amp, though, since it's highly doubtful Dr Z puts balanced triode tubes in the phase inverter slot of every amp that rolls out the door.
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Post by amakitalo on Mar 31, 2008 12:01:23 GMT -7
There is no reason to worry if your PI is not balanced or matched. Nothing will break and as for the tonal differences, I believe they are subtle. I think it was Myles that said that a good PI can make a good sounding amp sound great.
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Post by myles on Apr 1, 2008 19:23:26 GMT -7
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Post by rhythmeister on Apr 29, 2008 14:37:54 GMT -7
Just thought I'd throw in a comment here. I was getting some rather "rough" distortion from my Roccaforte HG100 and it dawned on me that this was one of my amps where I hadn't put a balanced tube in the PI. I just had a new JJ 12AX7 in the PI position - but not a balanced one. Went through my box of tubes and found a Westinghouse USA 5751 tube. After reading Myles' comments (he linked in his post above), I gathered that an older 5751 would likely have a better balance for PI use. So I popped that sucker in the PI slot and the amp sounds much, much better. I mean like 25-50% better (don't ask me to tell you how I came up with those numbers ) But it definitely went good to great. Cheers, Blair
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Post by bustertheboy on Apr 29, 2008 23:07:08 GMT -7
I think the balnace PI is a good idea, but interestingly I've seen mods going the other way for Black Face Fenders- you intentionally increase the imbalance to roughen up the signal- weird in a way! Brett
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Post by ajnewkirk on Jun 20, 2008 0:29:10 GMT -7
Be sure to read the PDF file that is linked to at the bottom of the page Myles mentioned above. It made me actually start thinking about the PI tube.
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