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Post by zone47 on Jul 3, 2007 4:58:51 GMT -7
....or is it the other way around? Seems to me that one could be used in place of the other, but not the other way around. I have another Dr. Z with a Sovtek 5AR4 rectifier and I just don't trust the Sovteks.
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Post by zdogma on Jul 3, 2007 6:13:10 GMT -7
Yes, its fine, but you will need to rebias if its a fixed bias amp.
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Post by zone47 on Jul 4, 2007 8:07:25 GMT -7
I'm talking rectifier tubes.... changing those would change the bias on the power tubes?
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Post by benttop (Steve) on Jul 4, 2007 8:14:02 GMT -7
I'm talking rectifier tubes.... changing those would change the bias on the power tubes? Changing to a different rectifier changes all of the power supply outputs including the bias output. So for those amps that require the bias adjustment, they would have to be checked and reset.
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Post by zone47 on Jul 4, 2007 9:56:13 GMT -7
Oh, that's interesting... I didn't know that. The head is a Mesa heartbreaker... and it is fixed bias. I was hoping to steal the 5AR4 to replace my Sovtek 5AR4 in one of my Dr. Z heads since I don't have a good track record with Sovteks. I have several 5U4 GBs laying around.
I guess I could always pop a 5U4 GB in the Prescription ES and then re-bias it, but wonder if that would soften or tighten the sag? ... or if it would remain about the same?
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Post by billyguitar on Jul 4, 2007 10:28:46 GMT -7
Just try it. If it sounds fine then I wouldn't worry about it. I think a 5U4 draws more current but Fender used them on different amps that used the same power transformer. My general feeling is that a 5U4 is a 'slower' rectifier tube and may induce a little bit of sag but I doubt you'd notice it in a Boogie.
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Post by benttop (Steve) on Jul 4, 2007 10:57:22 GMT -7
Oh, that's interesting... I didn't know that. The head is a Mesa heartbreaker... and it is fixed bias. I was hoping to steal the 5AR4 to replace my Sovtek 5AR4 in one of my Dr. Z heads since I don't have a good track record with Sovteks. I have several 5U4 GBs laying around. I guess I could always pop a 5U4 GB in the Prescription ES and then re-bias it, but wonder if that would soften or tighten the sag? ... or if it would remain about the same? RXES is cathode biased I believe. See the discussion of bias on the Dr. Z Webpage at www.drzamps.com/biasnotes.html - it's a bit out of date as it doesn't include some of the newer fixed bias amps. Also check this discussion of rectifiers from the Doc at drzamplifiers.proboards41.com/index.cgi?action=display&board=xperts&thread=1167267254&page=1
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Post by zone47 on Jul 5, 2007 5:38:18 GMT -7
Oh, that's interesting... I didn't know that. The head is a Mesa heartbreaker... and it is fixed bias. I was hoping to steal the 5AR4 to replace my Sovtek 5AR4 in one of my Dr. Z heads since I don't have a good track record with Sovteks. I have several 5U4 GBs laying around. I guess I could always pop a 5U4 GB in the Prescription ES and then re-bias it, but wonder if that would soften or tighten the sag? ... or if it would remain about the same? RXES is cathode biased I believe. See the discussion of bias on the Dr. Z Webpage at www.drzamps.com/biasnotes.html - it's a bit out of date as it doesn't include some of the newer fixed bias amps. Also check this discussion of rectifiers from the Doc at drzamplifiers.proboards41.com/index.cgi?action=display&board=xperts&thread=1167267254&page=1Good stuff! Thanks.
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