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Post by ssyrjamaki on Jul 21, 2009 19:16:15 GMT -7
Hi, I just picked up a 6545, and I have to say that it is an amazing amp. The tone is wonderful... though it's also extremely LOUD!!! My problem is that I'm getting a lot of humming, particularly on the SRZ-65 side. I usually run the gain at about 12 o' clock - 1 o'clock, and running the Master Volume anything over 9 o' clock gives a very audible, constant hum. The tone is still great, but I'm just wondering if this is normal. The hum gets louder as the Master Volume increases. Tubes have been replaced, rebiased... It does it without the guitar plugged in. Does it through various cabs, as well as at my friend's apartment. I see that there is a JJ power cap present near on of the transformers, along with a blue cap. I assume this is not stock... Wondering if it's a cap issue, seeing as how it looks like someone might have swapped in the past. Part of me wonders if the amp hum is normal, seeinga as how the amp is just so loud The amp is great! The Doc has been wonderul, suggesting I ship it in (if need be) and answering all of my emails (right after sending them, even on the weekends). Amazing. Though I'd rather not ship it unless I have to, and local techs seem squeemish about working on botique stuff... Thank you guys for the help! Any suggestions would be great! Stephen
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Post by Paul (TRANE) on Jul 22, 2009 11:28:05 GMT -7
Hope this helps:
1. Tighten the four bottom bolts that had the chassis in the head box. 2. If the sound of the hum goes up with volume you probably have a bad tube. Since it is on the SRZ-65 side only it is probably related to one of the first 2 12AX7 Pre-amp tubes. If it were power tubes, phase inverter, or rectifier you should hear it on both side fo the amp KT-45 & SRZ-65. 3. So now take a tube that you know does not cause hum and try that tube in place of the First 12AX7 if the hum does not go away do the same with your second 12AX7. 4. If that does not fix it then I would say ship it to Dr. Z. It will perfect on return to you.
Paul G
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Post by teleric on Jul 23, 2009 21:25:09 GMT -7
Yeah, that hum is not normal. My 6545 is dead quiet on both sides. Before my last power setion re-tube, my 6545 started humming loudly. Changing the power tubes out solved my issue, but since you just re-tubed, I doubt that it's your power tubes (unless you got a bad tube).
Trane's suggestions are the way to go. Sounds like a preamp tube issue to me as well (assuming you didn't replace the preamp tubes when you re-tubed since you don't bias preamp tubes).
I have a hard time figuring how tightenting the chassis screws fixes some of the "gremlins" in an amp, but there are a few posts here on the Z board where tightening the screws has done the trick for some.
Sounds like the JJ cap is a solid state rectifier plug, but I think Trane's right on with the preamp tube suggestion (and the bolt tightening - go figure).
Try some greenbacks with the 6545. They tame the volume quite a bit (relatively low sensitivity) and go well with the 6545.
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Post by ssyrjamaki on Jul 24, 2009 6:29:17 GMT -7
Well, let's see... The amp is at the Milwaukee tech now. He's been doing this for a long time and is the town amp guru, by all accounts, so I hope he can work it out. He said he hasn't had a lot of Z's in the shop, though. I swapped all of the tubes out, including the rectifier and pre-amp tubes. still a buzz, so i changed back to the old ef86 and rectifier tubes (kept the new power tubes-- Tung Sol ef34L's-- and 12ax7's pre's in the amp). Still a hum on both channels, but definately more noticable on the 65 side, probably because of more gain...? I've noticed that the amp buzz will sometimes get louder and then goes back to the quieter hum when I lift the front of the amp up a few millimeters and drop it back down. It continues to hum, but it returns to the baseline "less noisy" hum. The louder hum might be a tube problem, since the old ef86 and rectifier tube are in the unit... but I doubt it, because I know it does this on the 65 side; as far as I know, rectifier tubes usually don't cause this type of problem, and the ef86 shouldn't affect that side of the amp... The tech thought the loud hum which stopped when I "dropped" the amp sounded characteristic of a loose connection. I hope that's it... Still, the fact that someone put a big JJ cap in there, sticking up near the transformers and tubes makes me wonder, since I don't think that is Z stock... The amp has a tube rectifier... Hmmm... We'll have to see what the tech says, and I'll let you know. As for tightening the screws-- I read posts about this on the other parts of the Z forum, and it seems to work for some. Which seems strange to me. But I took the amp apart a good 5 times and never happened to notice any changes when I put it together with snug screws... So I guess it's no dice for me... Thanks for all of the help-- I'll keep you posted! Tech was also wondering if the Doc had schematics available, if needed. Anyone know of any sites with schematic posts?
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Post by Paul (TRANE) on Jul 24, 2009 8:28:08 GMT -7
Here is why the bolt tightening helps on some noise issues. The inside bottom of the head case has a metallic film on it. If this film does not make good contact to the chassis then you can let some electrical intereference get into the wiring of the circuits of the amp. If the chassis is bolted in tight then it creates, essentially, a faraday cage that keeps unwanted electrons (interference, noise) out of the circuit components. So basically it makes a continuous metallic barrier against RFI and the like.
Paul G.
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Post by ssyrjamaki on Jul 31, 2009 18:55:11 GMT -7
Well, the amp is back from the tech. The louder hum is gone-- tech said the new tubes were "weak" in the tube reader, so he put in som JJ's...
The lower hum is still there, but he said the amp is fine. I guess it's just a bit noisy (65 channel, in particular), as it's so loud.
Great tone! Thank to all for the help along the way!
Was jamming with my buddy, who was plugged into an AC15. Sounded really good!
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