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Got a 5e3 with 6L6's that I built and it sounds great exept for the bad hiss, and that it has a faint hum that stops when I touch the chassis, switch etc. I tried putting 1/2 watt metal film plate resistors on the preamp but it didn't help. Tried every tube I had with some beieng better but still bad. I've used carbon comps through out and mallory 150's, spragues, CTS pots,switchcraft jacks. My layout is very neat and grids are short but not sheilded. All solder joints seem to be good. Could it be other noisey cc's? What are other likely problems?
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Well two things. One is I'd be real care full running 6L6's with that amp unless you have a higher wattage Output tranny than what came with the kit. They aren't to stout and may blow it at high volumes. Two is it sounds like you definitely have a grounding issue and a pot may not be grounded. Check all of your pots and make sure they are grounded and also check the input jack and make sure the sleeve is grounded. mismatched tubes that are real far apart may do it but the touching the amp grounding it out makes me think it's not that. You could also have something wired wrong not going to ground that should be.KB -
Hey KB.
Of touching the chassis makes hum go away, I'd also say yo have a grounding issue. Three wire cord? Hope so. All pot body rear covers grounded to chassis? Hope so.
Hiss comes from somewhere, so isolate it. Do the controls affect the volume or tone of the hiss? If so it is coming in before them, and if not it comes in after them. Or pull the preamp tube. Does that kill the hiss? If so, you found the general area of its source. Once you determine the stage sourcing the hiss, it is then a lot easier to eliminate. Hiss and gain go hand in hand.Education is what you're left with after you have forgotten what you have learned.Comment
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I'm using the mercury magnetics OT that is for 6v6 or 6l6 and the tubes are supposedly matched pair of jan 6L6WGB's I wired the 2 grounds at filter caps and the 3 prong cord and centertap on power trans bolt and the pots and cathodes are grounded on the ground leg of a switchcraft input jack. I've built a 6v6 deluxe in the same fashion except for the tubes OT, and went to a 10 watt bias resistor. The other is very quiet and I didn't use any sheilded wire and also used all carbon comp resistors. The noise is definately coming from the first stage on both channels. Not sure why one is quiet and other is so hissy. The hum is barely audible, but I just can't live with the hiss. BTW I don't remember it having any hum when I first fired it up, but I'm not for sure.Comment
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Well as Enzo said gain and hiss go hand N hand but that is usually the case with high gain amps however they are proportional. The 5E3 being as clean as it is shouldn't have any hiss at least mine doesn't. Another thing that can cause this is a wire around the heater wires that is picking up the AC. You did twist the wires from tube to tube right ? You may try moving them around and see if you can hear a change. It usually buzzes more than a hiss. The 5E3 isn't an amp that has enough cascaded stages to hiss so Enzo may be unto something here.KBComment
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tried switching the preamp-tube witht he phase-inverter...how about swapping with the amp that doesn't hiss?
Are you using a 12AX7 or 12AY7 in the pre-hole....the 'Y7 would be much quieter hiss-wise...Comment
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I twisted the wires and they are straight up and all other wires are tight to the chassis. Also I've got A NOS 12AY7 in the pre and a EH 12ax7 for the driver. I tried lots of other tubes including ones from my other ultra quiet 5e3 with 6v6. What would be causing the hum to stop when I touch the amp? And aren't metal film resistors on the plate supposed to be more quiet as far as the hiss?Comment
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Originally posted by tubelovin
Well, bad grounding of the chassis would cause the hum to go away when you touch the chassis (you're grounding it with your body) I'd say remelt the solder on the green wire, spreading as much as you can.
As for the hiss http://www.geofex.com/ampdbug/hiss.htm
Bye.
Max.Comment
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I remelted my ground with no end to the hum. I've measured all grounds and there isn't any resisitance on my meter. I don't know that i meens anything but when I touch the chassis on the side that the pots are mounted it makes a louder tapping sound than the rest of the chassis.
When poking one of my coupling caps with a chopstick it makes a louder tapping noise compaired to all the others. If I can find a spare I will replace it. Do you think that it could be a source for the hiss? It's got to be before the driver becase the hiss gets louder with volume. I thought it would be the 100k plate resistors but I chaned those to metal film? It's frustrating to have the amp sound so good otherwise and not want to play it because of these problems.Comment
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