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Old 12th January 2013, 08:28 PM   #1
Dusk is offline Dusk  United States
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Unhappy Diy power amplifier has poping noise in one channel

Hi Folks
i built a all-tube stereo power amplifer for guitar it's 50watt a side,it's based on a Joseph Norwood design out of a 9/2008 Audioxpress,page 8,it's power by 4 6550s and i mod the PI to use one 12Ax7 instead of the 12AT7and5687 he used,also it is cathode bias,and i put a pot in the cathode circuit to make it variable,also it's in a rack case with a fan inside.Now,one side works fine,but other channel put out a internittent poping noise,not being an AMPLIFIER GURU when i hooked up the OT xfmer ,i had the primary wires reversed,It'a a Triode/Ultralinear design,i reversed the plate leads,but not the screen grid leads(not being an AMP GURU)and ran like that,like said earlier one channel worked fine,so months later i looked closer at the noisey channel found my misstake and changed s/grid wire,now the noisey channel makes this intermittenting poping noise so,this is why i am here hoping the "AMPLIFER GURU" can help me resolve the problem in the noisey channel,like i said one channel works fine,PLEASE HELPPPP

PS. each channel has one 12AX7 for it's PI, also i used feedback at each 8ohm channel output if this helps

Last edited by Dusk; 12th January 2013 at 08:32 PM.
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Old 12th January 2013, 08:40 PM   #2
chip647 is offline chip647  United States
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I doubt that your wiring reversal was the cause of your popping, however, when you soldered the tube socket during the fix, you probably created a cold solder joint between the wire and the socket. Check them and touch them up with your iron.

Then, make sure your tube sockets all have good tension and are clean. The number one cause of popping is bad socket connections.

After that, when you still have the problem, swap the tubes between channels. If the popping moves, it is one of the tubes, if it doesn't it is a part.

If it is a part, look first to the resistors and coupling caps. If these are perfect, well, the very last resort is that your OPT has a short, (but lets not go there.)
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Old 12th January 2013, 09:37 PM   #3
Dusk is offline Dusk  United States
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Smile poping noise in channel 2

Hi Chip647

Thanks for the speedy reply,i have noted the info you shared and will follow up on it,also about the OT Xfmer it's a Hammond 1650N cost me $79 a few years backs,again thanks so very much for info.

Thanks Dusk
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Old 13th January 2013, 01:49 PM   #4
Dusk is offline Dusk  United States
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Smile some pic

Hi Folks
Frist off,i know i wil catch much flak for the messey lay out of this amplifier,but i got rhe case first,and only realize i had a space nightmare when i started to populate the rack case.This is a hybrid circuit,front-end is from a guitar power amplifier in Kevin O' Connor book POP and the power sect. is from a Joseph Norwood Still circuit($450 Triode/Ultraleaner amplifier from a 8/2008 Audioxpres pg8)ok,after i get the noisy channel resolve i will move to a lager case.The amp uses 4/6550 output and2/12AX7 for PI.also 50 watta per side,one channel works fine.


it is cathode-bias with a pot the the cathode circuit to make it variable somewhat.
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Last edited by Dusk; 13th January 2013 at 01:54 PM.
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