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Old 27th December 2005, 01:10 PM   #1
Noak is offline Noak  Singapore
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Default Tube Amp - Crackling Sound on Left Channel

hi all,

I have a tube headphone amp that's giving me some problems recently. The headphone amp uses an input 12AU7, a driver 12AX7 and a pair of EL84 power tubes.

With some tube combinations, the left channel will emit a random crackling (tsk....tsk...ts...kkk) sound. Is it DC leakage?

For combinations that worked fine:
Amperex ECC82 + Telefunken ECC83 + Valvo EL84 or Amperex EL84
Amperex ECC82 or Brimar 13D5 + Brimar ECC83 + Valvo EL84

For combinations that emit random crackling sound:
Brimar 13D5 + Telefunken ECC83 or Valvo ECC83 + Valvo EL84
Amperex ECC82 + Valvo ECC83 or Philips Miniwatt ECC83 + Valvo EL84

For combinations stated above, the results were highly repeatable and I do have pairs for some of them and I rolled in the 2nd set as well. However, the most consistent of all is that the noise only comes from the left channel.


Please advise. Thanks in advance.
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Old 27th December 2005, 02:13 PM   #2
Giaime is offline Giaime  Italy
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Hello Noak,

provided that you've double checked all of your wiring and all of your passive components, sockets included, you've got bad tubes I think.

I either had a cracking sound on the left channel of my tube preamp, I was running AC heaters. When I converted them to regulated DC, the noise went away. Also regulated HV helped a bit.
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Old 27th December 2005, 02:43 PM   #3
Noak is offline Noak  Singapore
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hi Giaime,

Thanks for the input. I've yet to check the wirings and the passive components.

I can't think that it's the tubes because from my combination stated above, I can't even pinpoint exactly which tube is at fault and I do have and tried more than one of the same tubes.
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Old 27th December 2005, 03:16 PM   #4
Giaime is offline Giaime  Italy
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Default Re: Tube Amp - Crackling Sound on Left Channel

Quote:
Originally posted by Noak
For combinations that worked fine:
Amperex ECC82 + Telefunken ECC83 + Valvo EL84 or Amperex EL84
Amperex ECC82 or Brimar 13D5 + Brimar ECC83 + Valvo EL84

For combinations that emit random crackling sound:
Brimar 13D5 + Telefunken ECC83 or Valvo ECC83 + Valvo EL84
Amperex ECC82 + Valvo ECC83 or Philips Miniwatt ECC83 + Valvo EL84
Hi Noak,

if I understand well, you have all good EL84, all the ECC82/13D5 (are you sure about this one? 13V is different than 12.6V, althought it seems to me that it will perform fine...) and good Brimar ECC83. Bad ones are Philips and Valvo ECC83. But as you say, even with Telefunken ECC83 you're getting noise... I would look at the sockets, are they new or refurbished from old equipment?

Also take a look at the resistors you're using, even with small dissipation across them, in hi-volt places is best to use 1W or more resistors. 1/4W ones many times can't stand even 100 or less volts, even if the P dissipated is smaller than 1/4W.
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Old 27th December 2005, 04:29 PM   #5
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Sounds like dodgy valves to me also.
Would check for mechanical/passive problem too.
With unit turned on and attenuated, try and tap boards, bases and wiring intersections with pencil, plastic pen etc. you can often find electronic failures (microphonic caps) intermittent electrical contact etc. and generally isolate where in circuit this is with no test equipment. But be careful, valve ht's bite
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Old 28th December 2005, 01:13 AM   #6
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I have chased snap crackle pop sounds in my 300Beast amplifier for two years without success. It goes away for a few days or longer whenever I change tubes. Even if I switch the left and right channel driver tubes the noise goes away for a few days. Then when the noise returns, I swap them back, the noise goes away again. I have decided that it is either the resistors, or the tube sockets. Either way the repair is worse than the problem, since both are mounted on a home made PC board that has been soldered on far too much.

In my previous life fixing amplifiers I have found that noise like this can come from a few different sources. Tubes, resistors, tube sockets, and capacitors in that order. A tube with a leakage from heater to cathode will often cause a frying or hissing noise that may change as the tube gets hot. A tube may also cause a loud pop due to internal elements moving as they expand due to heat. A resistor will often cause noise as it internally breaks down. As mentioned before some resistors were never meant to operate at the voltages that we give them. Think of the sound that a very small internal spark inside a resistor will make, then amplify it. Tube sockets can cause all sorts of strange noises, although wiggling the tube will usually quiet them down for a while. Often a SMALL amount of WD40 will fix them. A capacitor that is breaking down usually causes a pop, and a leaky capacitor usually causes distortion. Often the distortion gets worse with heat.

Sometimes the bad component can be found with a can of freeze spray. Spray the suspected component for a second or two, with the amp running, and wait for a minute to see if the noise changes. Sometimes a hot soldering iron can be used to find a bad part. Just be careful not to touch a component lead, or you will have more problems.
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Old 28th December 2005, 01:17 AM   #7
GaryB is offline GaryB  United States
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I've problems with crackling noises in capacitor coupled single ended tube amps related to the coupling capacitor going bad and then taking out the plate resistors. So I'd suggest changing out both coupling caps and plate resistors and seeing if that had any effect.
---Gary
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Old 28th December 2005, 01:46 AM   #8
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Intermittent faults like this are infuriating.

It's likely to be due to a poor electrical connection somewhere, e.g. dry solder joint or a joint making point-contact connection, dirty tube sockets, dirty tube pins. I have sometimes been able to find a bad connection by tapping different parts of the circuit with a plastic knitting needle.
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Old 28th December 2005, 01:46 AM   #9
Noak is offline Noak  Singapore
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Default Re: Re: Tube Amp - Crackling Sound on Left Channel

Quote:
Originally posted by Giaime

Bad ones are Philips and Valvo ECC83. But as you say, even with Telefunken ECC83 you're getting noise...
Yes, that's the dilemma I'm in. What's the chances of having 6 tubes all with problems in the left channel only?

Quote:
Originally posted by Giaime

I would look at the sockets, are they new or refurbished from old equipment?
Bought the amp new 3 yrs back, the socket should have been new then. On closer inspection, I do see that some of the metal plate contacts within the sockets aren't aligned well.

Quote:
Originally posted by bernification
With unit turned on and attenuated, try and tap boards, bases and wiring intersections with pencil, plastic pen etc. you can often find electronic failures (microphonic caps) intermittent electrical contact etc. and generally isolate where in circuit this is with no test equipment. But be careful, valve ht's bite
Thanks for the advice, bernification. I had almost been bitten by valve's ht so I will take extra precautions.

Quote:
Originally posted by tubelab.com
In my previous life fixing amplifiers I have found that noise like this can come from a few different sources. Tubes, resistors, tube sockets, and capacitors in that order. A tube with a leakage from heater to cathode will often cause a frying or hissing noise that may change as the tube gets hot. A tube may also cause a loud pop due to internal elements moving as they expand due to heat. A resistor will often cause noise as it internally breaks down. As mentioned before some resistors were never meant to operate at the voltages that we give them. Think of the sound that a very small internal spark inside a resistor will make, then amplify it. Tube sockets can cause all sorts of strange noises, although wiggling the tube will usually quiet them down for a while. Often a SMALL amount of WD40 will fix them. A capacitor that is breaking down usually causes a pop, and a leaky capacitor usually causes distortion. Often the distortion gets worse with heat.

Sometimes the bad component can be found with a can of freeze spray. Spray the suspected component for a second or two, with the amp running, and wait for a minute to see if the noise changes. Sometimes a hot soldering iron can be used to find a bad part. Just be careful not to touch a component lead, or you will have more problems.
hi tubelab.com, thanks for providing the valuable advices. I will perform a thorough check tonight.


Quote:
Originally posted by GaryB
I've problems with crackling noises in capacitor coupled single ended tube amps related to the coupling capacitor going bad and then taking out the plate resistors. So I'd suggest changing out both coupling caps and plate resistors and seeing if that had any effect.
---Gary
hi Gary, thanks! Seem to me that I would have to watch out for the resistors, tube sockets etc.
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