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Post subject: amp crackle
Posted: Sun Aug 08, 2010 12:13 pm
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i have a fender blues deluxe and sometimes i get a small crackle sound. it is more pronounced with the re-verb and delay on. and if i turn the presence up really high it happens more often. am i having a tube problem? the power tubes are the 6 year old original GT 6l6. and the preamp tubes are V1 TAD-12ax7 /v2 Nos RCA 12ax7a /v3 Nos RCA 12ax7a.

also i cant tell from the schematics but witch tube drives the re-verb?

some hints in the right direction would be sweet


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Posted: Sun Aug 08, 2010 1:00 pm
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1-It could be your 6L6's

2- It could be a bad solder in printed circuit
--------
Try your amp with all tubes removed , keep only in circuit your 6L6's

Power off; before removing your tubes

And power on ; with only 6L6's

If crakle, it could be one or more 6L6 or circuit around them
-----------
If no crakle, put one more tube at time and make test . Start putting the tube (12AX7 )closest to 6L6. If crakle, it could be this tube or circuit around.

If no crakle put another tube ( keep the first one in circuit).
Do that with all your tubes.


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Posted: Sun Aug 08, 2010 3:00 pm
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i think the reverb is driven through the solidstate circuit not the tubes. i have one and the tubes i use are the culprit. mine are sovtek 12ax7wa (3).some people hate them but they sound great for my set up. they are very sturdy but have the occasinal "popcorn" sound every now and then.it's not a big issue with me . i also run sovtek 6l6wxt+ power tubes whitch sound great as well. chance are it's the v1 or v2 or both dont worry about v3 its the p.i. it controls the power tubes breakup. when power tubes go bad or fail you realy know it.


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Posted: Sun Aug 08, 2010 3:04 pm
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well i swapped all the preamp tubes with new jj'S and re soldered all the tube socket connections and i still get the crackle. so i guess all it can be are the power tubes or the effects loop jacks. i will play a while with the effects loop off to see what happens.....

also is it normal to feel the transformers humming? when i place my hand on the amp i feel a humming vibration . i know its not the speaker because the volume is at 0. i don't have the best wiring in my house so could that be it?


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Posted: Sun Aug 08, 2010 6:31 pm
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I agree with Stratele, the power tubes may be worn out. But you did swap out the the PI, right ? And I'm guessing you've cleaned all the tube sockets. In a way, you're kind of stuck with trying some good tested power tubes. IMO That aspect has to be eliminated, before looking elsewhere. The transformer should be OK, as long as it's not running too hot. And I'm talking about the power trans. The output trans should not hum, and without heavy use should just be warm. Good Hunting ! Art

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Last edited by aclempoppi on Sun Aug 08, 2010 7:12 pm, edited 1 time in total.

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Posted: Sun Aug 08, 2010 6:36 pm
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yea... now i have to decide on what tubes i want lol.

and is that hum normal? its not audible i just feel it. its kinda odd. like what you feel when you place your hand on the fridge while its running and with my ear on the side close to the output transformer i can her a low hum. kinda scary like its gonna blow lol


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Posted: Sun Aug 08, 2010 7:35 pm
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Missed your post on that transformer edit. As long as the trans are not hot, it's OK ! There is 60hz& 120hz running through the amp at all times. As long as it doesn't get into the audio signal, you're fine. Is it ready to blow ? Yeah, all amps are ready to blow- that's why we use 15' guitar cords ! Art

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Posted: Sun Aug 08, 2010 8:05 pm
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Not sure if you are comfortable doing this... but usually what can cause this kinda noise is a bad cap, bad resistor, bad socket contact, bad solder point, bad circuit board tracing, arcing inside a tranny. In other words, just about anything. To find the culprit(s), I use the Old Chinese Chopsticks test.

Pull amp outta cabinet. Get a cheap WOODEN chopstick. You may wish to sharpen the tip a bit. You need to pull amp. Keep a speaker hooked up. No input (guitar not plugged in). Now, you'll need to plug amp into AC outlet. If you feel uncomfortable doing this part, take to amp tech.

Anyhow, I then prod each lead, resistor, capacitor, socket tang, etc with the WOODEN chopstick. You maybe able to find which part is making the static. I usually go from input side to power tubes-output transformer. Doesn't matter which direction, just try to go in some order to rule out each stage. Make sure that you DO NOT touch the chassis with the other hand while prodding the parts. You do not want to test the "path of least resistance" theory and get shocked by hundred of volts.

Surprisingly, this method usually finds the problem. Just remember you are dealing with 400+ VDC. Good luck with your amp.


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Posted: Sun Aug 08, 2010 9:04 pm
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well it is the output transformer i took the chassis out and turned it on and i can feel the trnsformer vibrate and with my ear close to the side the wires come out at i hear buzzing and electrical humm.... how long do i have :shock:


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Posted: Sun Aug 08, 2010 10:36 pm
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Was the speakers hooked up to the output tranny? OPT's no like being unloaded and can hum. If OPT was hooked to speakers and you get hum... could be a number of things. The power tranny doesn't hum? I usually get PT humming when outlet power is too low voltage.

Could be main filter cap(s) gone bad. Bad coupling cap(s). Bad tranny. At that point, prolly best to take the amp to amp tech.


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Posted: Sun Aug 08, 2010 10:47 pm
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yea the speaker was hooked up and a gray disc cap looks cracked next to all of the transformer connections i really cant afford to get it fixed :(


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