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Dannyboyee82

Epiphone Blues Custom 30 Crackling

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Hi everyone, thanks for taking a look at my thread.

 

I bought the Blues Custom this week and this morning I noticed a quiet, but still annoying crackling coming from the speakers. It doesn't get louder as you turn the volume up. I thought it might be one of my pedals (Sonic Stomp and Boss BD-2), or maybe the guitar itself but the crackling is still present when I unplug the guitar and all effects. Does anybody know what could be causing this?

 

Be aware, I am a total beginner when it comes to amps and this is my first valve amp so if you do know the cause could you please explain it in a simple way! Thank you!

 

Danny

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Hi everyone' date=' thanks for taking a look at my thread.

 

I bought the Blues Custom this week and this morning I noticed a quiet, but still annoying crackling coming from the speakers. It doesn't get louder as you turn the volume up. I thought it might be one of my pedals (Sonic Stomp and Boss BD-2), or maybe the guitar itself but the crackling is still present when I unplug the guitar and all effects. Does anybody know what could be causing this?

 

Be aware, I am a total beginner when it comes to amps and this is my first valve amp so if you do know the cause could you please explain it in a simple way! Thank you!

 

Danny[/quote']

 

Could be some noise coming in on the lines. Any superimposed noise on the 120v will pass right through

the power transformer and caps and be present on the B+ for the tubes.

 

Could also be a tube. Some tubes can go noisy and "crackle"...make sure that

the efx is unplugged from the amp and the reverb is turned down.

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Ok, so if I understand you correctly it could be something completely separate from the amp that is somehow making the noise, or it could be a dirty tube? When you say efx, do you mean effects pedals?

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Ok' date=' so if I understand you correctly it could be something completely separate from the amp that is somehow making the noise, or it could be a dirty tube? When you say efx, do you mean effects pedals? [/quote']

 

I wouldn't necessarily call it a "dirty tube" as tubes generally don't go defective

that quickly. I suppose it can happen though, the term is called "infant mortality"

in the electronic industry where a component can fail long before it's expective

live time.

 

The crackling/"sputtering" you are hearing can come from anywhere.

Inside the amp or external to the amp. The problem of course is that in order to hear it, you need to keep

the volume at a reasonable level and that also includes components within

the amp..

 

components that can cause noise inside the amp are:

 

resistors (especially the carbon composition type)

power supply to some degree..especially if it's got a tube rectifier

controls. (volume, tone etc)

tubes..

 

things that can cause noise outside the amp via power lines can

be just about anything.

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I have turned everything off in the house and just had the amp on alone, no guitar plugged in and it still crackles. Also, it was doing it at my friends house earlier today. So, by the process of elimination it seems like it is something inside that amp that is causing it. Where would you suggest I go from here? Is there any other information you need that I have left out? When I turn the reverb up you can really hear the crackling, it sounds awful.

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I have turned everything off in the house and just had the amp on alone' date=' no guitar plugged in and it still crackles. Also, it was doing it at my friends house earlier today. So, by the process of elimination it seems like it is something inside that amp that is causing it. Where would you suggest I go from here? Is there any other information you need that I have left out? When I turn the reverb up you can really hear the crackling, it sounds awful. [/quote']

 

 

At home there isn't that much you can do other than replace the tubes.

You need to get a tube layout of your amp and start pulling tubes at least the 12ax7

one by one.

 

Start with the channel preamp tube (12ax7) Turn the power off and pull it.

 

You can also pull the reverb spring driver (12ax7) and then the reverb spring

preamp (12ax7). The reverb is a separate circuit.

 

It the noise goes away..maybe the cause is the tube or something in the preamp

section. This particular amp uses 2 or 3 relays. One of the relays is in the power

tube section (5881) and depending on whether it is activated or not..takes

the screen grid and either connects it to a power supply or through a 5 watt

dropping resistor.

 

Relay contacts are never a good thing in a power amp design. Sooner or later

a relay contact can become intermittent and you could get noise, especially

when you have a fair amount of B+ tube current going through the relay contacts.

 

Unfortunately, you will not be able to pull the 5881s, because you will hear nothing

then. It's a crude test and it's a last resort. Buying a set of tubes and substitution

is the proper way..or take it in to repair shop and have someone open up the

chassis and use a oscilloscope probe to look at the static dc levels. Any noise

or sputtering will show up quickly and an experienced tech can work backwards

from the power section towards the preamp section.

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Ok, so I had a look at the preamp tubes tonight. All are 12AX7EH Electro Harmonix by the way. I don't really know why but there is a row of three and then a row of two. I began with the row of three, to make it easier I will name the tubes a, b and c. The first tube I pulled, a, didn't make any difference. But when I pulled b, the crackling went. I kept on with my test though. After returning tube b to the socket and pulling tube c, the crackling wasn't present either. I'm sure you will understand why that is. On the row of two, pulling the tubes from there made no difference.

 

What do you suggest I do? Replace both tube b and c? Or just buy one tube to replace either b or c?

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As funny as this may sound, the simple act of pulling the tubes and reseating them may have been all that was needed to provide a clean connection and stop the annoying crackling sound.

 

If the crackling returns, you already have the general problem area isolated.

 

Still, it might be in your best interest to pick up a pair of spare tubes ( I would recommend the JJ brand) to have on hand to switch out in case the crackling returns.. Even if the crackling does not return, the spare tubes will definitely come in handy at some time.

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Sorry, I've just realised how my last post sounded. I'll try explain a bit better.. the crackling is still there, reseating the tubes hasn't changed anything. But, in the row of three pre amp tubes that I pulled out, if I pulled the middle one OR the one on the right out, the crackling disappeared. Putting them back in brought the crackling back. What I found strange was that, for example, pulling the middle one out got rid of the crackling.. but putting the middle one back in and pulling the right hand side one out also got rid of the crackling. So, the tube I just pulled that got rid of the crackling is now back in, I've pulled a different one out and that also stops the crackling. But, put them all back and the crackling reappears. Do you get me? I didn't explain properly in the last post! Do you think I should replace both those tubes, or just one? Or do you think it is something other than the tubes?

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Sorry' date=' I've just realised how my last post sounded. I'll try explain a bit better.. the crackling is still there, reseating the tubes hasn't changed anything. But, in the row of three pre amp tubes that I pulled out, if I pulled the middle one OR the one on the right out, the crackling disappeared. Putting them back in brought the crackling back. What I found strange was that, for example, pulling the middle one out got rid of the crackling.. but putting the middle one back in and pulling the right hand side one out also got rid of the crackling. So, the tube I just pulled that got rid of the crackling is now back in, I've pulled a different one out and that also stops the crackling. But, put them all back and the crackling reappears. Do you get me? I didn't explain properly in the last post! Do you think I should replace both those tubes, or just one? Or do you think it is something other than the tubes?[/quote']

 

 

Like I mentioned before, pulling tubes to isolate a problem is a very crude method and sometimes can

lead to confusion as to the cause.

 

I haven't been able to find a tube layout for this amp, but I did find the schematic for it.

You can find it here..

 

http://www.ppwatt.com/files/ppwatt/EPIPHONE_BLUES_CUSTOM_30_SCHEMATIC_VER01_DPPT.pdf

 

Basically, this is a 30 watt amp that can operate in Class A/B (pentode mode = 30 watts) or

Class A (triode mode = 15 watts). In the schematic there is a switch (S5) that connects the screen grid

to a large 5 watt resistor in pentode mode, or to a special power supply tap in Triode mode, so the

5881 (6L6) can be used in either mode.

 

There is a 12ax7 (ECC83) preamp tube (V1A/V1B) and another one V2A/V2B in the EQ section.

There is a 12ax7 (v4a/V4b) that serves as the drivers for the power stage.

 

There are two separate 12ax7 used for the spring reverb (V3a/[confused] pre reverb amp and (V5a/B)

post reverb amp. These have the unusual distinction of being coupled together in parallel.

I suppose it's better than leaving a part of the dual triode just hanging there without any bias

and essentially the dual triode functions as one triode.

 

I'm not sure from your description and troubleshooting method that you have managed to isolate

which stage is causing the crackling problem.

 

If the final 5881 stage can operate as a triode..try switching it to class A mode and see if the crackling

goes away..at least then you have isolated it to the more common failure (power tubes).

If the crackling goes away, then it is (more than likely) one of the power tubes..and those should

really be replaced as a pair..because what has caused one to fail may have weakend the other.

 

 

If not, then the problem could be anywhere in the preamp chain...V1, V2 or even driver V4.

 

It could also be in the reverb pre/post 12ax7s.

 

So as I explained, there is only one more option available to you.. besides replacing the tubes.

1. Push all buttons (EQ) a few times to see if it's a button contact that is intermittent and generating the

noise. 2> Operate the foot switch a few times. 3. Go to class A mode. 4. Flip all slide switches a few

times to see if it's an intermittent switch contact.

 

5. Having done that, replace the tubes, starting with the power stage first.

 

 

If the noise continues, then it could be coming from anywhere inside the amp..COLD SOLDER JOINT OR

A LOOSE COMPONENT (lead not making proper electrical contact) tube sockets,power supply rectifier, filter caps, preamp stage components, switches, relays etc.

 

The only thing then is to scope out each stage to see which stage is generating the noise. Once the stage is identified, then scoping the individual elements of the tube around those stages would give some indication of where the noise spikes (cracking) is coming from. Then the the defective component can be identified and replaced.

 

This will require an audio technician familiar with the schematic for this amp, tube pinouts and knows how to use an oscilloscope and can remove and replace the component.

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Ok, first of all, thank you Carverman for taking the time out to respond to my messages. Secondly, this is all a bit confusing to me really, this being my first valve amp and not having any knowledge of electrics. I have got in touch with my local luthier today to see if he knows anybody in the business of fixing amps. In the meantime I might as well replace the power stage tubes. I have read that a good replacement for the power stage would be a pair of 6L6GC tubes. Can you recommend any good ones?

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I might as well replace the power stage tubes. I have read that a good replacement for the power stage would be a pair of 6L6GC tubes. Can you recommend any good ones?

 

 

It probably wouldn't be a bad idea as the first stage of actual troubleshooting.

Years ago when TVs had lots of tubes, that is the FIRST thing that any repair

tech did to try and fix a symptom. It didn't always work, but it's a time saver.

No use looking for troubles inside until you have covered the basics at least,

and tube substitution is something you CAN do yourself at home.

 

Here is a comparo of the 5881/6l6GC. I have 6L6WXTs (Sovtek) in my Peavey

Valveking that came standard with the amp and they are nice and quiet and

I can also run them in a modified class A configuration and they sound very

good in that mode.

 

However..be warned that even though the 6L6GWC ( or other suffixes)

may plug into the octal socket, not all 6L6 can handle the plate voltages that

the 5881 is designed for and may actually overheat!

 

There is probably a reason the industrial version of the 6L6 was used in

this particular amp, so I would try and sub a set of Tungsol 5881s in there first,

because you don't need any bias changes and if they are running CLASS A mode,

you might just want to keep the same tube specs in there.

 

The plate power dissapation should be the same, you will get more saturation

headroom to drive the o/p transformer andyou will get longer service and reliability

than with a 6L6GC. Although having said that..6L6GC will take a Lot of abuse

in tube amps before actually giving up the ghost. I have seen them glow a dull

red in the plate and still work!

 

Read the info on the 5881/KT66 before making a decision.

 

http://www.audiotubes.com/6l6.htm

 

 

and here's some more good tube comparison info..

 

 

http://thetubestore.com/6l6templeton.html#summary

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Ok' date=' so if I understand you correctly it could be something completely separate from the amp that is somehow making the noise[/quote']

Possibly... I have an epiphone firefly 30 dsp (30w solid state, 10" speaker) that hums when I touch a radiator...

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Yet again, thank you. I've got the amp booked in tonight to be repaired. The guy who is doing it will diagnose it for free, let me know what is wrong and give me an estimate before going ahead with any work. He only charges £10 per hour, plus parts at cost price. £10 is around $15. I'll let you know what the outcome is.

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One quick question - Did Epiphone change the spec on the output valves at some point because I see people talking all the time about 5881's yet mine came straight from Epiphone (via a main dealer and Gibson Europe that is) fitted with 6L6GC's ?

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One quick question - Did Epiphone change the spec on the output valves at some point because I see people talking all the time about 5881's yet mine came straight from Epiphone (via a main dealer and Gibson Europe that is) fitted with 6L6GC's ?

 

 

Essentially almost the same tube...

 

here's some specs on both.

http://thetubestore.com/6l6templeton.html#summary

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Hi Carverman

 

I appreciate that they're essentially the same (some minor differences) but I was querying simply becasue most people's BC30's seem to have been fitted with 5881's whereas mine came fitted with Sovtek 6L6WXT's (I stated that they were 6L6GC's in my post in error) which, according to the link you supplied, ISN'T a repackaged 5881.

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Hi Carverman

 

I appreciate that they're essentially the same (some minor differences) but I was querying simply becasue most people's BC30's seem to have been fitted with 5881's whereas mine came fitted with Sovtek 6L6WXT's (I stated that they were 6L6GC's in my post in error) which' date=' according to the link you supplied, ISN'T a repackaged 5881.

 

[/quote']

 

Pretty much most amps these days are assembled in China, my Peavey Valveking 112 has Sovtek 6L6WXT

so I'm not surprised that Epiphone amps have similar tubes. The factories buy whatever is the cheapest

and probably the 6L6WXT are the cheapest tube right now. Nothing wrong with them either.

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I was just wondering if perhaps Epi had made an active decision to go over to the 6L6's a couple of years ago when I bought mine.

 

I agree the Sovteks aren't too bad - not a patch on the NOS early 60's RCA Balckplates I replaced them with though [blush]. Those teamed up with the Mullard GZ34 make it sound really sweet though I'm not sure I'd want to keep them in there if I was gigging the amp - bit like using a vintage car as a daily driver, enjoyable but ultimately very expensive!

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I've occasionally had a problem with crackling too. It happens most often when I turn the amp off, but sometimes it happens when I'm just playing. At one point it just seemed to happen when I hit certain notes (A if I remember right). That problem has gone away though.

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I've occasionally had a problem with crackling too. It happens most often when I turn the amp off' date=' but sometimes it happens when I'm just playing. At one point it just seemed to happen when I hit certain notes (A if I remember right). That problem has gone away though.[/quote']

 

 

Some amps when you turn them off will "pop" due to the filter caps discharging through the tubes creating a

momentary dc transient.

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Thanks for everyone's help on this issue. I've had the amp looked at and the guy I took it to found that it was the transistors in the reverb stage that was causing the problem. A simple case of replacing the parts for new ones. He also found that the amp was humming a little. This was also to do with the reverb stage. He said that the way the amp was designed, with having the reverb stage so tightly crammed together, was causing it to feedback through the speakers. Again, a fairly simple remedy of shielding the reverb tank. I get to pick it up tonight. Can't wait!

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Thanks for everyone's help on this issue. I've had the amp looked at and the guy I took it to found that it was the transistors in the reverb stage that was causing the problem. A simple case of replacing the parts for new ones. He also found that the amp was humming a little. This was also to do with the reverb stage. He said that the way the amp was designed' date=' with having the reverb stage so tightly crammed together, was causing it to feedback through the speakers. Again, a fairly simple remedy of shielding the reverb tank. [/b']I get to pick it up tonight. Can't wait!

 

So are these are the Belton reverb units..made in Korea?

 

I would have thought that the reverb pan/tray would be located at the bottom of the amp away from the tubes and speaker.? The older spring reverb pans used to have padding around them to prevent acoustic feedback from

affecting the springs. Everyone knows about the thunderous "crash" if you jolt the amps with the reverb unit on.

 

Looks like some of these newer tube amps use OEM parts from Korea/China and the reverb unit design uses

transistor stages for impedance matching or drivers.

One has to wonder why they bothered putting in TWO 12ax7 tubes as a pre/post reverb stage in this Epiphone

amp? Two tubes basically doing nothing?

Unless they are used as impedance matchers into the driver stage of the amp.

 

Perhaps during the design stage of this amp, they were going to use the traditional 2 or 4 spring pans,

then changed their minds after getting a "cheaper bulk deal" from the reverb unit manufacturer?

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