#1
But i can't work out where it's coming from, I have a feeling the problem stems from my OD pedal but I can't be sure.

At the moment I'm just going

Epiphone Les Paul Standard -> Visual Sounds double trouble -> Fuzz -> Marshall JCM900
Send ->Boss GE-7 -> Return

I get the feedback when I'm using both sides of my Double Trouble, side 1 is volume full up and drive 1/4 way round, side 2 is just used for a boost. I found this is the best way to get my sound out of it but it does feedback like a bastard with them both on and my amp on at a reasonable volume.

Would I be better off selling the Double Trouble and getting a new OD pedal and something like an LPB-1?
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#3
^I have no idea if I'm honest. Haven't really looked at the tubes because I don't know what I'm looking at
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#4
Well here is a pretty simple test to add to your process of elimination.

The preamp tubes are the smaller ones usually inside those aluminum cylinder casings right.

Take those off. Personally, I just leave mine off as I've never experienced a problem. They are supposed to shield from outside interference. Push down, turn 1/4 turn maybe to the left and they slide right off.

Then take the eraser end of a pencil and nudge/tap/push on them one at a time. Make sure your guitar is unplugged but the amp is cranked up. If you hear that 'tapping' coming through your speaker, then there is a good chance that tube is overly microphonic.

Replace it.


I've had this experience before and an OD pedal just exasperates the problem.

It could be a bad connection in OD pedal, faulty cable, faulty jacks, etc too.
Last edited by 311ZOSOVHJH at Sep 12, 2009,
#5
Okay I'll take a quick look at that in a minute just a few questions before I do.
Just to make sure I have the right tubes there will be less preamp tubes than power amp tubes right?
If I do have to replace them do I have to replace the whole set?
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#6
I'm not sure exactly which 900 you have but my amp is similar and came with 4 EL34 power tubes and 4 smaller preamp tubes. Once you take the back off ( I leave mine off all the time as well) it should be apparent. Is this a combo or head? 50w or 100w?

Either way, you should be able to see the aluminum cylinders I was talking about. The power tubes are much bigger and will be closer the the power transformer which is a big metal box.

And no, you don't have to replace all the preamp tubes - just the one that is microphonic.
#7
Quote by 311ZOSOVHJH
Don't know if it is the OD or not but are your sure you do not have a microphonic preamp tube? Just askin'


I would';ve thought microphonic pickups were more likely - Epiphones seem to be particularly bad for them.

Can you describe the feedback? Is it sudden, harsh and screechy? Do you still get it if you turn down the guitar's volume?
#8
It is sudden harsh and screechy yeah, I don't get it with the volume off either.
@311: It's the 100W combo, how do I get the casings off? I can't see any screws or anything.
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#9
Quote by SimplyBen
It is sudden harsh and screechy yeah, I don't get it with the volume off either.
@311: It's the 100W combo, how do I get the casings off? I can't see any screws or anything.


push the metal cover in and turn it to the side

not too hard though. it should come off really easily
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Quote by Dempsey68
get a cheap marshall... my MG15DFX has a button that simulates the sound of one of the expensive tube marshall amps.
#10
Here is a little tutorial I did for the Valveking thread if it helps. Don't mess with the screws at the base - just push down on casing and turn to the left like I said until the 'catch' releases. There is a spring on top of the casing that helps keep the preamp tube 'seated'.

https://www.ultimate-guitar.com/forum/showpost.php?p=16508706&postcount=7

Edit: lol turn LEFT not right

Preamp tube itself gets pulled strait out if you ever need to pull one. NEVER turn a preamp tube in it's socket or you will break or bend the pins.
Last edited by 311ZOSOVHJH at Sep 12, 2009,
#11
If I'm changing tubes, what preamp tube would give me a bit more headroom for cleans?

Also, thanks for the help 311 that tut is great
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#13
Not gonna lie, I was disappointed when I saw that you were trying to get rid of feedback as opposed to generating lots of it


Sometimes stacking too many OD's can cause very specific frequencies to feedback. I have that issue when boosting my Classic 50 with certain OD pedals.

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#14
Quote by SimplyBen
It is sudden harsh and screechy yeah, I don't get it with the volume off either.
@311: It's the 100W combo, how do I get the casings off? I can't see any screws or anything.

Don't waste your time with the preamp tubes until you've tried the same setup with another guitar! I'll bet you a fiver the pickups are microphonic, not the tubes....
#15
Quote by stradivari310
Not gonna lie, I was disappointed when I saw that you were trying to get rid of feedback as opposed to generating lots of it


Sometimes stacking too many OD's can cause very specific frequencies to feedback. I have that issue when boosting my Classic 50 with certain OD pedals.


Don't get me wrong, in the right place feedback is great. But this is just inconvenient feedback.

@kyle - I'm going to try both, the guitar first and then I'll check the tubes. If it is the pickups it gives me a good excuse to buy the BKP I've been looking at

@311 - It's the MK III 2101, a 1x12 combo.
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#16
Well preamp tubes are easy to check. I'm not sure how you trouble shoot a microphonic pup outside of taking guitar apart and using a multimeter - but I wouldn't even know what values to look for.

But yes, certainly you can:

try your guitar in a different amp
try a different guitar in your amp

(yeah OK, so put the back on when your done for better speaker response)
#17
It's my pickups I think, just tried my SG and it's fine. Is it just a case of replacing them?
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#18
Quote by SimplyBen
It's my pickups I think, just tried my SG and it's fine. Is it just a case of replacing them?


Maybe you could pot them?
#20
Ben - do you have a multimeter?

If not, get one. They are $15 at RadioShack for example.

Then look up the resistance values for each pup. It could be a matter of a crossed wire or bad solder joint. I just got done going through this entire exercise myself. I wouldn't run out an buy new pickups just yet.

Set multimeter to 20k Ohms of resistance. Use the other end of guitar cable as test point for now. Plug other end into guitar obviously and turn volume all the way up. Here are my readings just to give you an example.

Neck: 7k
Mid: 7k
Bridge: 14k


Last edited by 311ZOSOVHJH at Sep 13, 2009,
#22
I'll try get my hands on one, seems they're pretty useful for guitar & stuff anyway so I might as well grab one.

It could well be the wiring which when I get the chance I'm going to redo anyway because it's not the greatest & is quite messy. Could the fact that I have a bare wire grounding my bridge be affecting it?
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#23
Quote by SimplyBen
^ Would that be worth the hassle? They're just epi stock p/ups

Not particularly difficult to do (I usually melt a few candles and some beeswax in a tin can, floating in a pan of hot water) but if you've got the money, and think the guitar's worth upgrading, I definitely recommend new p/ups.

Epiphone pickups aren't great - in fact, as soon as I saw you were using an Epi I guessed it would be microphonic pickups
Bare Knuckles will likely put your guitar tone on par with a good Gibson...they really are excellent.
Last edited by kyle62 at Sep 13, 2009,
#24
Quote by SimplyBen
I'll try get my hands on one, seems they're pretty useful for guitar & stuff anyway so I might as well grab one.

It could well be the wiring which when I get the chance I'm going to redo anyway because it's not the greatest & is quite messy. Could the fact that I have a bare wire grounding my bridge be affecting it?

not sure, most of the ones i've seen are grounded so....