#1
I've got an Ashdown Electric Blue 130 amp (the old one), and ever since I got it (used) it will crackle when moved or tapped. So I took the amp out of the cabinet, and narrowed down the issue to the two largest capacitors on the circuit board. The solder joints look good, so I believe one or both are damaged inside. The caps say Dubilier 4700uf(m) 100v 85*C and have part numbers L9736 and L9732 if that helps. I've googled those specs, and it came up with little. My knowledge of technical electronics is small, so my question is, can you educate me on capacitors, and help me find a replacement? For example, can I go with a higher capacitance or will it damage the amp? Also do you know where I can find a suitable replacement? Any help on this will be greatly appreciated.

Also, I have the schematics from Ashdown if that helps.
live to jam and jam to live
#3
You probably have some loose pots.
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#5
Id measure the capacitance of those things before replacing them and see if they come close to your specs you put. Usually caps either work or don't. "Moved or tapped" that is defiantly a indicator something is loose, even the pots can affect it if they sound scratchy when you use them. I mean the whole damn thing vibrates when you play it.
Last edited by cruc1a7 at May 8, 2008,
#6
ok, here is why I think it is the caps. I took the head out, and set it on top of the amp. When tapped lightly, it pops and crackles. Now I checked every knob and button, wiggling and turning them. No popping or crackling. But just BARELY touching one of the big caps causes a nice sequence of loud pops and crackles, which can be regulated reliably by pressure (i.e. touch it, it crackles, let go it stops). I have to tap the amp harder in other places to get it to pop, which is enough to make the cap move a bit. I took out the main circuit board (not the preamp board), and every connection looks good, including the capacitor connections. Now, the suspect cap feels a bit loose, even though the solder underneath is secure. The wax that is supposed to secure it has long since broken, which has allowed it to move. From what I know of capacitors, this tells me that the wire has become loose inside the black cylinder, and is making a bad connection inside.

Also, keep in mind that this is with no bass or instrument cable connected.

cruc1a7 or anybody who can answer this: how can I measure the capacitance?
live to jam and jam to live
#7
You need a digital multimeter. My Fluke has cap symbol on it like you would see on a schematic.
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#8
Sounds like a ground issue to me. +1 to tightening the pots, jacks, and switches. Just a friendly reminder that there is deadly voltages in amps, even when turned off. The caps will store voltage until the are bled off.
#9
Quote by barefootboy
Just a friendly reminder that there is deadly voltages in amps, even when turned off. The caps will store voltage until the are bled off.


^ Also this
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#10
Do you have a link to the schematic? (I'm lazy this morning.) You might be on the right track with your theory. Digi-Key has a few: http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=131081;keywords=capacitor

With that high of a value, I'm thinking your amp doesn't have a tube rectifier. In that case, a higher value won't be detrimental, as long as the voltage rating meets or exceeds the original.
#11
Sounds like you've got it narrowed down pretty well. If you email or post a link to the schematic I can help you figure out what you can replace them with.
I would like to point out as some other people have that the worst thing you could possibly be doing with your amp is opening it up and poking the filter caps. Take some time to look up proper safety procedures (discharge, one hand in the pocket, etc) for working with tube amps.
#12
have the top of the caps popped up, or are they flat?
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#13
The top of the caps are slightly convex, how far popped up is "popped up"?

to everyone who wants a copy of the schematics: I have it on my comp. PM me your e-mail and I will send it to you.
live to jam and jam to live
#14
That's a sure sign that they are bad

If they're popped up at all, even slightly, they will still cause problems

Replace those caps
Call me Dan

Gear:
2015 Les Paul Studio - Wine Red
Ibanez SA120 (black)
Marshall MG100HDFX
Custom Les Paul (work in progress)
About 10 other guitars and a big pedalboard. lol
#15