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Post by mrdes on Oct 5, 2016 19:25:27 GMT
Dont know off hand but it could be capacitors or the amp chip over heating. Do you have an infra red th hermometer? If you do open up the amp and see if any part of the circuit is getting very hot. Dont touch anything whilst its open and powered on. If you arnt the dare devil type that likes playing with high voltage maybe bring it to a repair shop to see if they can give you a quote to fix it.
I have a marshall valvestate thats a bit noisy and reckon it needs a bit of tlc but as I bought it to crank up to 11 I havent bothered.....
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Post by mrdes on Oct 6, 2016 7:15:22 GMT
Dry joint could indeed cause the rumbly crackle especially if it was was a ground wire that had the dry joint. After reading this thread I got inspired to pull apart my old marshall and brandish my soldering iron but no difference although the ground wire to the chassis fell off as the crimp disintegrated. I may need a new tube as its a constant hum im suffering with. If your hunting down dry joints a magnifying glass can be very helpful. Hope you get it sorted.
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Post by iqvistus on Oct 6, 2016 7:28:27 GMT
My guess is the same as mrdes, bad caps or chip is running to hot. New thermal paste on the chip/chips/fets can do wonders sometimes Bad solder joints can cause all kinds of havoc btw, is the rumble 50hz mains hum or really low frequency? If it's mains hum it could be a bad solder joint somewhere in the grounding chain, bad shielding or it could even be mechanical vibration from the transformer. Edit: i was second on that
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Post by iqvistus on Oct 6, 2016 7:35:25 GMT
Dry joint could indeed cause the rumbly crackle especially if it was was a ground wire that had the dry joint. After reading this thread I got inspired to pull apart my old marshall and brandish my soldering iron but no difference although the ground wire to the chassis fell off as the crimp disintegrated. I may need a new tube as its a constant hum im suffering with. If your hunting down dry joints a magnifying glass can be very helpful. Hope you get it sorted. With regards to your problem, it could just be that the tube picks up interference. On my tube phono stage in my hi-fi I have metal shields over the tubes, with certain tubes they are not needed...but on others, like my nos RCA clear tops it's a necessity. Could be a simple cheap fix for you
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DefJef
THBC Moderator
Due to musical differences I've decided I can't work with myself any more.
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Post by DefJef on Oct 6, 2016 8:00:32 GMT
Thanks for your thoughts guys. Glad to hear my rumbly crackle inspired you to head for your soldering iron mrdes , even if it did lead to the general disintegration of your Marshall Definitely not mains hum as I recognise it iqvistus . That always sounds a bit like a fridge running to me. It's more of a lower static rumble with no hiss or hum to it at all. More like a stampede of buffalo in the distance but approaching slowly. Thankfully they never arrive! No tubes in this amp either. It's 130 watts of solid state. A Peavey KB300 which sadly means 3 inputs to trace. Incidentally the reverb pan in this doesn't work either. A connected issue? I wouldn't have thought so. Perhaps I'll get the magnifying glass out first and take a butchers for a dry joint. If it is the caps however, I believe these are where the fatal voltages are stored aren't they? Here's the beast: And here's it's rumply insides:
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Post by iqvistus on Oct 6, 2016 8:06:44 GMT
Ahh when the reverb don't work I would definitely think that they are connected, check for broken wires or obviously bad/loose solder joints...if non is present it's time to get out the multimeter Edit: Ohh, forgot to add: it could be that one of the transistors are bad
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DefJef
THBC Moderator
Due to musical differences I've decided I can't work with myself any more.
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Post by DefJef on Oct 6, 2016 8:14:30 GMT
Ahh when the reverb don't work I would definitely think that they are connected, check for broken wires or obviously bad/loose solder joints...if non is present it's time to get out the multimeter Edit: Ohh, forgot to add: it could be that one of the transistors are bad ARRRGGHHH! So many things! Where to start? I've had the reverb pan out and can't find a thing wrong with it so you may be right there. Thanks iqvistus, I'll multimeter away at the first opportunity.
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3,968 posts
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Post by salteedog on Oct 7, 2016 14:28:28 GMT
Impossible to say really without inspecting it. The only thing I can offer is that sometimes the effects loop on these old amps can be troublesome (although the symptom is usually a loss of volume not a rumble). You could place a patch cord between the send and return and see if it makes any difference.
Re. the reverb pan. I recently repaired one on the second hand Fender Stage 120se I bought recently. They are reasonably low tech as far as electronics are concerned. You need to check the continuity across send and return (lots of info on the web about this) and use a magnifying glass to find if there are any of the tiny wires broken. It took me two attempts to find the twp breakages in mine but I managed to repair it without much trouble. The thing now sounds bloody lovely too!
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325 posts
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Post by wildturkey on Oct 8, 2016 14:37:02 GMT
Check the solder joints first , on an old amp its usually Probably the best way to do it is to reflow all the joints so your not missing anything also do your pots and jacks Its very easy to do , just a tip an iron and a tiny bit of solderuntil you see the joint flowing , use a small tip Youll find plenty on youtube
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