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Right, so I've had this old Peavey Century 200 (4ohm) head sitting around for AGES, finally the other day I decided to give it some company by purchasing a TC Electronic 2x10 (8ohm) cab.

Because the Peavy is 6,000 years old and the cab is pretty modern, they both have different connection plugs (Peavey is standard 6.5mm jack output while the cab is Speakon input).

So I buy the right cable to connect them, turn on the power and everything seems ok. A short while later however I start getting this almighty thudding sound, like a heartbeat on steroids. It doesn't matter which dials I turn on the amp, even with everything dialled off, I still get the thudding sound. I look at the speakers and they're about to jump out of the cab.

Here's the weird part though, when I tilt the head 45 degrees, the thudding stops completely and everything functions as it should. I should also mention there is quite a lot of heat, I'm sensing this is a bad thing as I've never had an amp kick out so much heat.

I'm hoping someone can help me understand what's going on before I ultimately burn down my house.

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Sounds scary! :/

I'm sure someone on here will be around soon who'll be able to work out what's happening.

Good luck!

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Get the amp looked at by an electronics tech pronto. Speaker cone displacement like that sounds like a DC fault on the amp output.

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17 minutes ago, nilebodgers said:

Get the amp looked at by an electronics tech pronto. Speaker cone displacement like that sounds like a DC fault on the amp output.

I was hoping to take the amp apart tonight and have a look inside. I believe it's a solid state amp, otherwise I'd assume it was one of the tubes playing up.

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I'm guessing that a power supply cap solder joint has come loose. When the amp is sitting normally the cap is out of circuit, when tilted it's in circuit. I'd re-solder those, then test the power rails to be sure there's no pulsing of the DC. Be aware that the caps will store a considerable charge, so if you don't know what you're doing don't mess with it.

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My first question would be what experience do you have servicing solid state electronics. Just 'cos you've owned the amp for ages doesn't mean that you can play fast and loose inside the amp. in general doing so just causes more damage than already exists. Do you even have a clue what to look for?

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10 hours ago, BassmanPaul said:

My first question would be what experience do you have servicing solid state electronics. Just 'cos you've owned the amp for ages doesn't mean that you can play fast and loose inside the amp. in general doing so just causes more damage than already exists. Do you even have a clue what to look for?

I have basic knowledge of amps, I'm more of a guitar tech. But a good buddy of mine services and repairs his own amps, both SS and tube, so I'm sure between us we can fix the issue. I understand that as long as the amp has been powered down correctly there shouldn't be too much in the way of carefully diagnosing the problem.

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18 hours ago, Bill Fitzmaurice said:

I'm guessing that a power supply cap solder joint has come loose. When the amp is sitting normally the cap is out of circuit, when tilted it's in circuit. I'd re-solder those, then test the power rails to be sure there's no pulsing of the DC. Be aware that the caps will store a considerable charge, so if you don't know what you're doing don't mess with it.

Exactly my first thought, power supply caps. The other thing to look for is leakage from them any sticky goo is terminal and they need to be replaced.

Second thought is the same too. Electric shocks from the caps are DC not AC and believe me are worse to experience than mains shocks. They can stop your heart so really, really be careful and if you have any doubts leave it to someone who has more knowledge.

 

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4 hours ago, r_vw52 said:

 I understand that as long as the amp has been powered down correctly there shouldn't be too much in the way of carefully diagnosing the problem.

Do you know how to drain the power supply caps and why you have to?

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1 hour ago, Bill Fitzmaurice said:

Do you know how to drain the power supply caps and why you have to?

As I said, a good buddy of mine is very clued up on this sort of thing, so I'll be handing it over to him and learning as he goes. I really only wanted to know what was causing the problem in the first place so I had something to go on. I didn't want to just hand over a faulty amp (to him or to a tech) and not have a clue about what the problem could be.

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On 19/01/2021 at 03:30, r_vw52 said:

I have basic knowledge of amps, I'm more of a guitar tech. But a good buddy of mine services and repairs his own amps, both SS and tube, so I'm sure between us we can fix the issue. I understand that as long as the amp has been powered down correctly there shouldn't be too much in the way of carefully diagnosing the problem.

Well good luck with that then. I hope you get the amp fixed. :)

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The name of that  phenomenon , what you discribed as "thudding noise" is called :  "motorboating".

"Motorboating" is in fact a low frequency feedback ,...and in this case , it will be caused  due to a lack of capacity of one ( or both ) filter capacitors , located in the the power-supply section of the amp .

So , mister Bill Fitzmaurice was right ! ,....it's just a simple faillure , and it's very easy to fix :

Just re-solder the solder-joints of these capacitors , ...and your amp-problem will be solved ! 😉👍

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I just posted a new topic as I have a Peavey T-Max which sounds like it's having similar issues, although I've never tilted the amp to try and make it stop....hmmnn.

Did you get sorted with this in the end?

 

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On 19/01/2021 at 14:49, r_vw52 said:

As I said, a good buddy of mine is very clued up on this sort of thing, so I'll be handing it over to him and learning as he goes. I really only wanted to know what was causing the problem in the first place so I had something to go on. I didn't want to just hand over a faulty amp (to him or to a tech) and not have a clue about what the problem could be.

I'm guessing / hoping that your friend has access to a snuffer stick to safely drain the capacitors. In my childhood I saw a friend of my dad's make a mistake with a capacitor in a (1960's) television which he was fortunate to survive, though I guess this would be extreme by comparison to the amplifier versions.

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Dont capacitors discharge on their own over a couple of days, or do they store their charge for eons ?

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16 hours ago, fleabag said:

Dont capacitors discharge on their own over a couple of days, or do they store their charge for eons ?

To some extent true, I'm sure @agedhorse could give us some definitive info. There is the potential (geddit 😆) of a residual charge hanging in there and any sort of DC shock is emphatically life threatening. Valve amps more so than solid state but even so. I purchased a snuffer stick and discovered where to use it before I even cleared the dust out of my TE Ah500x. This had the additional benefit of me being able to do a visual check on the state of the Capacitors. Roll on to when my friends and I can go to the pals Dutch Barn and go for the full Spinal Tap option. 😂😂🙏🙏🙏

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Caps tend to keep some of the charge in them. If you want to be on the safe side, use a big resistor and, well, if you knew this, you know what to do.

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If there are no bleeders designed into the circuit, or if there is a failure with the bleeder circuit, caps can store charge for a surprisingly long time if there's no load (like a typical plate circuit).

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