# Amp head blew again...please help?!



## canadiangeordie (Jan 10, 2009)

Happy Sunday!

A few weeks ago i snagged a used Hughes & Kettner Vortex head (SS) from Kijiji for $100. Played it through a 2x12 Behringer cab at the guys' house, liked it, bought it.

Took it to jam that Saturday, plugged it into my Hartke cab, turned it up and it died. The power light was on, but there was no sound at all and the channel/footswitch LED was off. Cam at Matt's Music (London) fixed it, here's what is on my receipt;
- Replaced Blown output Trans
- Replaced blown drivers trans
- Replaced blown 2A fuses
- Replaced burnt resistors
- Replaced defective 15v3a
- Replaced transistors
- Replaced drodes, 
- Replaced burnt traces, checked voltages.

Soo..quite an overhaul. Took 2 weeks and cost $110 but i was like a kid on Christmas morning when i picked it up yesterday, along with a new Randall 4x12 w/vintage 30's, and off to band practice i went. Hooked everything up and...it blew again. I literally tuned up, played an e5, and it went. This time there is no lights on at all, no sound at all. I opened it up, fuses are fine, nothing 'looks' blown but i am not am amp tech.

What could be the problem? Everything's just been fixed! Is it even worth putting any more money into it?!

Many thanks in advance!
Ryan


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## nonreverb (Sep 19, 2006)

Are you sure the wiring in the speaker cab is correct? Did you try a different speaker wire the second time around? Sounds like you might have a short in your cab somewhere....it's definitely worth checking.


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## canadiangeordie (Jan 10, 2009)

The speaker cab is brand new..and the connecting cable is the same one. Would the cab wiring cause the head to blow?


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## mrmatt1972 (Apr 3, 2008)

A Solid State amp does not need a speaker load to function. I.E., a short in the speaker cable is likely not the problem. No lights at all is probably a fuse. Check it yourself. It probably stems from bad wiring at the jamspace. Too much voltage or a fluctuation. Maybe a bad ground. Get a circuit tester for the plug itself. They're little yellow thingies that you can buy at any hardware store. They have various led light patters to indicate circuit problems.


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## canadiangeordie (Jan 10, 2009)

mrmatt1972 said:


> A Solid State amp does not need a speaker load to function. I.E., a short in the speaker cable is likely not the problem. No lights at all is probably a fuse. Check it yourself. It probably stems from bad wiring at the jamspace. Too much voltage or a fluctuation. Maybe a bad ground. Get a circuit tester for the plug itself. They're little yellow thingies that you can buy at any hardware store. They have various led light patters to indicate circuit problems.


Our jamspace is the drummer's basement...i've always had a 2X12 combo hooked up to an additional 4X12 cab up until recently, with no previous issues. Could be an impedence problem? Though the guys at Matt's assured me that everything was good to just plug in, and go. And after opening it up, the fuses in the head look perfect. Nothing else went off/out at the time either (the PA and my ISP Decimator are plugged into the same socket via a multi-plug).


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## mrmatt1972 (Apr 3, 2008)

well, since it's just back from the tech, bring it back. they should stand behind what they did. If not get rid of it.


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## ed2000 (Feb 16, 2007)

mrmatt1972 said:


> Get a circuit tester for the plug itself. They're little yellow thingies that you can buy at any hardware store. They have various led light patters to indicate circuit problems.


*This is a must have tool for every musician who plugs into various unknown electrical outlets , very easy to use*. I found a few badly wired electrical outlets in my house using this tester (about $8.)...my Traynor was pluged into a reversed polarity circuit.


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## canadiangeordie (Jan 10, 2009)

And if i was to find a dodgy outlet? What would it show on the tester and how would i fix it?


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## nonreverb (Sep 19, 2006)

Reverse polarity isn't going to do much...many tube amps have polarity switches on them to do just that...reverse polarity. If the ground and hot are reversed thats' another matter although if that were the case, someone would have discovered the problem shortly after doing the job! A power surge is one possibility and somekind of short on the output would be the other. They are pretty well the main causes of catastrophic failure in SS amps....unless the repairman missed something.


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## guitarman2 (Aug 25, 2006)

canadiangeordie said:


> Our jamspace is the drummer's basement...i've always had a 2X12 combo hooked up to an additional 4X12 cab up until recently, with no previous issues. Could be an impedence problem? Though the guys at Matt's assured me that everything was good to just plug in, and go. And after opening it up, the fuses in the head look perfect. Nothing else went off/out at the time either (the PA and my ISP Decimator are plugged into the same socket via a multi-plug).



I've blown many fuses that looked perfect yet were blown. The best thing to do is put in a known working fuse.


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## Wild Bill (May 3, 2006)

canadiangeordie said:


> t...i've always had a 2X12 combo hooked up to an additional 4X12 cab up until recently, with no previous issues. Could be an impedence problem? Though the guys at Matt's assured me that everything was good to just plug in, and go.


Absolutely it could be an impedance problem! If it is, it's NOT the tech's fault, it's YOURS!

While it is true that SS amps are perfectly happy with no load at all they can burn out very easily if the load is a short or just too low. Normally the amp is marked with some kind of warning, such as "MINIMUM 8 ohms". If you are warned about a minimum you should pay attention.

You see, solid state circuits normally don't have an optimum load, like a tube amp. They simply put out more and more power as the load gets lower. The designer will shoot for a safe amount of power at a certain minimum load. So your amp might be rated at "100 watts @8 ohms". If you run it at 16 ohms the amp will just put out less power and no harm will be done.

If you go below the minimum, such as if you plugged a 4 ohm cab into a SS amp with an 8 ohm minimum, it will try to put out 200 watts. Since the transistors and all the parts involved were only rated as safe for 100 watts, things start burning out very quickly!

What is the impedance of the two speaker loads you are plugging into the amp? An 8 ohm with a 4 ohm gives a total of about 3 ohms. Is there any warning on the back of your amp?


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## Fader (Mar 10, 2009)

It could be a dodgy speaker cable. Is it common to both incidents?


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## canadiangeordie (Jan 10, 2009)

Wild Bill said:


> Absolutely it could be an impedance problem! If it is, it's NOT the tech's fault, it's YOURS!
> 
> While it is true that SS amps are perfectly happy with no load at all they can burn out very easily if the load is a short or just too low. Normally the amp is marked with some kind of warning, such as "MINIMUM 8 ohms". If you are warned about a minimum you should pay attention.
> 
> ...


I'll check this when i get home and post back.

First the head was plugged into a Hartke cab, and blew. Everything listed at the beginning of the post was 'fixed'.

I then took the head home from the shop ,plugged into my new Randall 4X12, blew. This time no lights, LED's, feedback, nothing. Same speaker cable (should i change this?). This is the first head+cab i've ever owned, always been a combo guy, and in all honesty i'm a complete novice. What should i be looking for on the back of the head and the cab, and what should i be aware of/alerted to? 
Again, sorry for the very amateurish questions...i just want to be able to play through the damn thing! All this assistance is hugely appreciated.


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## keto (May 23, 2006)

Amp will be either 4, 8, or 16 ohms. Some have switchable multiple taps for any combination. Likewise, cab will be wired either 4, 8, or 16 ohms (rarely in both cases, 2 ohms). They have to/should match. Amp at 8 *will likely but not guaranteed* go into a 16 ohm cab, but the other way is more dangerous - cab should have the higher number if mismatching. In some cases, mismatching results in a good sound but some amps just won't take it.


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## canadiangeordie (Jan 10, 2009)

keto said:


> Amp will be either 4, 8, or 16 ohms. Some have switchable multiple taps for any combination. Likewise, cab will be wired either 4, 8, or 16 ohms (rarely in both cases, 2 ohms). They have to/should match. Amp at 8 *will likely but not guaranteed* go into a 16 ohm cab, but the other way is more dangerous - cab should have the higher number if mismatching. In some cases, mismatching results in a good sound but some amps just won't take it.


The head reads: Power 100W Min Imp. 4 OHM.

And the cab has 2 inputs, left and right. One is 4 ohm, the other says 4 ohm in the same place but also 8 ohm below (i assume this means you can use either?!) There is also a stereo/mono selector, which i was told to leave on mono.

Soooo...going by that it should (technically) be fine?


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## greco (Jul 15, 2007)

Fader said:


> It could be a dodgy speaker cable. Is it common to both incidents?


 Did you check the cable for a direct short? (as mentioned as a possible problem by Wild Bill)

Cheers

Dave


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## canadiangeordie (Jan 10, 2009)

greco said:


> Did you check the cable for a direct short? (as mentioned as a possible problem by Wild Bill)
> 
> Cheers
> 
> Dave


The cable works fine when hooked up from cab-2X12 combo...how would i check for a direct short? Again, sorry if i sound like an idiot!


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## greco (Jul 15, 2007)

canadiangeordie said:


> *The cable works fine when hooked up from cab-2X12 combo*...how would i check for a direct short? Again, sorry if i sound like an idiot!


Seems like the cable is likely fine. However, cables can be a pain as they can "make" and "break" connection depending on the position they are in. Do you have an electronics multimeter? If not, take the cable with you when you go to the tech and have it checked there. If yes, just check to be sure there is no continuity between the the tip and the sleeve of the 1/4 inch plug(s). Be sure move the cable around, especially near the plugs, while testing it. 

Cheers

Dave


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## Wild Bill (May 3, 2006)

canadiangeordie said:


> The head reads: Power 100W Min Imp. 4 OHM.
> 
> And the cab has 2 inputs, left and right. One is 4 ohm, the other says 4 ohm in the same place but also 8 ohm below (i assume this means you can use either?!) There is also a stereo/mono selector, which i was told to leave on mono.
> 
> Soooo...going by that it should (technically) be fine?


Yes, but...!

If you plugged in a 4 ohm cab then yes, you should have been ok. However, did you not say that you were running an extra cab? When you add cabs they are normally in parallel and the combined load is always lower. Two 4 ohm cabs run at the same time will combine to make a 2 ohm load! That puts you under the minimum.

Still, normally when SS amps blow from driving too small a load it takes a bit of time, like minutes or more. To instantly blow suggests something else may be wrong. That being said, a shorted cable or a too low load WILL blow the parts you had replaced!

This is a head scratcher for a tech. Somebody who knows his stuff is going to have to go over your amp AND speakers to make sure everything is kosher.


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## canadiangeordie (Jan 10, 2009)

There is only one 4X12 cab, sorry if i didnt make that clear. The cab is brand new, and the head blew firstly with the older cab, so i'd be surprised if it were that. But, i'll get everything back in this week. I literally have no idea now what it could be...hopefully it is a fuse or something straight-forward.


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## Fader (Mar 10, 2009)

Unscrew the connector covers on the speaker cable and have a real good look for loose copper strands that could short across from ring to tip.


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## Rodavision (Feb 26, 2010)

I don't mean to insult you but I just want to check are you using a speaker cable and not a patch or mic cable?


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## greco (Jul 15, 2007)

Rodavision said:


> I don't mean to insult you but I just want to check are you using a speaker cable and not a patch or mic cable?


Good point....


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## canadiangeordie (Jan 10, 2009)

greco said:


> Good point....


lol no problem. I assume it is, it doesn't look like a patch or mic cable, and was given to me at Matt's Music for free when i told them i didn't have one. Like i said, i've used it many times hooking the cab to my 2X12 combo, without issue.


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## Bevo (Nov 24, 2006)

Did he replace the parts with the exact parts, maybe the original parts that first blew were not the originals. 
Have seen it in the HVAC world where a part out of the truck gets you by even though its wrong..


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## canadiangeordie (Jan 10, 2009)

Well...

Cam at Matt's said it's the worst put-together head he's even opened up. 100W, but with only a 1 amp fuse in the power input, hence why it keeps blowing. He reckoned i could even go through a fuse per night/gig if it's cranked as much as half way. I

Sooo......snagged a Randall V-Max for $300 plus my Redline 1. Pleased.


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