Bare Knuckle Pickups Forum
Forum Ringside => Guitars, Amps and Effects => Topic started by: silentrage on December 09, 2008, 02:04:29 AM
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My amp just died today.
It played fine yesterday, but today when I flip it on... nothing. :/
I noticed that the pre-amp still works, but the power section is dead.
The power tubes don't light up.
F$%^$&@$%@%!!!!
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check fuses, sounds like one has blown
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what kind of amp is it? - seems odd that ALL the output stage valves have blown and the preamp valves are still fine.
fuses blow for a very good reason too, don't re-use the dead output stage valves.
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what kind of amp is it? - seems odd that ALL the output stage valves have blown and the preamp valves are still fine.
fuses blow for a very good reason too, don't re-use the dead output stage valves.
The fuse is fine, I checked with a multimeter.
The power amp section doesn't seem to be getting any voltage.
Is there a way I can check to see if the power amp tubes are dead?
They don't look burnt or anything from the outside, can I pull them out and test them with a multimeter?
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Is there an internal fuse for the power section? That may have blown?
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Is there an internal fuse for the power section? That may have blown?
I don't know, I took the amp out of the cab and had a look inside, doesn't seem to be an internal fuse in there.
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It would help if you were to say what amp it is
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It's a bugera 6262 212.
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anybody?
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I can't get much detail from the web on your amp.
However, if the pre-amp valves light up, but the power valves don't (double check this), then I would suspect that the filament supply to the power valves has expired.
This would normally be an unusual fault as the pre-amp and power amp in most amps use the the same supply, however it is increasing common for amps to run their preamp valves from a separate DC supply. If this is the case, then you could have LT failure to the power valves and not the pre-amp valves.
Can you check whether you get a signal from the pre-amp out? If you do then the HT supply is probably OK, and you are looking at a power amp LT problem.
The likely causes of this could be:
1) Broken connection/ cold solder joint in LT wiring.
2) LT winding on the transformer has failed.
Less likely:
3) Heaters to power valves wired in series, and one valve heater has gone open circuit. Can test this by using a multimeter to test continuity between pins 2 and 7.
VERY UNLIKELY
4) LT fuse has blown. (Most amps don't have an LT fuse, although this actually contravenes electrical safety regulations!!)
Incidentally are you using 6L6s or EL34s? EL34s have a greater LT current requirement and are more likely to cause faults 1 and 2 to manifest themselves.
Regardless, I suspect a trip to a competent tech is in order here.
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I can't see if the pre-amp tubes light up, they have a metal casing @_@
I get a good signal from the pre-amp out on clean channel though, and a very faint signal on the lead channel.
What's LT? Sorry I'm a tube nube. :(
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The metal casings twist and come off, then you can see the valves. Try that first and see if they're lit with the power on...
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OK, sounds like you need to take it to a tech.
The LT supply is the low voltage supply that heats the filaments in the valves in your amp. This is needed for them to conduct current. If this dies, your valves will not conduct current, and thus you will have no sound.
Its difficult to diagnose the problem with out seeing the amp, but my guess is that some part of the LT supply has died. This may power some of the valves in the preamp share LT with the power amp. THis is why the clean channel works OK but the distortion channel is very low output. My guess is that the first valve stage is common to both channels and runs of a separate LT supply (this is some that you can use a DC supply in the first few valve stages and thus reduce hum).
Regardless, I doubt you will be able to sort this out yourself.
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Thanks, that was very informative. :)
I'll take it to a tech and get it sorted out.
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Let us know how you get on — I'd like to know what the fault was!
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My guess is that the first valve stage is common to both channels and runs of a separate LT supply (this is some that you can use a DC supply in the first few valve stages and thus reduce hum).
sounds plausable, (like JPF said) if the preamp valves are getting voltage to the heaters but the output stage isn't, it could be that the output stage has AC heaters while the preamp from the PI onwards has DC heaters.
defo a job for a tech imo.
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Thanks! I was told by some bugera owners to just buy new tubes, but I dropped it off for repairs anyway just to make sure.
I'll call them on monday to find out what was the culprit. :)
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just trying to find a schematic for this thing - interestingly enough it appears to be a 5150+ clone.
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Yeah that's supposed to be exactly what it is.
I don't have the details anymore but I saw a post about how a guy who worked for peavey went to Bugera and started building these amps for them.
It may have a better clean section than the 5150+, although I'm not sure because I never had a 5150+.
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Amp's back after 2 business days from dropping it off, so I'll give them pluses for that.
The technician said the problem was a loose clip that caused a short, he didn't say if it caused a transformer to fail or an internal fuse to blow, but either way it was those damn clips that they used as a cheaper alternative to direct soldering on the pcb.
I'm gonna open it up and inspect it again before turning it on just to make sure.
Thanks for all the pointers and support on this one guys!
The moral of the story: if you buy a bugera amp, go in and finish the assembly before you use it. :/
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OK, sounds like the LT uses Molex (or even worse IDC!) connectors to run the LT between boards. This type of connection makes assembly quicker and often makes servicing easier, however they are prone to coming loose.
Both the LT and the HT present different problems for connectors — the LT conducts relatively high currents so needs to be low impedance, whereas the HT obviously has high voltages on it. I've seen problems with both.
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They look exactly like the power connectors in my PC, which I think are molex ones right?
Yeah I should've opened it up and checked it out first, might've saved myself some trouble.
It looks like the tech just super glued the problem connectors for the "fix", I knew it was too much to hope for them to solder it on.
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ribbon cable and push-on connectors have no place in an amp imo - soldered connections have worked in amps for decades with many of those amps still going strong. the only reason to change is cost.
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They look exactly like the power connectors in my PC, which I think are molex ones right?
Yeah I should've opened it up and checked it out first, might've saved myself some trouble.
It looks like the tech just super glued the problem connectors for the "fix", I knew it was too much to hope for them to solder it on.
Actually you can't really solder these connections very well (if at all), at best you get a botch which is just as prone to breaking — and it will take ages. Also hard wiring these connectors could cause servicing problems later down the line — ie you need to disconnect the Molex connectors to get the PCB out. My tactic now is to secure them with a dap of low-melt glue which can be removed at a later date.
My real bete noire is insulation disruption connectors (IDC). These rely on blades in the connection terminal to pierce the insulation of any wires inserted in them thus making the connection! As you can imagine these are prone to failure, and most Molex connectors are IDCs.......
A friend of mine used to roadie for several bands in the 80s who were using Akai samplers (yes I know the 80s were shocking). When these used to go down on the road he used to open them up an press at the Molex connectors in. This strategy was so successful one guy he worked for thought he was an Akai-trained engineer!
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Gotcha.
I think that's exactly what the service tech did to my amp, because now I see yellow blobs over a lot of the connectors that weren't there before. I guess they must be low melt glue.