Bare Knuckle Pickups Forum
Forum Ringside => Tech => Topic started by: Modular1 on May 31, 2011, 06:34:53 PM
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Hey Guys.
Just got home and decided to have a blast on my little fender champion 600. Had it on full volume with a fuzz pedal and my Holy Diver driving it really hard. Suddenly the sound cut out and black smoke started pouring out of the back of it. This is the first ever tube amp i've owned so I'm thinking ive probably blown the tube in it.
Im an electrician by trade so I'm sure I can probably repair it myself but I thought I'd check in with you lot on any advice before i start meddling around inside it.
From left to right im thinking we have the power transformer, the tube, another transformer (?), and a mysterious metal pillar (cover?) which looks like it might have a spring and another tube in it. The smoke looked like it was coming from the transformer end but it never blew any fuses and the power light remained on.
im not really familiar with this old tube electrics and i know they are dangerous even when unplugged, but im not sure what to avoid doing.
As you can see in the photo, the tube doesn't look like its been burning. Do they go black inside when they blow?
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What you need to do is avoid the filter caps inside the amp they can hold lethal charges unless bled.
If you can open it up and just take a photo before poking around and upload it here we may be able to spot something for you and mention where all the danger is.
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Black smoke? Sounds like it was possessed by a demon! :o [Sorry, been watching Supernatural this evening :lol:]
The tube under the cover is the preamp ECC83/12AX7. Smoke usually equals a blown capacitor or transformer?
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Most likely it will be a resistor and should be easy to fix.
The best candidates are:
R11, R26 and R10.
These may have blown because the output valve shorted, so could have simply blown due to being slightly under rated.
It will be very obvious which resistor/ have expired.
I would replace these with the highest rated part you can fit in the space. This will be at least 3W, but a 5W part might also fit.
Increasing the value of R26 to say 1k will improve reliability, especially if you are thrashing the amp.
You can get the schematic from the Fender website here:
http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf
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I powered it back on when i had the back cover off to see if if the fault was visable. what i saw was a green flame from the circuit board. ive opened it up to have a closer look and it appears some resistors have fried. Don't know if this is a symptom or the root of the problem. Perhaps one of them caught fire and damaged the other two. Why did they catch fire in the first place?
Gremlins?
This might be a job for Sam and Dean after all....
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I'm no expert, but resistors can blow if a valve pops. You may find your 6V6 has gone down to hell with all the other tortured souls...
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JPF. Thanks! Your post beat me to it. So its likely that one of the tubes has packed up and the resistor damage is a symptom of that. Would the offending tube look like its damaged? The big clear one still looks clear and unburned.
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out of the two the big one is the less reliable and uses more juice. it can look totally fine but be arcing or shorted inside. I'd avoid turning your amp on at all until its sorted from now on. don't fire it up with no big power value in it.
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OK, R10 is the cathode resistor.
This is likely to have blown due to the power valve shorting out. A further consequence of the power valve shorting is that the HT can be imposed on the filament supply.
R15/16 are resistors which reference the filament to ground (to reduce hum). They were not design to withstand large voltages and when the valve shorted to the filament these were smoked too.
Replace R10 with a higher rated part, and replace R15 and R16 with 0.6W 100 ohm MF resistors.
I wouldn't trust your output valve, so I would bin it and get a new one.
Also check R26 and R11, and increase the value of R26 if you are thrashing the amp.
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JPF. Thanks! Your post beat me to it. So its likely that one of the tubes has packed up and the resistor damage is a symptom of that. Would the offending tube look like its damaged? The big clear one still looks clear and unburned.
You're unlikely to see any damage to the power valve.
However if you have a multimeter you might be able to detect a short between the filament (pin 2 or 7) and the plate (pin3) or screen (pin 4).
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i cant see r10 on the diagram. r15= 100ohm resistor? r16= 100ohm resistor?
I dont really deal with electronics in my trade so im a bit clueless of the replacements to buy, though im quite happy soldering them in. Could you possibly give me some links to the parts on RS/maplin or something? It would be much appreciated.
I was thinking of doing some upgrades on this amp anyway so this has spurred me on. I wanna get new tubes (both) and a new speaker.
Any upgrade suggestions? I'd like it to have a nice dirty sound that breaks up at lower levels if thats possible. I'm going to replace the speaker and grill material too.
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It's a nice cheap amp to upgrade bits and pieces on. I swapped out the speaker in mine for a Jensen unit. Upgrading the calves is a simple improvement as well.
I think you change or even remove some of its innards to give it more gain I think. There are plenty of sites detailing mods for this amp, google is your friend.
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I swapped out the speaker in mine for a Jensen unit. Upgrading the calves is a simple improvement as well.
Where did you buy the jensen?
calves? :/
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http://www.watfordvalves.com/product_detail.asp?id=2709 i found this kit which sounds like just what im looking for.
but thats a bit pointless until i know what i need to do for the repair :|
...should i just buy that Tiny Terror Combo i've been gassing over? :crazy2:
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What you have there is a very easy fix.
When i get in from work i shall get you some part numbers from maplins.
But in all seriousness if you just search by the resistance value and wattage it will bring up what you need
eg. 100r 0.6w
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I might replace the other ones jpf mentioned too just to be on the safe side. Although all this has made me want to buy a new amp. Lol.
After looking at prices on the tiny terror I noticed Orange have announced the Dark Terror high gain version. I might just grab myself a cheap little Blackstar ht1 to keep me amped up until I can get a dark terror in the future (if they turn out to be any good!!)
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its a couple of quid at most to fix (if you already have a soldering iron) and a hundred plus for a new amp though?
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Don't get me wrong. I'm definitely going to fix it. But I've wanted to get a bigger more rock/metal amp as well. I've recently given my old solid state Marshall amp to my nephew so I left myself without a backup. If I have another amp it means I can take my time and turn this into a proper upgrade/mod project and not just a rushed repair.
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thats true. it give you a platform to tinker and learn on.
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I dont really deal with electronics in my trade so im a bit clueless of the replacements to buy, though im quite happy soldering them in. Could you possibly give me some links to the parts on RS/maplin or something? It would be much appreciated.
If you've got a Maplin near you, that's probably your best bet. You can check their stock online.
I use Rapid Electronics a lot. They are cheaper than Maplin, but mail order only, so I always make sure I oredr enough items to get free shipping (£35 I think).
If you get really stuck we've probably got all the parts you need in our workshop.
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Can I just be the first to say Well Done.
Dunno why no one has said it yet. :lol:
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yeah smoking an amp with a fuzz - even if it is a 5w champ - is a mark of great distinction!
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Can I just be the first to say Well Done.
Dunno why no one has said it yet. :lol:
:D
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I was thinking of popping into town to get the parts from maplin to repair this amp. Looking back on this thread I get the idea I need to upgrade as well as replace the R26 resistor along with the other fried ones.
Could you guys please help me complete this shopping list in foolproof way (lol) because I don't really understand the ratings of the parts i need to buy and the last thing I want to do is buy the wrong part.
R11= diagram says fr1k 2w (I have no idea what that means)
R15= 0.6W 100 ohm MF resistor
R16= 0.6W 100 ohm MF resistor
R26= diagram says fr470 2w (I have no idea what this means)
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Upgrading the calves is a simple improvement as well.
Moooooo!
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R11= diagram says fr1k 2w (I have no idea what that means)
i believe its just 1k 2/w heres a part from maplin
http://www.maplin.co.uk/metal-film-2w-resistor-5729
item D1k
R15= 0.6W 100 ohm MF resistor
http://www.maplin.co.uk/100andohm-to-300andohmmetal-film-0.6w-resistors-341564
Item M100R
R16= 0.6W 100 ohm MF resistor
http://www.maplin.co.uk/100andohm-to-300andohmmetal-film-0.6w-resistors-341564
Item M100R
R26= diagram says fr470 2w (I have no idea what this means)
http://www.maplin.co.uk/metal-film-2w-resistor-5729
ITEM D470R
id be tempted to try this too
http://www.maplin.co.uk/3-watt-wirewound-resistor-2173
Item W470R
Id wait until the first and last of these gets confirmed though as i arent 100% sure if the FR is significant
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Thanks. I don't know one type of resistor to another.
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FR stands for "fire resistant", although you will also see these described a "flame proof".
The 2W metal film resistors from Maplin will be fine.
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FR stands for "fire resistant", although you will also see these described a "flame proof".
The 2W metal film resistors from Maplin will be fine.
ahh that makes perfect sense now!
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Thanks guys. will see if i can pick these up from the shop in town today.
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Hopefully these are the right thing.
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I would be able to tell you if i wasnt colour blind....
I always use a multimeter for checking the values.
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yeah they all check out. i must say i'm making a right mess of the soldering though. :(
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just take it slow and make sure you tin the tip before and after each joint.
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Butchery. That's the only words that describe the mess I've made. I think it will work. :/
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Butchery. That's the only words that describe the mess I've made. I think it will work. :/
have you got a multimeter to check the connections?
Just so long as the connections themselves are good and you have continuity it should be fine.
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yeah, it connects. One of the tracks came away from the pcb board though. I had to link the next solder point on the same track with the long tail of one of the resistors. Rough. I suppose its just the same thing as a hand wired amp though lol.
Ive ordered a valve and speaker upgrade kit from watford. Hopefully it will be fine. If not I think it may get posted off to mr Jpfamps to see if it can be saved.
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Desoldering without damaging the board is much harder since the banning of leaded solder.
Unless I have a very good reason to, I never try to remove parts from a PCB intact: the parts are cheap, the board is expensive.
To remove parts from the PCB I snip the leads, melt the solder around the leads and carefully pull the lead through the hole. After this you can clean up the pads with some solder wick.
To make the job easier, you can add some leaded solder to the joint; leaded solder has a much lower melting point than lead-free.
These days you will also need a good soldering iron; a old 12W effort won' be able to heat the joint quick enough and you risk damaging the PCB, especially on boards with through plated holes.
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I thought it was because I used a 40w iron. I thought it might have been too hot. Will using the lead soldered to the next point along the damaged track be ok? I wrapped it round the stub of the lead that was the next point on the track and blobbed solder on it.
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Sounds like you done a sensible repair to the board.
With the best will in world PCBs don't take kindly to repeated cycles of soldering and desoldering.
Regarding your iron you are actually more likely to damage the board with a lower powered iron.
I've posted on this elsewhere, but to briefly recap, the key to good soldering/ desoldering is to heat up the joint as quickly as possible to the melting point of the solder, thus minimizing heat transferred to surrounding components/ PCB tracks.
All things being equal, a 40W iron doesn't reach a higher temperature than say a 12W iron, however a 40W iron can deliver more energy to the solder joint with cooling itself, so you can heat the solder joint more quickly, and hence reduce collateral damage.
The problem with lead-free solder is it's higher melting point, typically 227 deg C, but can be higher, cf around 180 degC for leaded solder.
The necessitates the use of a higher tip temperature; I use 430 degC forlead-free work cf 370 degC for leaded solder. Obviously this increases the chances of collateral damage somewhat, however trying to melt lead-free with an iron designed for leaded, and hence lower temp, increases the likely hood of collateral.
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Well the new valves and speaker arrived today. It works fine and sounds great so Im hoping it will hold together :)
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Well the new valves and speaker arrived today. It works fine and sounds great so Im hoping it will hold together :)
Good.
Im glad you got it sorted.
What speaker did you get and how is it?
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its the kit that somebody linked to on here. early break-up weber speaker. Thanks to everyone for your help on this. It would probably not have got done at all if not for you guys.