Black Smoke: Not good

[Modular1]

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?

[Transcend]

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.

[Twinfan]

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?

[jpfamps]

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

[Modular1]

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....

[Twinfan]

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...

[Modular1]

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.

[Dmoney]

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.

[jpfamps]

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.

[jpfamps]

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).

[Modular1]

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.

[shobet]

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.

[Modular1]

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? :/

[Modular1]

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:

[Transcend]

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