Amp smokes but keeps playing

[artlaugher]

So I just finished recapping a 50's Challenger HF8 mono block hifi. I'd never turned it on before nor had the previous owner, so I don't know what condition the rest of it is in. I replaced all the caps (some values are not identical) and bought new tubes...

I didn't test the bias, I have no tools other than pliers and a soldering iron and I've never done this before; so I was pretty surprised when I turned it on this evening and it actually worked. The sound was a bit fuzzy and not as loud as I was hoping, but it worked perfectly. However after about 2 minutes of use smoke began seeping out of the chassis, even as the music kept playing just fine. I shut it down and looked around for the problem but couldn't see any visibly burned components.

I am surprise because I thought these things didn't smoke until AFTER something had broken!

I guess I need to take it to a professional, but does anyone here have any comments/idea??

Thanks

[Reeltarded]

Hypothet: current draw on transformer melted the jacket.

Describe the odor. What color was the smoke?

1. metal, you are not going to be happy. White cloud.

2. ozone, you are not going to be happy. White/Grey cloud.

3. plastic, you used underrated caps? Black sooty gooey yuckyuck.

These are but three options to consider from a great distance with limited information.

[alvarezh]

Recheck that the polarity of the caps you replaced are correct, they like to smoke if they are installed backwards. If correct, take the tubes off. Turn it on, if it smokes again turn it off and report from where you saw it coming out of.

That should make it easier for Miles to troubleshoot.

Ah, yes, very important, remember to drain those caps before you put your fingers inside the chassis, they could be charged with a couple hundred volts. Could kill you!

Post a schematic and get yourself a decent multimeter (didn't say you had one), for there will probably be more items to test.

All the best

[xtian]

Describe the odor. What color was the smoke?

Wow! a "You let the smoke out" F.A.Q.!

Awesome. Fill it out and we'll make it a sticky.

[Reeltarded]

That was pretty much it. I got it from the Lucas Electronics Field Manual 18th Edition. Mostly it explains what all the buttons in your British Leyland built car used to do. They make smoke replacement kits.

[vibratoking]

If it keeps smoking, it's gonna gain 30lbs.

[Reeltarded]

[Gaz]

You seriously don't have a multimeter? I don't even feel comfortable giving you advice if you don't know where potential lethal voltages are in your amp. You can get one for as cheap as $5.00. Hopefully you were just joking about the pliers...

[Colossal]

Smokin' tone? That's great!

[JazzGuitarGimp]

Smokin' tone? That's great!

Yup, fits right in with Weber's Smokin' Joe theme!

[artlaugher]

Thanks everyone for the advice,

Smoke was white, at this point I guess i'd be surprised if it wasn't the transformer, serves me right for just plugging the damn thing into the outlet. I'll pull out the tubes and place the amp in series with a desk lamp, we'll see if there's any smoke left...


fyi yes I do have a multi-meter, and YES I know where the dangerous voltages are, they are inside the amplifier!

[img:200:121]http://4.bp.blogspot.com/_Orni9qDxahM/S ... lander.png[/img]

[Tillydog]

Smoke was white

Hey! Another new pope!

White might be good news - treble check the polarity of your electrolytic caps. A common 'gottcha' seems to be installing the caps in the bias supply backwards (as they go + to ground)....

[tribi9]

and YES I know where the dangerous voltages are, they are inside the amplifier!

Hartman: Well ... no shit. What have we got here, a fucking comedian? Private Joker? I admire your honesty. Hell, I like you. You can come over to my house and fuck my sister.
[Sergeant Hartman smashes Joker in the stomach, sending Joker to his knees.] Hartman: You little scumbag! I've got your name! I've got your ass! You will not laugh! You will not cry! You will learn by the numbers and I will teach you! Now get up! Get on your feet! You had best unfuck yourself or I will unscrew your head and shit down your neck!
Joker: Sir, yes, sir!

[Colossal]

Hartman: Well ... no shit. What have we got here, a fucking comedian? Private Joker? I admire your honesty. Hell, I like you. You can come over to my house and fuck my sister.
[Sergeant Hartman smashes Joker in the stomach, sending Joker to his knees.] Hartman: You little scumbag! I've got your name! I've got your ass! You will not laugh! You will not cry! You will learn by the numbers and I will teach you! Now get up! Get on your feet! You had best unfuck yourself or I will unscrew your head and shit down your neck!
Joker: Sir, yes, sir!

R. Lee...sheer genius...

[artlaugher]

White might be good news - treble check the polarity of your electrolytic caps. A common 'gottcha' seems to be installing the caps in the bias supply backwards (as they go + to ground)....

Can somebody expand on the topic of bias supply? I've attached the schematic I'm working from. It does look like this is a cathode biased amp, but it says the caps still go negative to ground. that's how I wired them.

I turned it on again with no tubes, no smoke this time