Burning Smell?

It wasn't me! · 18-07-2006 12:26pm #1

Okay, title kinda sums up the issue. Was playing through the new JCM800 (she arrived about half an hour ago) and after a few minutes noticed a burning smell from the amp. Was kinda worried, so turned it off, now I'm a tad worried there might be a problem with my new baby. It was fairly well cranked, so might this have caused it, I'm a tad perturbed, as I say. The tubes are a pair of 6550's, incidentally.

Also, all the tubes are somewhat blackened. no real experience of valve amps to date, but a problem to deal with right away sounds like an opportunity to learn something.

John · 18-07-2006 1:04pm

Are you sure it was from the amp? Are you using a speaker cable or a guitar cable between the head and the cab? Dabhoys had a similar burning smell when he cranked his Mesa and was using a guitar cable between the head and cab.

Kenny_D · 18-07-2006 1:32pm

If the tubes are old and have been pushed a lot they can crack or weaken. If they're the original tubes then you prob just need some new tubes. And like John said, use a speaker cable if you're not already doing so

It wasn't me! · 18-07-2006 1:39pm

John2 wrote:

Are you sure it was from the amp? Are you using a speaker cable or a guitar cable between the head and the cab? Dabhoys had a similar burning smell when he cranked his Mesa and was using a guitar cable between the head and cab.

It's a combo. Definitley amp-related, and given the amp is 23 years old, I doubt they're the original tubes.

It's the smell of burning plastic or blown bulb anyway, if it helps.

John · 18-07-2006 2:31pm

Ah right, beyond my "expertise" I'm afraid!

It wasn't me! · 18-07-2006 2:35pm

no worries. It turned out to be a non-problem. I gave the brother the task of putting the tubes in while I sorted the documentation, assuming he couldn't possibly get it wrong, and, well, he didn't quite put in one of the ECC83's, resulting in it falling out in my hand when I removed its casing, him receiving a glare, and the amp being easily fixed, with no current perceptible burning smell, and the tube filaments glow with a nice red hue, so we're sorted kiddies.

She sounds like an absolute monster, for those who care.

John · 18-07-2006 2:39pm

*cough* pictures *cough*

Karl Hungus · 18-07-2006 3:10pm

Yes, pics, and soundclips.

Creamy Goodness · 18-07-2006 3:48pm

Ban Him...

Pyr0 · 18-07-2006 4:01pm

Yeah three posts without a pic, he's asking for it now...

Eoin Madsen · 18-07-2006 6:07pm

It wasn't me! wrote:

no worries. It turned out to be a non-problem. I gave the brother the task of putting the tubes in while I sorted the documentation, assuming he couldn't possibly get it wrong, and, well, he didn't quite put in one of the ECC83's, resulting in it falling out in my hand when I removed its casing, him receiving a glare, and the amp being easily fixed, with no current perceptible burning smell, and the tube filaments glow with a nice red hue, so we're sorted kiddies. She sounds like an absolute monster, for those who care.

Hmm, I can't think of a reason why a loose valve would cause a burning smell. If the pins on one of the ECC83s weren't making contact, the amp wouldn't work at all.

When you say nice red hue... you mean a nice yellow hue, right?

Did you get the valves with it, or buy new ones yourself? If the 6550s are bit old, it might explain the burning odour. It also wouldn't hurt to clean out the amp, if you haven't already.

It wasn't me! · 18-07-2006 6:26pm

Well, the smell disappeared when I put the ECC83 in properly, and no, it was a red glow from the filaments in the 6550's. They are a bit old though, will replace them in time, but have no idea how to go about cleaning an amp out, and no desire to **** with it.

Eoin Madsen · 18-07-2006 9:56pm

Hmm, red does not sound right at all tbh. The filaments should be yellowish orange under pretty much all circumstances, afaik. Maybe we just have different ideas about where orange ends and red begins.

If the idle current is too high there is sometimes a reddish tinge to the plate. This would be a bad thing also, but quite correctable.

As for replacing teh valves... Valves don't really fail in a reliable or predictable way. Sometimes they blow out and short, usually taking out a fuse, occasionally burning out a screen resistor, and - just once in a while - blowing the output transformer. For that reason they're generally replaced at the first sign of something amiss. I would say blackened valves alone, even ignoring the smell of burning, would be cause enough to replace them without delay.

Just clean the inside around the valves with a cloth. I can only imagine what happens to all the dust and greasy fudge when it starts to heat up.

No need to go inside the actual amp, it's probably fine in there, and not safe to go poking besides.

It wasn't me! · 18-07-2006 10:08pm

I e-mailed Eurotubes asking for advice and requesting prices for a full retube, so we shall see what they say. I'd rather not get rode, given my current funding consists of six euro...

david · 18-07-2006 10:56pm

You'll get a retube from bob for about €55 shipped, i did

It wasn't me! · 18-07-2006 11:04pm

What did you get? I'm thinking KT88's instead of the 6550's anyway, but he'll advise best on that I imagine. How long were you waiting for an e-mail from him?

david · 19-07-2006 12:32pm

I just got a straight swap for whatever was in the ENGL, premium graded matched JJ's. Took about 30mins for the email reply, on a sunday

Eoin Madsen · 19-07-2006 1:28pm

You can always replace the ECC83s when you have the money, the power valves would be the priority anyway. It's hard not to get rode if you're shopping for KT88s though. Email watfordvalves.com as well and get a second opinion, and another quote. It's always good to shop around.

Don't forget, the amp will need to be re-biased.

It wasn't me! · 19-07-2006 1:29pm

I e-mailed yesterday, and no response so far, so we shall see.

It wasn't me! · 19-07-2006 1:31pm

I also asked about re-biasing, apparently it's simple enough to do myself, but I'm going to make sure I know what I'm doing beforehand. I've heard KT88's sound amazing in older Marshalls, any opinions around here? I assume there's no need to consider changing out the ECC83's anyway?

Eoin Madsen · 19-07-2006 1:37pm

Well, the Marshall "sound" really comes from EL34s. KT88s have more clean headroom, and are supposed to sound more linear. I have yet to try some myself.

Yeah, biasing is simple enough if you have a multimeter and a bias probe. If you don't have a bias probe you'll need some 1 ohm resistors and a soldering iron.

noh showband · 21-07-2006 12:56pm

Eoin Madsen wrote:

I can only imagine what happens to all the dust and greasy fudge when it starts to heat up.

The gunge heats up and you get a burning smell. Which is where we came in ...

It wasn't me! · 21-07-2006 1:13pm

Eoin Madsen wrote:

Well, the Marshall "sound" really comes from EL34s. KT88s have more clean headroom, and are supposed to sound more linear. I have yet to try some myself.

Yeah, biasing is simple enough if you have a multimeter and a bias probe. If you don't have a bias probe you'll need some 1 ohm resistors and a soldering iron.

I had heard the KT88's were a little angrier sounding, which is what I would be looking for. Where would I acquire those tools?

Eoin Madsen · 22-07-2006 1:32pm

Hmm, the consensus on KT88s seems to be the opposite in my experience.

Eoin Madsen · 23-07-2006 5:38pm

It wasn't me! wrote:

Where would I acquire those tools?

Go a-googling. If you have none of those things I would suggest something like the Weber Bias Rite.

http://www.amp-head.com/ also has all of the tools required. If you're getting a multimeter, don't skimp anyway. The cheap ones just won't have the accuracy. And I would strongly recommend the plate voltage probe as well, unless you feel pretty confident in holding the multimeter probes while measuring it. Plate voltage is usually around 400-500 volts.

punchdrunk · 24-07-2006 10:39pm

i believe the kt88 myth in part,came from people hearing about billy corgan's marshall head which was modded for kt88's,thing is he used them and the low input with these valves to get a cleaner sound so his big muff would sound clearer,basically with the pumpkins it was all pedal/preamp distortion not power amp,hence the valve swap

Eoin Madsen · 25-07-2006 9:06am

That sounds plausible. The Pumkpins sound was always preamp distortion.

Should probably add, while "modding" has been brought up, that putting KT88s into a JCM800 or 1959 does usually require that the bias resistor be changed to the get the bias into range.

It wasn't me! · 25-07-2006 12:05pm

am I best sticking with standard 6550's then? I imagine it'd be cheaper.

Eoin Madsen · 25-07-2006 12:46pm

I'd switch to EL34s.

It wasn't me! · 25-07-2006 12:53pm

EL34's are lighter though, are they not? I'm looking for a deeper, heavier tone.

Eoin Madsen · 25-07-2006 1:23pm

Define "heavier"? Afaik, 6550 has a slightly higher gain factor, which means they have more clean headroom - they will distort less at the same volume as an EL34. For this reason, 6550s are more commonly used in bass amps than EL34s. EL34 is the valve that a JCM800 or Super Lead was designed to use. To be honest, it's less relevent in a JCM800 than it is in a Super Lead - for the most part you're probably not getting close to distorting the powerstage unless your master volume is at 10 anyway.

6550s originally appeared in Marshalls when 1959s were first exported to the US. The amps were shipped without valves, and 6550s were a cheaper domestic US alternative. Most US players later modded their amps back to EL34 spec.

"Deeper" I can only imagine is a reference to it having an extended bass frequency response. I haven't heard much of this about 6550s. I know KT66s and KT88 definitely do, but, to be entirely honest, your cab is the bottleneck in the low frequency response of your rig anyway. You'd have to put in some 15s or get a larger enclosure before you'd start really noticing the difference.

EL34 are where you should start anyway, imo. Until you've heard them with your ears, I wouldn't put too much into anything anyone tells you. They define the "British" rock sound, and most people would consider them more aggressive sounding than most other valves given that they're less "mid-scooped". But, more to the point, they're what the amp was designed for - so start at the beginning.

Just my take on it.

It wasn't me! · 25-07-2006 2:06pm

Okay, thanks for teh help. I just hope a pair of EL34's won't set me back too far.

Yay! $24 for a matched pair from Eurotubes.

Still have to get the gear for biasing it though...

Eoin Madsen · 25-07-2006 3:02pm

Whereabouts do you live? If you're not pushed about getting into the biasing thing, it might work out as cheap to get someone to do it for you.

It wasn't me! · 25-07-2006 3:29pm

West Wicklow. I could get it done in Dublin I suppose, spend a lot of time in town, since I'm on a busroute, but the hassle of carting the fecker about would be unreal. How much will it cost overall to get all teh necessary gear? It'd probably be a worthwhile investment, but I'm kinda bankrupt, and probably cost a good chunk to get biased by anyone in Dublin either. Bit of a dead-ender. : /

Burning Smell?

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