amp smoking question:::

[sirDaniel]

So, my amp starts sounding a bit ... bad. So, I look in the back and a 6L6 is looking pretty toasty. Then the amp just quits, power jewel is out. So, RATS, I see I've been running a 8ohm load on the 4 ohm tap. CRAP. The actual 3A slo blo tripped. So....

should I think my powertubes are toast? or output tran? or??

Should I change the fuse and try again w/ a spare set o tubes or?? Of course, after applying the right load

[django49]

Okay, my disclaimer is that I am NOT a tech. However, this has worked for me. Check out this video. Seems counter-intuitive to me to turn ON an amp WITHOUT tubes in place, but I had success.

I am guessing the ohm mismatch probably did NOT cause a problem. At least unless you were pushing it hard. Very likely a defective tube.

It is a good idea to have extra fuses in hand, but this procedure should minimize the number of fuses you blow. Last TWO times I followed the procedure, the problem was a rectifier tube,so starting there is a fair idea. Having good replacement tubes in hand is assumed.

There is a fairly good possibility that you have not done serious damage.

https://youtu.be/wSl-l9aWDHws

[django49]

BTW, when I talked to Michael Swart re a problem with one of his amps, he suggested exactly the same thing.

Now and then I think solid state options, such as the new Quilter toys, make good sense. Painful as it is to admit it.

[fractal]

BTW, when I talked to Michael Swart re a problem with one of his amps, he suggested exactly the same thing.

Now and then I think solid state options, such as the new Quilter toys, make good sense. Painful as it is to admit it.

Quilter amps are not toys. They sound DAMN good. You should try one without any guilt.

[django49]

^^^

I was being facetious. I have tried a couple different ones and they are excellent!

The Aviator is a bit more straight forward (and works great with pedals). The MicroPro is a very versatile "Swiss Army Knife".

Lightweight but heavy duty.....Def NOT toys!

[Jakeboy]

Most techs will do what you want to do....replace the fuse and fire that bad boy up. Tubes, especially old USA and European tubes, can take a beating. It will either work as normal or have an issue which you will most likely notice immediately.

If the OT is destroyed, or is going out, you will hear greatly reduced volume and the tone will be greatly affected.

If a tube is going out, you can see or hear it.

If it were mine, I would simply replace the fuse and see what happens. If the tubes are worn or have been in the amp a long time, it might be time for a change anyway, though.

Was the 6l6 red plating? If so, look for it and if the plates start to glow red again shut down immediately and replace that tube.

Let us know what happens. Most Fender amps tolerate an ohms mismatch with no issues at all. Marshalls and other circuits not so much....with the exception being the Marshall Bluesbreaker (JTM45).

[veatch]

Take a look at your grid resisters on your power tubes and see if they are entact. Especially if they are carbon comp. I've seen a few overheat and crap out (crack).

If so, I would recommend checking voltages at the power tubes to see if things are in spec, and if so, replacing the grid resistors with wire wound flame proof at a higher wattage. The fuse should go before the resistor, not the other way around, but I've seen a few amps where the grid resistor goes first.

Note - I'm no expert, so take what I say with a grain of salt. Also note there are high voltages in an amp, even after powered of. If you are new to amps, consult a tech.

Hope that helps.

[crunchee]

Did the amp ACTUALLY smoke? I once fried a transformer on a small tube practice amp, I don't recall actually seeing smoke, but it smelled very much like a burnt tire when it quit working.

[Thundersteel]

An 8-ohm load on the 4-ohm tap should cause no worry, as the amp should have been only putting out half the rated power.

Now if it was a 4-ohm load on the 8-ohm tap, then that would be a cause for concern.

[sirDaniel]

okay, thought I would generate a consensus. My initial thought was bad toob, but I did notice the ohm mismatch. I really didn't think that caused it, but it was cranking stadium loud when she went.

[stobro]

An 8-ohm load on the 4-ohm tap should cause no worry, as the amp should have been only putting out half the rated power.

Now if it was a 4-ohm load on the 8-ohm tap, then that would be a cause for concern.

This is only true for amps that don't have output transformers, like solid state amps. Tube amps with output transformers react to impedance mismatch entirely differently.

[Thundersteel]

This is only true for amps that don't have output transformers, like solid state amps. Tube amps with output transformers react to impedance mismatch entirely differently.

Perhaps. Nevertheless, just as long as the output impedance is equal to or higher than the output tap, then you're good to go. Its when the output impedance is lower than the output tap is where problems start.

[Armitage]

An 8-ohm load on the 4-ohm tap should cause no worry, as the amp should have been only putting out half the rated power.

Now if it was a 4-ohm load on the 8-ohm tap, then that would be a cause for concern.

This is only true for amps that don't have output transformers, like solid state amps. Tube amps with output transformers react to impedance mismatch entirely differently.

Absolutely. The whole internet gets that one wrong. I think most people learned about impedance from wiring up car stereos...

[Armitage]

P.S. Don't smoke your amp, it causes cancer...

[stobro]

This is only true for amps that don't have output transformers, like solid state amps. Tube amps with output transformers react to impedance mismatch entirely differently.

Perhaps. Nevertheless, just as long as the output impedance is equal to or higher than the output tap, then you're good to go. Its when the output impedance is lower than the output tap is where problems start.

According to Kevin O'Connor from London Power:

A nominal 8-ohm load may reflect 4k to the plates of the output tubes with a given transformer. The amp might be designed to produce its maximum power into this load, with a designed frequency response. This is the "power bandwidth". If we change the load to 16-ohms, the reflected load doubles and the frequency response shifts upward. We lose bass but have a brighter sound, and also lose power. If we change to a 4-ohm load, the reflected impedance drops to 2k, into which the tubes produce less power, and the bandwidth is again narrowed.

The reason for the confusion, I believe, is that people think tubes will try to behave the same way transistors do. Into half the load impedance, a transistor will try to deliver twice as much current. The device may overheat and destroy itself in the process. Tubes, however, simply don't behave like transistors.

[sirDaniel]

thanks for the advice. I reloaded the fuse and put some new power tubes in and she works great. I think it was a 6L6 that gave up the ghost.

Now I can blow some shit up again. Loud amps moving gobs of air are what it's all about.

[Armitage]

This is only true for amps that don't have output transformers, like solid state amps. Tube amps with output transformers react to impedance mismatch entirely differently.

Perhaps. Nevertheless, just as long as the output impedance is equal to or higher than the output tap, then you're good to go. Its when the output impedance is lower than the output tap is where problems start.

Generally no, if the speakers output impedance is a touch higher, the output transformer gets hot, if it's a touch lower you don't have an issue. With transistor amps, it's the other way around for problems. That's why you cannot unplug the speakers on a tube amp, but you can with a transistor amp...

[Thundersteel]

Generally no, if the speakers output impedance is a touch higher, the output transformer gets hot, if it's a touch lower you don't have an issue.

Better tell that to Mesa-Boogie! This is from one of their amp manuals:

MESA/Boogie amplifiers can handle 4 and 8 ohms effectively. Never run below 4 ohms in a tube amplifier unless you are absolutely certain that the system can handle it properly; this can cause damage to the Output transformer. A few amplifiers can handle 2 ohms effectively without damaging them ( for example the MESA’s Bass 400+). You can always have a higher resistance (16 ohms, for example) without damaging results, but too low of a resistance will likely cause problems.

MIS-MATCHING: When running a higher resistance ( for example: 8 ohm output into 16 ohm cabinet ), a slightly different feel and response will be eminent. A slight mismatch can provide a darker smoother tone with a little less output and attack. This response is a result of the amplifier running a bit cooler. Sometimes when using more than one cabinet a mismatch will be the only option.

[cmatthes]

Crap.

My amp was smoking earlier too.

Something in the air?

[MOvalve]

thanks for the advice. I reloaded the fuse and put some new power tubes in and she works great. I think it was a 6L6 that gave up the ghost.

Now I can blow some shit up again. Loud amps moving gobs of air are what it's all about.

Happy ending! You're far more likely to smoke a tube and or socket in that kind of mismatch scenario. I've repaired many, many tube amps and have replaced all of 2 blown output transformers. Def best to match the load but I'm not quite sure how the internet made us guitarists have such a paranoia of blowing ot's. Glad your amp is a-okay.

[veatch]

^^^

I think for me, it's Murphy's law. As soon as something fails, i just know it will be the most expensive component to replace.

For example, as soon as i hear a funny noise from under the hood of my car, i immediately wonder if it is the supercharger...