[Orpheus]

hi.... well, I have a MG Head, and i heard it doesn't work well with low-impedance headphones. i usually use it with a hd600 (300 ohms,) but i just received a hd280 pro, which is 64ohms, so i tried it in the mg head....

i played around with it a bit... turning the amp off and on a couple times to try various things.... but then all of a sudden i heard a loud hum in one channel. well, i thought my mg head was acting up again (i've had 2 previous mg heads with bad hum).... so i decided to let it cool down then turn it on again. same thing. then i tried it with the hd600, same hum.

so, then i switched the el84 tubes out to new ones i had lying around and the hum was gone! so then i switched back to the original tubes and the hum was back. switching left for right, caused the hum to also switch stereo sides. so i guess it's just one tube broken.

but anyway... this is strange to me, cause i might have used this amp at most 20-30 hours. maybe turned it on 30 times. not much use. so i thought the tube would have much more life left (Ei Elite Gold el84's).

what do you think?--just coincidence that the tube broke? or is possible using lower impedance headphones could cause tube damage?

orpheus

 

[bootman]

Quote:

Originally posted by Orpheus hi.... well, I have a MG Head, and i heard it doesn't work well with low-impedance headphones. i usually use it with a hd600 (300 ohms,) but i just received a hd280 pro, which is 64ohms, so i tried it in the mg head.... i played around with it a bit... turning the amp off and on a couple times to try various things.... but then all of a sudden i heard a loud hum in one channel. well, i thought my mg head was acting up again (i've had 2 previous mg heads with bad hum).... so i decided to let it cool down then turn it on again. same thing. then i tried it with the hd600, same hum. so, then i switched the el84 tubes out to new ones i had lying around and the hum was gone! so then i switched back to the original tubes and the hum was back. switching left for right, caused the hum to also switch stereo sides. so i guess it's just one tube broken. but anyway... this is strange to me, cause i might have used this amp at most 20-30 hours. maybe turned it on 30 times. not much use. so i thought the tube would have much more life left (Ei Elite Gold el84's). what do you think?--just coincidence that the tube broke? or is possible using lower impedance headphones could cause tube damage? orpheus

Well, if the tube was due to break then the extra current draw due to the lower impedance might have done it in.

 

[Hirsch]

Quote:

Originally posted by Orpheus but anyway... this is strange to me, cause i might have used this amp at most 20-30 hours. maybe turned it on 30 times. not much use. so i thought the tube would have much more life left (Ei Elite Gold el84's).

Some tubes just go noisy. There is no real pattern to it, except that if they do so, it's likeliest in the first month of use. If they get past that point, the risk goes way down, and the tube is likelier to sound good until it wears out. It can happen no matter how throroughly the tube is tested (I've had it happen to a tube I got from Upscale Audio, which does the most thorough testing I can imagine from a tube dealer. They replaced the tube with no hassle). Sometimes, it just happens.

 

[kwkarth]

What you've experienced is probably a short between the heater filament and cathode emitter of the tube. Definately a bad tube, and probably not the result of any overloading on your part. See if you can get it replaced under warranty.