I was warming up my Ming Da MC88-C the other night when I smelled something nasty burning. I looked over and all the lights were out on the amp. The fuse was blown, and when I opened the amp up there was a fried resistor under one of the power tube sockets. I got brave tonight and replaced the fuse and put all the tubes back in except the one, and everything fired up OK. All the power tube sockets have that same value resistor, I think it's a 10K ohm (brown, black, red, gold). I'm wondering what the chances are of that being the only problem, and what could have fried it. I did hear a slight hum coming from that channel a few days earlier. Any thoughts?

Is it under some kind of warranty? Send it back!

If you have a multi-meter, replace the resistor and take readings of the same resistors on the other power tube sockets without the tubes. If you get identical readings to the other three, then the output tube went belly up!

If you don't get the same readings as the other three without the tubes, you have a short somewhere else that caused that resistor to burn up!

You need to somehow test those output tubes before you power that unit up again.

Ummmm......lemme see, nope, no warranty. :no:

So, you're saying replace the resistor, power up with no tubes, and if the reading across that resistor is the same I'm good to go and it was just a tube that took a dump? That almost sounds too easy. Come to think of it, the last tube in that socket took a dump after around the same number of hours (500-700 give or take a few?):para:
Thanks for the advice, I appreciate it ;)

Actually brown-black-red is 1K ohm. Red is 2... that means multiply by 10 to the second power, or 100 times 10 (brown black).

I'm guessing, and this is only a guess, without a schematic, that a 1K resistor is either an input resistor or a screen grid resistor. It is possible for a tube to short, and cause this problem with either one.

And, as burned as that resistor is, there's no real way that it's going to read within spec. So, until that resistor is replaced, you can't really tell if the readings there are the same as the corresponding resistor positions on the other tube sockets.

Regards,
Gordon.

I agree with Gordon, that resistor looks like an input resistor. 1KΩ was often used. Do you have a way to test the tubes?

You guys are correct. It's a 1K ohm resistor. I was using a chart and reading it for a metal film vs a carbon film and it gave me 10K. I've been talking to a tech and it is, indeed a screen resistor. How the heck do I know the watt rating? I measured across the others and it's like 493V on one side and 488 on the other. The fried one was 493V on both sides, of course.

You guys are correct. It's a 1K ohm resistor. I was using a chart and reading it for a metal film vs a carbon film and it gave me 10K. I've been talking to a tech and it is, indeed a screen resistor. How the heck do I know the watt rating? I measured across the others and it's like 493V on one side and 488 on the other. The fried one was 493V on both sides, of course.

Watt rating is generally seen in the size of the resistor - the bigger the resistor the higher the wattage. I believe resistors come in standard 1/4,1/2,1,and 2 watts and then you start getting into power resistors. I believe that is a 1/2 watt resistor. Wait for someone else to chime in and confirm. I am still pretty new to this and could be wrong.

Mark

Hey Rob, I meant for you to replace to the resistor and take ohm readings with the new one, and the other three without the output tubes, before you even plug it in and power it up.

If they all four look the same or identical in readings, then you most likely had the one output tube develope a short.

Then plug it in and turn it on without the output tubes, and take a voltage measurement. If all four look ok, it was probably just that one output tube that went t**s up!