Metropoulos Forum

Hey guys the amp was on and I was moving it not playing anything however but it was dimed and for some dumb reason I pulled the speaker cable thinking it was off and I realized one second later that it was on since I saw the tubes glow and quickly turned it off.

I was scared and mad. Anyway I turned her back on, no fuses were blown and it plays. But I am worried about the damage I might have done.

What should I look out for as in signs that my amp is damaged?

Well the only sign that you can do much about, is the power tube sockets. If there's any signs of arcing and carbon tracking on those, they'll need replacing. Tubes may be a little weaker, but at least they're still working. As for the OT, well it's pretty difficult to measure damage on any shortish coil without removing it and heat-soaking it to test the insulation (not recommended with this type of transformer) so you'll just have to take it as a lesson, and try not to worry.

Might be worth having a look at the screen resistors too.

What does carbon tracing and arching look like on the tube sockets?

Yeah I am going to check her out.

She also sounds a bit rougher, I think Im hearing a bit more noise and the notes are not as sweet sounding

Hopefully that's just the sound of toasted power tubes.

Carbon tracking looks like very fine black jagged lines in between the pins on the tube sockets. It's basically where voltages get really high and jump the easiest way that they can back to ground, and cause burning along the way. Unfortunately, these burn marks can be conductive, and even if removed properly (the only real way is by use of abrasives - not recommended), then they will still return quite easily. The integrity of the insulator has already been compromised by this point. Any other signs of burning by arcing is also not good, but carbon tracks are the real problem.

Thank you for replying and the information.

Is there a way to protect the circuit from such an incident, that if the speaker cable goes out the amp turns off or a different load is available.

However I did coat the tube pins with this

http://www.mgchemicals.com/products/4228.html" onclick="window.open(this.href);return false;

Would that help prevent the carbon tracks?

harkkam08 wrote:Thank you for replying and the information.

Is there a way to protect the circuit from such an incident, that if the speaker cable goes out the amp turns off or a different load is available.

However I did coat the tube pins with this

http://www.mgchemicals.com/products/4228.html" onclick="window.open(this.href);return false;

Would that help prevent the carbon tracks?

No, the carbon tracking and arcing will occur on the other side of the sockets where the tube plugs in, if at all.
Hang on, you coated the TUBE PINS with INSULATING VARNISH, or the solder connections???????

You could use a resistor on the switching side of one of the speaker jacks (a la fender) which would create a load when unplugged. Still not ideal, but better. The downside of this is you HAVE to plug your speaker cab into this jack when only using one cab. This would be the master socket. Personally, I don't like doing this.

I coated the solder connections, not the tube pins lol, sorry about the mix up.

harkkam08 wrote:I coated the solder connections, not the tube pins lol, sorry about the mix up.

I figured that's what you meant.
Phew, panic over.

Other day i plugged my speaker cable to the tremolo jack input :/
I get the amp on for a few minute, i tryed to play no sound, i kicked the fuzz in and still no sound(hate this one).
I close it, check behind and make the correct connection, no fuse blown and it still work flawlessly lol. it impressed me somehow(maby the shuguang kt-66 handle high current better or the ppimv saved it who know).
I guess the Power tube will have a shorter life now darnit(they where a few hours old only)

Ill learned the lesson me too :/
I will be checking the screen resistor just in case.

mathd wrote:I guess the Power tube will have a shorter life now darnit

Not to mention the output transformer.

demonufo wrote:

mathd wrote:I guess the Power tube will have a shorter life now darnit

Not to mention the output transformer.

Hopefully it make it sound more vintage/used up? joking .

I checked my screen resistor they are fine, but my bias and voltage drifted for some reason.( lost 7mA on tube and 3 volt on plate) That is probably because the tube has low hour count/breaking in.

If you only had it disconnected for a couple of seconds, and didnt have any signal coming in, you didnt hurt anything. it takes longer than people think to overheat the OT.

That being said, dont do it again.

[quote="hdahs"]If you only had it disconnected for a couple of seconds, and didnt have any signal coming in, you didnt hurt anything. it takes longer than people think to overheat the OT.

That being said, dont do it again. [/quote]

Agreed. If there was no signal going through the amp, everything is fine.

Exactly how bad is it for the amp to be on w/o connected to speaker? Is it a matter of seconds? What can be damaged? I've heard this is not a big problem with newer tube amps but more with older ones.. true?