Mark V weird problem Please help

[5tefania]

Hello this is my first post in the forum and unfortunately it's for a problem with my otherwise superb mark v head. I get this weird noise only when I use it on full power. Variac works ok. Even on full power I dont get it all the time but enough times that's it's becoming a nuissance. Most of the times it doesn't go though the speakers but the times it does it's really annoying and changes frequency. Any thoughts as to what this might be? I live in Greece (yes Greece) and I would have to pay an insane amount in shipping costs to send it back to Germany from where I got it. I have almost no experience in troubleshooting tube amps cause I really haven't had any problems in the past so if it's something basic please let me know. Here is a video of the noise so you get a good idea of what it is

http://www.youtube.com/watch?v=DyJfHAhsirw

Again any input will be greatly appreciated

 

[K-Roll]

have you tried a different power outlet? or try taking it to another place/rehearsal room etc. just to see whether it's a problem with your electrics or with the amp

 

[Adambomb]

Have you checked the fan?? Sounds like it may be scraping against something, I dont know. Or it could be one of your four power tubes.

 

[search4tone]

I'm going to throw out a wild guess; try replacing the rectifier tube. A wild guess because watching the video it sounded more pronounced when you were close to the rectifier tube. I think that the tube doesn't have to work so hard in the Variac setting. Does it make a difference if you have all the channels switched to SS rectifier?

 

[thalweg]

Its a pain in the nut sack...but swapping tubes is your first move after of course, checking cables and making sure this happens in all channels and or power settings 10w to 90w

Also, what is the electric system in Greece 220v-240v? if so, did you buy a factory conversion or was it converted after the fact for this?