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i have a DR105 that blew the 3A HT fuse. it sounded great before the fuse blew. i replaced the fuse, fired it up and then it started crackling and buzzing really bad. i noticed a smell and shut it off. one of my power tube sockets had a burnt spot on top that also burned the bottom of the tube. i opened it up and everything else looks fine. i measured the resistors on that socket and they were correct. the tubes are pretty new so does this sound like a shorted tube? i also noticed the new HT fuse didnt look blown but it had a faint black ring around the center of it. any ideas on this?

Something made the tube arc, and once the carbon is there, it'll just keep arcing. The carbon is like a freeway for electricity.

You can try very carefully cleaning the socket (I would also use a different tube) and see how it goes.

When a severe fault occurs -- such as a shorted tube -- the HT fuse will flash and the whole glass will look silvery or blackened. When it just barely blows (as it often will when arcing starts), it will be hard to tell it is open by visual examination.

--mark

Buzzardstein76 wrote:it sounded great before the fuse blew

Isn't that always the way it goes?

I had something similar situation with my 105 a few weeks back. I retensioned the sockets very tight used contact cleaner cleaned the pins on the tubes and there hasnt been a problem since.

In 1974 I bought (for $700 ) an "English Mars Hall" Super Lead 100 (purchased by a wealthy friend in Canada in 1972).... MAN...That Thing ROCKED !!! (it's also how I earned my AKA: "Count Decibel") Anywhew...during one rehearsal...all was well...then FRITZ !!! An octal had arced between pins (I forget) and it FRIED the Output Transformer. Now, this being Miami...and 1974...forget replacing w/a Drake...the "Repairman" I took it to replaced it with "an American Equivalent"...and he also showed me the "Carbon Trail" (arc), that he then scraped clean and coated with "Rid-Arc". He gave me the bottle and said: "Take it home and coat ALL the octals between those 2 pins with same. I did. NEVER AGAIN...did it arc..... Now...it also NEVER SOUNDED THE SAME w/that Output tranny.... Oh, well....