Dual rec. - Lightning show - blown rectifier tubes...HELP!

[chrisefekt]

Hello All,

Happy to have found the Boogie Board. Need some help from you guys. I bought a 2-channel dual rec. obviously used. At rehearsal I was greeted with a lightning show. I shut the amp down, and found out both rectifier tubes were blown, and there was a scorch mark on one of the power tube sockets. Called euro-tubes and ordered JJ GZ34 rec. tubes. EL34L power tubes and balanced pre-amp tubes. Decided to open up the amp before switching everything over, and noticed a burnt resistor on the circuit board between r-501. What is this for...protection? What do I need to replace it. Have to get it fixed right away, think I can do it myself? How should I dis-charge this amp? Any help or suggestions would be awesome. Thanks!

Chris

 

[Boogiebabies]

I wanted to avoid this one, but it looks like your in a jam.

Current Mesa schematics do not detail the board position of the caps and resistors, so we do not know what R501 is or what it does. Also, we don know what circuit board revision your DR is as they have tweaked them over the years. I understand that you want to fix this yourself, but it could be dangerous and costly. You should drain the caps to ground with a device that uses a resistor and two alligator clips to ground, but this is still dangerous if you goof. Secondly, why did R501 etc. go down. You can change the resistor and if you are not very careful you can lift the circuit pads from the board and your screwed. The heat from a soldering iron is not very nice to these boards. In general with Mesa's, blown resistors are either for the screen grids or bias supply. If you post a good clean shot of the circuit board, we can probably help you figure it out. It would be good to know if it's totally dead or the rsistance has dropped. Also, the carbon on the sockets is very bad. Most techs would replace the sockets because they know carbon does not conduct electricity and it a pain to remove. If you dont get it all, you can have noise, pops and it may prevent the tube rectifier circuit to not work. Your sockets are ceramic so there is a good chance you can clean the tube pins with contact cleaner and a dental pick. The older phenolic sockets used to be useless and not only the pins, but the housings would carbonize as well.

Good Luck.

 

[chrisefekt]

Thanks for the reply. Wanted to let you know that this amp is back to life! May sound like a stupid idea, but I went ahead and changed the tubes out, cleaned the sockets and fired it up (the band mates were hacking on me to get back to rehearsal). Works fine...nothing abnormal at all. I must say the EL34L JJ's sound awesome!!! That's the sound I was looking for. Clean is...well cleaner than I thought, but breaks up nice when I crank the gain dial. Alla Brit style, but that's what I wanted. And the distortion side sounds sweet, still has a bottom end to it like a 6L6 but with that EL34 character and plenty of gain. I Love these tubes. The GZ34's are more focused as well. Lost the flub. Very happy with this amp now. Rec owners do yourself a favor and try these tubes out! I play all styles of music. Want to order 2 KT88's and try to run them integrated with the 34L's. I'll let you know.

 

[Storm]

So the amp runs fine without replacing the blown R501 resistor?

Ciao ...

 

[chrisefekt]

Yes...seems to be fine!