Mystery Of Red Plating


My tube amp (ARC VT130) was blowing up her screening resistor on the left channel. The two Sovtek 6550 tubes would glow red- pulsating with red heat. If it weren’t so disastrously bad for them it would be fun to watch. I assumed it was a bias problem. I also

replaced resistors - more than necessary but as the story will tell not the right one. As it turns out it was bias- and a lot more! I had a resistor with a pin hole in it that was arcing to a trace on the printed circuit board which was pushing 100volts into a triode tube ( a 12BH7A) which is a voltage controller for the 6550s.

https://imgur.com/gallery/f9E1Yqd

 

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I had to wait 8 months to get in line at ARC. I think the repair cost with shipping was $3,000. The Audiogon Blue Book says my VT130 is only worth $3000.  Gee thanks! 

The ARC guy told me since the spamdemic "everybody" was taking their old gear out of mothball and sending it in for refurb- hence the wait. ARC must be making a killing on restoring old gear.

A musician buddy of mine told me to call the music store in at the local mall. They would know of local technicians that worked on tube amps (Fender mostly). 

Lo and behold they were right!  A dude named Matt Garcia had a store front repair shop called Garcia Amplification in old Myrtle Beach SC. He fixed the unit for $300 all in!  What a deal!  Moral of the story: Support your local electronics man.

2 Sylvania NOS 12BH7As $60

2 5K ceramic resistors       $5

Materials and Supplies     $25

Diagnose, test all 14 tubes, replace 3 resistors, 3 tubes, bias L&R, $210

Total cash out the door $300.  It took him a week.  

I had an amp red plate and it’s scary.   That’s why you should never leave a tube amp on if you’re not close by.   

Awesome ending.   There are still some good local techs , it’s finding them that’s a challenge 

In the Boston area D&S Tube Audio does repairs and mods on HiFi  and guitar amps.   He’s in North Attleboro MA