carvin XV-112E problems

[chris025]

this amp was passed down to me from my father and now its really sounding like it needs help. When i pull the overdrive knob i get good overdrive for about a minute then it starts to crackle and fade out to nothing and also when i turn my reverb knob all i get is a loud buzzing sound. I would really appreciate the help

Thank you

[Gtr_tech]

Sounds like either a failing switching Jfet, or a leaky coupling cap driving a stage into cutoff. Look for DC on the first 2 preamp tube grids. If you don't find any DC there then I'd look to those J175 switches.

[BackwardsBoB]

Galvanic corrosion at reverb?

I've found that the old Carvins frequently lose the connections to the reverb tank, usually at the tank. I think it may be Galvanic corrosion. Clean up the connectors on the ends of the reverb and the mating connectors, and maybe give the ends on the cables a little squeeze. Then twist them around a bit when you re-install them. You can do it without pulling the chassis. Check the levels on that pack of inverters that do most of the drive for the channel switching too, and if you get a chance, change the screen resistors to 1K 5W, especially if you've got one of the older 6L6 models.

Super great amp once you get it cleaned up. You can find schematics at Carvinmuseum.com in the tech info section.

[Gtr_tech]

I've found that the old Carvins frequently lose the connections to the reverb tank, usually at the tank. I think it may be Galvanic corrosion. Clean up the connectors on the ends of the reverb and the mating connectors, and maybe give the ends on the cables a little squeeze. Then twist them around a bit when you re-install them. You can do it without pulling the chassis. Check the levels on that pack of inverters that do most of the drive for the channel switching too, and if you get a chance, change the screen resistors to 1K 5W, especially if you've got one of the older 6L6 models.

Super great amp once you get it cleaned up. You can find schematics at Carvinmuseum.com in the tech info section.

A 6L6 output section won't need 1k 5w screen resistors, that only applies to EL34s or other straight pentodes to limit screen current a little more.

The reverb is op amp driven, so I wouldn't rule out a bad drive/recovery op amp.

[BackwardsBoB]

If a screen circuit's bad enough, even a 6L6 can blow it...

Gtr_tech wrote:

A 6L6 output section won't need 1k 5w screen resistors, that only applies to EL34s or other straight pentodes to limit screen current a little more.

The 6L6 screen resistors are as low as 22 Ohms before replacement. Tube shorts cause quite a bit of damage, cooking the 22 Ohm resistor and blowing open R121 with lots of pyrotechnics. Rev. K had 470 Ohm 1W. Later 6L6s used 220 Ohms 2W. It took them a while to settle on 350 Ohms 5W at all locations with EL34s. I have several 6L6 based X-series chassis that have been damaged by screen current overload.

Later 6L6 X-series and all the EL34s don't have a bias pot, and we don't know what somebody's going to stick in there, or if their speaker has an open circuit.

I recommend a screen resistor beef-up on all models. Adds a hair of compression too.

The EQ assign switch can get dirty and go open too. If you toggle it 20 times with the power off, and the problem gets better or worse, the switch needs cleaning or replacement. I've heard you can take apart some of the switches.