Mark III Simul Redplating on two adjacent power tubes sockets (6L6 and EL34)

Mark I's, II's, III's and the almight IV

Moderators: Guitarzan, Grandor, ned, Platypus

Post Reply
Red3
Bottle Rocket
Posts: 4
Joined: Thu May 16, 2019 4:37 am

Mark III Simul Redplating on two adjacent power tubes sockets (6L6 and EL34)

Post by Red3 » Sat Nov 09, 2019 6:42 am

Mark III Red Stripe, Simulclass is redplating on two adjacent power tube sockets (6L6 and EL34). I've tried swopping out tubes same result. The plate current on these tubes runs very high (80ma). The other side (6L6, EL34) the bias is steady and in spec. Any thoughts would be great, thanks.

JD
Donating Member
Posts: 180
Joined: Sat Jun 16, 2007 3:27 pm
Location: Australia

Re: Mark III Simul Redplating on two adjacent power tubes sockets (6L6 and EL34)

Post by JD » Tue Nov 12, 2019 5:38 am

Check to see if C511 or C512 are not shorted
Mesa Boogie Mark 3++ RGX 60W
Axe fx 2
Mesa Boogie Quad Preamp with C+ Mod Ch1 C++ Ch2
Mesa boogie Studio pre with C++ Mod by Mike B
Mesa Boogie Studio pre with C++ Mod

woodbutcher65
Mark III
Posts: 211
Joined: Fri May 04, 2018 10:36 pm

Re: Mark III Simul Redplating on two adjacent power tubes sockets (6L6 and EL34)

Post by woodbutcher65 » Fri Nov 29, 2019 12:20 am

JD probably hit it in one. If a coupling cap shorts (it'll be a .1 uF 600 volt orange drop) then the tubes on that side of the OT will lose bias and will red plate. It's recommend to replace both coupling caps as as pair.

Been there, done that.

Post Reply