JCM 900 2100 SLX Bias Problem

[hadley101]

Just picked up JCM 900 2100 SLX with 5881,
unfortunately it came with Tung Sol 5881 and
they couldn't cope with plate voltage.

TS 5881 rated for 400V and one tube went poof
within a day.

Got a set of TAD 6L6GC's and installed them and thus
my problem, no matter where the tubes are swapped
around V5/V7 come in @ 40 ma and V6/V8 @ 60 ma.

I'm getting 470v plate voltage and -90
grid voltage off pin 5 on all 4 tubes.

Checked all screen resistors 470ohm and they
are fine, nothing really scorched on the board.

Getting 490v on screen pin 4

I'm at a loss, looking for some help and
guidance as where to troubleshoot next.

Appreciate any help anyone can give
me


Thanks


http://www.drtube.com/schematics/mar...slxa-61-02.gif

http://www.drtube.com/schematics/mar...2100-60-02.gif

http://www.drtube.com/schematics/mar...2100-60-58.gif