[R-390] Line audio output problem and 6C4 RF tubes

[John Flood]

Greetings all!

Working on another R390A.  This one a "67 EAC" Dawg, all EAC modules but non matching serial numbers.  Local audio is fine but line output has a problem.  No audio across the output.  However one side of the line to the center-tap has audio but the other side to center-tap has no audio and the VU meter is bouncing away(yes the jumper is in place).  I haven't had a chance to dig into this yet but was wondering if anyone has seen this as well to possibly save me some time.

Also when powered up, this one,on local audio, it made noise but was deaf.  Looking into the RF deck first I found all three of the 6C4's bad( only slight deflection on the TV7.  This worried me a bit so then each tube was removed and tested.  A couple of hours later(that is the time you wish that heaters warmed up quicker!) all other tubes tested strong and with new 6C4's in place it was working.  I jokingly asked if it had taken a lightning hit!  All of the 6C4's looked to be of the same lot number and one could guess that  lot had quality problems  but I still thought it strange.  Any thoughts on this or is it one of those unsolved mysteries that I should forget about now that it is working?

John Flood KB1FQG
978-979-2807