[R-390] Lost local audio - please help

[Larry H]

Hi Chris,  There's a good chance it's V603, the local output tube, a 6ak6.  There's a slim chance it's V602, it's driver.  The audio is pretty solid except for a couple caps in the common section.  Try swapping V603 and V604.  I hope that's it as your next step would be to measure the resistance of the output transformer - it's easy to start with pin 6 on tb 102 to gnd.
Good luck.  Regards, Larry

      From: Chris Kepus <ckepus at comcast.net>
 To: R-390 at mailman.qth.net 
 Sent: Wednesday, February 24, 2016 10:40 PM
 Subject: [R-390] Lost local audio - please help
   
Three nights ago, I was enjoying my Collins R-390A while tuning around on
20M and 40M listening to sideband and CW stations. Last night, however, I
turned on the set (same control settings as the night before) and waited for
it to warm up....and waited.... but no noise came from the speaker and there
was no change by increasing the local audio control.  It was late and I was
tired so I turned it off. 

Today, I pulled the block diagram (the set has worked perfectly for many
years so I've never had the pleasure of opening it up for troubleshooting)
and noted that the local audio amp and line audio amp are basically in
parallel. Turned on the set.. waited, but the result was the same as the
night before.  Then turned up the line audio....and there is audio that
sounds "good" and all other functions are working normally.  

The problem is located in the Local Audio amp circuitry and / or one of the
tubes in this section gave it up and failed suddenly. 

Are there any components in this area that have a high failure rate?  All
comments and suggestions welcomed.  It will be awhile before I get some help
to pull it out of the rack (need assistance with the weight) so I can get
into it.  

Thanks,
Chris
W7JPG

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