[R-390] R390-A problem

[Shoppa, Tim]

Sounds like cathode to filament short (hum is the smoking gun but the gain shift is telltale too). These are often intermittent. Switching to or through standby interrupts B+.

Most likely it's any of the 5814A's and I'm guessing somewhere after the detector.

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Robert Young
Sent: Monday, January 31, 2011 12:21 PM
To: r-390
Subject: [R-390] R390-A problem


Hello all,

The radio works normally then after about a ten minute warm up the volume jumps up maybe double (normal listing level with local gain on 0) and 120 cycle hum is audible. If I click it from AGC to standby or AGC to calibrate and back it drops down to normal volume again for a few seconds then goes back up, it's almost like something is not conducting and needs a little voltage spurt to get going again. This was intermittent when it first started a few years ago but is now predictable although it was sometimes go back to normal by itself. Everything else is the same either way, just the volume jumps up (I have to turn down the RF control to get it silenced) AGC seems to be working normally. This radio was restored by Chuck Ripple about 5 years ago and i have changed some tubes since then but have pretty much left it alone besides tubes, it works great except for this little annoyance. The power supply was solid stated by him. I'm wondering if a cap in the audio chain is on it's
  way out. I have another audio module but it's inaccessible right now. I suspect something in the audio section, anyone have any ideas? 

Bob Young
KB1OKL
 		 	   		  
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