[R-390] R-390A -relay problems.

[Tim Shoppa]

Bob writes:
> Recently on start up from off to standby I get a loud buzzing noise for a 
> few seconds then a click and the power goes on which sounds like a bad 
> relay, when I click it to AGC from standby I get another click which sounds 
> like another relay and this one (?) works fine, are there two relays in 
> 390A's? I always assumed there was only the antenna relay. If there are two, 
> which one would close from off to standby as it is going to go kaput very 
> soon. Once the radio has been on for a while it will shut off and on fine 
> from off to standby, it is only from a cold start that i have a problem, 
> thanks,

The antenna relay is run by 25VAC that has been rectified to 120Hz approx
20V average pulsating DC by the selenium rectifier CR102.

If half of the selenium bridge has failed, you get 60Hz approx 10V average
pulsating DC to run the antenna relay coil, and you (no surprise) end up with
a buzzing relay.

The breakin relay is run by 6.3VAC.

But... have you possibly (either internally or externally) installed a
inrush current limiter? This will cause the buzzing on cold startup
symptom you're reporting too, and is perfectly normal with an inrush
limiter.

Tim.