[R-390] R390A audio amplifier

[Bob Camp]

Hi

The audio pot does not go to zero ….

Bob

On May 27, 2013, at 8:54 PM, Eric Gauja <ericgauja at optusnet.com.au> wrote:

> Hi Roger,
>                 Thanks for your reply, but I think you have misunderstood my question.  The break-in function on my R390A seems not to be at fault- the relay operates properly and in my case does completely silence the receiver. My question was really why turning the AF gain pot to its minimum position does not completely silence the receiver , because in the minimum position of the AF gain pot, the AF line is grounded, as is the case if the break-in function is activated.
> 
> Regards,
>                Eric.
> 
> From: Roger Ruszkowski 
> Sent: Tuesday, May 28, 2013 10:41 AM
> To: ericgauja at optusnet.com.au ; r-390 at mailman.qth.net 
> Subject: Re: [R-390] R390A audio amplifier
> 
> Eric,
> 
> The other thing that should happen when you go to break in is
> that the antenna relay should short the RF input to ground also.
> Thus you have no signal to bleed through to the audio and be
> noticed. 
> 
> Actually the AF shorting line on the cathode of V601B should pull
> the signal to ground. The break in relay does  in fact pull the cathode
> signal to ground. But you will get some audio bleed through.
> 
> Break in is to keep your ear drums in tack, not perform a full mute function.
> Looking at the circuit you would expect a very good mute operation.
> 
> The break in relay may not have had a lot of use lately and thus
> the contacts may not be a close to zero ohms as you would like them to be.
> They may read zero with a low current ohm meter, but offer a bit more
> resistance to an actual audio level signal. Using the break in will
> help clean the contacts with some regular operation.
> 
> Make sure the antenna relay part of the break in operation is working.
> It is common for the bridge rectifier to fail open and thus the antenna 
> relay is not operating. Also the little pins in the antenna relay will stick
> and not let the antenna contacts change state. You can clean the antenna relay 
> and restore its operation. A nice bridge rectifier can be installed if the
> original selenium stack has failed open.
> 
> There will be some audio bleed through in break in. The function
> is not a perfect mute.
> 
> Roger AI4NI
> 
> -----Original Message-----
> From: Eric Gauja <ericgauja at optusnet.com.au>
> To: r-390 <r-390 at mailman.qth.net>
> Sent: Sun, May 26, 2013 7:44 pm
> Subject: [R-390] R390A audio amplifier
> 
> 
> Dear Group Members,
>                                     I have a question about the R390A audio 
> stage.  The AF cathode follower V601B is connected to the grid of the local or 
> line AF amplifiers V602A  , V602B  through the volume control pots R105 and 
> R104.   The receiver can be muted by the break-in relay switch connecting the 
> cathode follower cathode resistor R627 to ground.  Complete silence.  Operation 
> of the break –in switch once more restores audio.  Good.   However, if the gain 
> volume control pot is turned to its minimum position, there is still audio 
> present at a low, but noticeable level.  Why does this happen? At the gain 
> control’s minimum position, is not the grid of the AF amp connected to ground 
> also?    
> 
> Best Wishes from Eric (Sydney, Australia)
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