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 Post subject: Drake R4A- rf gain control issue
PostPosted: Feb Thu 08, 2018 12:58 pm 
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Joined: Aug Fri 08, 2008 3:21 am
Posts: 47
Location: dexter mi.
Newly acquired R4A with a strange (to me) issue.With the rf gain control set to max,the receiver sensitivity seems good.However when
turning the control back down, reception only reduces a slight amount- even with the control at the "off" position.Also the S meter reading
only changes a small amount from min to max of the rf gain. Any suggestions as to what is going on in the circuit ? TIA Jeff


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 Post subject: Re: Drake R4A- rf gain control issue
PostPosted: Feb Thu 08, 2018 1:33 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5625
The RF gain control in the R-4A changes the bias on the AGC line so it works as part of the AGC system. Does the receiver go into standby properly when put in standby position (S meter should go to full scale and the audio should mute?

The adjustment of the 1K gain pot (set during alignment) will have an effect upon RF gain control operation but I would expect even with this control set incorrectly you would have more impact from changing the RF gain setting.

Does the problem remain the same in both the fast and slow AVC positions? Leakage in C108 (both positions) or C109(only used in slow AGC position) will pull down the AGC bus and result in full gain.

Rodger WQ9E


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 Post subject: Re: Drake R4A- rf gain control issue
PostPosted: Feb Thu 08, 2018 4:39 pm 
Member

Joined: Aug Fri 08, 2008 3:21 am
Posts: 47
Location: dexter mi.
Switch in standby position-S meter goes full scale both fast and slow AVC. With a S-9 signal- switching to standby with RF gain set to "0",
Volume at 3/4 on- audio is clearly heard. Sounding like a leaky cap in the AVC circuit ? Thanks for the input.


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