R-390A Local Gain

[W7SOE]

Hello All,

   My R-390A local gain does not go low enough.  If I turn the RF gain up all the way and the local gain all the way down, the volume is too loud.  I ohm’d out the LG pot to 2.3K, seems ok.  Oddly enough, when I grounded the wiper of the pot (with it turned all the way down soas to not smoke it), I still had audio output……..

 

Perhaps this audio “offset” is normal. I hope not.

 

 

Thanks

 

Rich

[W2XR]

In my R-390A ('67 EAC), there is some low-level audio output with the Local Gain control at full counter-clockwise rotation. I believe this to be a normal condition for this receiver.

But in my case, the volume with the Local Gain control in the minimum gain position is far from loud. I take the audio from terminals 7 and 8 of TB-102, with terminal 8 being the hot-side of the unbalanced 600 ohm output, and terminal 7 being the shield/ground return.

I am driving a triode-connected EL-34 (Altec-Lansing 1568A) power amplifier from the Local Output of my R-390A, and the drive level from the receiver is a very good match to the gain of this amplifier. Plus I am using a very efficient loudspeaker (102 dB SPL/one watt/one meter) with this combination.

Perhaps you are using an amplifier with too much gain. You should probably be using an amplifier with sufficient gain so that the approximately 1 volt of audio from the R-390A will drive it to essentially full output. The Local Output fulfills this output level requirement, and this is the input level nearly all consumer/professional audio power amplifiers (or integrated amplifiers using any of the auxilliary inputs, such as CD, Tuner, Tape Out, etc.) require for rated output power.

73,

Bruce

[W7SOE]

I am not using an external audio amp, I am using a Hallicrafters R-42 reproducer (600 ohms) connected directly to the local audio output.

I am still mystified when I get (albeit muffled) audio output when I ground the grid input to the first audio stage.  Will have to re-examine.......

Rich

[Ed/KB1HYS]

My R-390A is the same way, I never use the Audio gain control. It's always at or near min. I use a small xformer to impedance match the 8 ohm speaker to the 600ohm output. I never thought much about it.  I compensate by using the RF gain to reduce the output, and "fine tune" with the audio gain, if necessary.    Adding a pot in the line to the speaker would probably an easy fix...

[W7SOE]

My R-390A is the same way, I never use the Audio gain control. It's always at or near min. I use a small xformer to impedance match the 8 ohm speaker to the 600ohm output. I never thought much about it.  I compensate by using the RF gain to reduce the output, and "fine tune" with the audio gain, if necessary.    Adding a pot in the line to the speaker would probably an easy fix...

Hmm, perhaps I should stop try to fix it.....