2N5457 Preamp Circuit

A simple JFET preamp circuit that I integrated into the Simplex PB receiver to improve the RF sensitivity. Again, the amplifier increases the entire noise floor, so noise in noise out.
The playlist for the Simplex Model PB restoration:
• Simplex Model PB | Res...
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[@W1RMD]

Thanks Don. Take care.

[@RestoreOldRadios]

Thanks for watching Ryan. Best, Don

[@DERB_Seymour_Indiana]

Nice little circuit Don, thanks for sharing. :)

[@RestoreOldRadios]

Thank you Doug. Best, Don

[@ordinaryaverageguy76]

In addition to increasing the noise floor, as noted, an untuned input can be susceptible to unwanted mixing of strong, off-frequency or even out of band signals, creating strange problems with distortion. Just something to beware of. I had a receiver with a similar untuned preamp & the neighborhood CB operator randomly appeared on all bands.

[@RestoreOldRadios]

Great points! Sorry for my belated response, I got focused on the Grunow and forgot to reply back. Thanks for your feedback and all the best to you. Don

[@ScottGrammer]

Would adding a choke in parallel with the 100K input resistor improve matters by preventing the FET from amplifying low frequency noise, like 60Hz hum fields? Say, a few hundred microhenries?

[@RestoreOldRadios]

I’m sure a high pass filter on the front-end would help mitigate such… one modification to try for sure. Thanks for reaching out and watching. Best, Don