QST, Jan 1958, p. 127.
QST, Jun 1963, p. 161. (NOS?)
The 19-tube 51J-4 was the final receiver in Collins' 51J series. It was similar to the 51J-3 but used the company's mechanical filters in its 500kHz IF.
References
Modifying for SSB reception. Ham Radio, Feb 1978, p. 66.
