Collins 75A-4 Initial Sensitivity Check (pre alignment checks)

This Collins 75A-4 has been recapped and has had four out of tolerance resistors replaced. This short video shows an initial sensitivity check at 14.5MHz using my recently refurbished HP8640B signal generator, which has a calibrated output level adjustable down to -145dBm (approx. 0.02uV). The 75A-4 could detect CW signal down to around -140dBm (0.0224uV) with the 500Hz IF bandwidth filter in circuit, and AM signals down to around -130dBm (0.071uV) with the 3.1KHz IF filter in circuit. The spec. for the receiver is 1.0uV for 6dB signal-to-noise ratio with 3KHz IF bandwidth (it does not specify on CW or AM). So, not a bad result considering the alignment has not been checked/adjusted if needed!

[@zdzisiek1979]

Bardzo mi się to radio podoba ... cudo dawnej epoki. Pozdrawiam

[@RadioRestoration]

Yes, its a beauty! - almost the same age as me, though I think it has been better looked-after...(!)

[@joelima201]

That's a Collins performance !

[@RadioRestoration]

It certainly is Joe! - this is a lovely radio...