# Frequency Display for Old Tube Radio

I have a Hallicrafters S-120 1960s vintage vacuum tube receiver (an "All American Five" superhet with solid state rectifier replacing one of the "five" tubes). It works well, doesn't have excessive internal noise, and seems very sensitive (with the regenerating IF used for "exalted carrier" on AM, and as a BFO for CW and SSB).

I've considered using this as a secondary receiver, for some version of "split" operation.

The problem with that is that, while the tuning is plenty precise (with the Bandspread control allowing several turns of a secondary tuning knob to cover a few hundred kilohertz), the tuning indicator needle is significantly off the actual tuned frequency (correctable) and doesn't move at all when using the Bandspread. I had the idea to connect a digital frequency display, which would allow me to see exactly where I'm tuned. I have such a display on hand, built from a kit.

The only place I see to get current tuned frequency from a superhet receiver is to tap into the local oscillator. Am I correct in thinking this will give a frequency 455 KHz below the actual tuned frequency?

• More likely that the LO is 455 kHz above the tuned frequency. – WA9ZZZ Apr 17 at 2:13

• Thanks. The one I have is the cheap 4 1/2 or 5 digit one, $15 for kit on eBay. Pretty sure it's microcontroller, but also near certain that programming isn't accessible. Might be worth getting an Arduino and doing some experimenting. – Zeiss Ikon Jul 17 '19 at 19:01 • @ZeissIkon I'm surprised that you can't find one that will work with your radio. The listing doesn't necessarily have to include Hallicrafters, as long as it is for a radio with a similar circuit. Besides eBay, I suggest you check on the qth.com etc. for sale listings. – Mike Waters Jul 17 '19 at 20:27 • eBay has many$10 8-digit counters (search for "Cymometer") that include an LO offset feature, reached through an obscure menu. They're totally unshielded and may interfere with your receiver – tomnexus Jul 17 '19 at 21:18