Vintage Hallicrafters Shortwave Receiver SX-99 Digital Frequency Display Install

In this episode I discover that the add on of a digital Frequency Display is simpler than anticipated.

[@DonnyHooterHoot]

I connected mine to a 7 tube AM radio. I went through a 103 cap and a 4.7M ohm resistor to pin 5 on a tube. Works like a charm.

[@radioman140]

nice job and thanks for the upload. A nice improvement for getting frequency accuracy outside the amateur bands.

[@mattw7734]

Very nice! I want to do the same thing to an s40b. What tube do you tap into for the frequency signal?

[@i82996]

The SX-99 has a 6SA7 mixer tube that combines oscillator with mixing the incoming signal with the IF frequency available through the IF transformer on the plate. The best tap point on the mixer tube is the cathode so the tap does not drag the oscillator. It is important to install a buffer circuit, which is a custom PC board along the lines of the buffer circuit that Mr. Carlson's lab used on a Hammerlund install some years back. The video is still there on his channel.

[@gixerags750]

Hi , those 2 Tronson attenuators , have you modified them or do they work as is ? Cheers

[@i82996]

@@gixerags750 they work as is

[@gixerags750]

@@i82996 no worries , I have one but I saw some dodgy reviews. ✌️

[@jameshall5835]

It looks like a Molex connector on the back panel that you are using to connect the counter to the radio - could you state which one please ? Also you stated that you are using 7VDC to power the counter - how are you arranging this ? I’ve ordered parts to do exactly this with my SX-99. 73, Jamie WB4YDL

[@i82996]

Hey James I am at my Dad’s but I think I used Mouser 538-76650-065 four pin connector but any four or three pin will do. One pin is power, one pin ground and one signal from the cathode (shielded at the connector side). The 7 vdc (unloaded) is fed from the 6.3 vac filament lead to a 2w 22ohm resistor to a shotkey diode parallel, i think, with a .1 mfd cap to a 2200 mfd 50 vdc electrolytic filter cap, which provides a nice dc voltage for solid state things. I mounted this on an ordinary terminal strip near the radio power supply area and used a simple multistranded insulated wire to the connector. The simple rectified power supply is drawn on one of Mr Carlsons Lab youtube videos 2 or 3 yrs back, as an add on for a Hammerlund restoration, I think.