So, why would you need an 8-digit counter display on a President Madison CB base?
Simple answer is you don't. 6 digits are plenty. But this customer wanted it, so here's what we found getting it installed.
There are a few differences between this one, the SanJian PLJ8-LED display and the 6-digit PLJ6-LED we normally use. Biggest difference besides the extra two digits is the voltage regulator. The 6-digit version has an analog regulator. This one uses a switchmode-type.
This increases the digital noise this thing generates, and we had some issues with "zing" noises in the receiver audio.
We mounted this one on a sheet of plexiglass to keep the counter board's ground isolated from the radio's chassis.
This 1980 Madison radio's original clock was the mechanical type, and leaves a nice big hole on the metal chassis under the bezel. I tried mounting it on the front face of the metal panel, but parts of the plastic faceplate bezel interfered with it. Mounting it on the inside of the panel improved the clearance, but causes the digits to be set back from the window in the bezel more than I like. Some days you just have to compromise.
Fixing the digital-noise problem proved not too tricky. A 0.1uf disc cap from the counter ground to chassis ground, and a 330uH filter in the positive power lead took care of that. Had to extend the length of the negative power wire and hook it to the big filter's ground on the radio's pc board. The positive side is tapped off the power switch.
I neglected to shoot a pic of the input hookup. It's the same as we use for the 6-digit version. A .001uf disc connects the input-coax shield to the pcb ground alongside the VCO test point. A 470-ohm 1/4W resistor is inserted between the radio's VCO test point and the center lead of the input coax.
I should have put the top cover on the radio before shooting this one. The smoked plex hides the ugly stuff pretty well that way. But stray room light makes all of it visible here.
There are some other oddball differences in how this counter operates. If you want all eight digits, you have to use a 1-second gate time. This means the display won't update until a full second after you turn the clarifier. Not a user-friendly feature. The PLJ8 display allows you to use a prescaler, or to set the gate time to 1/10th of a second. Or both. The 6-digit display updates roughly ten times per second, IIRC. The setup options on the 8-digit version allow this, and it's the best option as I see it. You only get 7 digits, but so what?
Your mileage may vary.
Most radios won't have a window wide enough for 8 digits anyway, but this one did.
Just goes to show that just because you can doesn't always mean you should.
73
Simple answer is you don't. 6 digits are plenty. But this customer wanted it, so here's what we found getting it installed.
There are a few differences between this one, the SanJian PLJ8-LED display and the 6-digit PLJ6-LED we normally use. Biggest difference besides the extra two digits is the voltage regulator. The 6-digit version has an analog regulator. This one uses a switchmode-type.
This increases the digital noise this thing generates, and we had some issues with "zing" noises in the receiver audio.
We mounted this one on a sheet of plexiglass to keep the counter board's ground isolated from the radio's chassis.
This 1980 Madison radio's original clock was the mechanical type, and leaves a nice big hole on the metal chassis under the bezel. I tried mounting it on the front face of the metal panel, but parts of the plastic faceplate bezel interfered with it. Mounting it on the inside of the panel improved the clearance, but causes the digits to be set back from the window in the bezel more than I like. Some days you just have to compromise.
Fixing the digital-noise problem proved not too tricky. A 0.1uf disc cap from the counter ground to chassis ground, and a 330uH filter in the positive power lead took care of that. Had to extend the length of the negative power wire and hook it to the big filter's ground on the radio's pc board. The positive side is tapped off the power switch.
I neglected to shoot a pic of the input hookup. It's the same as we use for the 6-digit version. A .001uf disc connects the input-coax shield to the pcb ground alongside the VCO test point. A 470-ohm 1/4W resistor is inserted between the radio's VCO test point and the center lead of the input coax.
I should have put the top cover on the radio before shooting this one. The smoked plex hides the ugly stuff pretty well that way. But stray room light makes all of it visible here.
There are some other oddball differences in how this counter operates. If you want all eight digits, you have to use a 1-second gate time. This means the display won't update until a full second after you turn the clarifier. Not a user-friendly feature. The PLJ8 display allows you to use a prescaler, or to set the gate time to 1/10th of a second. Or both. The 6-digit display updates roughly ten times per second, IIRC. The setup options on the 8-digit version allow this, and it's the best option as I see it. You only get 7 digits, but so what?
Your mileage may vary.
Most radios won't have a window wide enough for 8 digits anyway, but this one did.
Just goes to show that just because you can doesn't always mean you should.
73
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