The AM Forum

I did like to have a digital read-out for my HRO, R1155 etc without modifying the receiver. Si I bought the low cost programmable digital counter at Ali express, Epay etc. for a few bucks. The counter has a capacitor input that did allow me to put 5 Volts DC at the input via a 56 Ohm resistor and a ferrite beat. to power a remote RF amp to pick-up the RF from the LO of the receiver. The RF amp is nothing more than a J-FET to get a very high input impedance. The FET should be one that take approx 10 - 15 mA at zero gate volts, I used a BF245, but a J310 and alike should work fine. The drain goes via a thin coax to the counter, pic's attached. The counter performs perfectly and is programmed to subtract the 456 KHz IF.
Just left to make is a small case with power supply.

and the last pic

Sure beats the heck out of trying to read those little charts!!!  Terry

Nico,

I see those counters from China on Epay for less than 12 USD shipped (to USA). I can think of a few places I could use them around here. I'm going to add it to my "wish list".

If I understand correctly, you needed to add the amplifier just so you wouldn't need to make a direct connection to the receiver instead, relying on a "gimmick" capacitor. Well done.

Don

I've use them on the work bench to check reciever's lo by using a couple turns of hookup wire around the mixer tube. Also can use them to set the lo w/o using a signal generator.

Terry

Hi Don.
The counters indeed are less than 12 $. And they are real easy to program for IF offset, gate time etc. The amp is more to be able to enter the signal through a thin coax cable and remain a VERY loose coupling with the oscillator indeed without a physical connection.  So it transforms the very high impedance to a current source to drive 50 Ohms.

Cool. I could watch my SX-28 drift with that!

What radio is that on your work bench Terry?. I have a nice collection of radio's from 1926 to 1938. Love to restore them.

Hi Nico
It a big old Philco 41-300.
Here's technical stuff:  http://www.nostalgiaair.org/Resources/423/M0013423.htm
Great sounding set w/push pull 42's in the output and - feedback.
 
Terry

Nice job Nico!

What is the value of the gate resistor?

I used 470 kOhm, but non critical.

Nice radio Terry, not only technical, but also for decoration.
Here is an other interesting radio, a Manufrance BA36 from 1936 Tone control by bandwidth change of the IF, Balanced detector (+ and - output) and each leg driving balanced preamp using 2 EF6 tubes and balanced output amp with EL2. Balancing is assured more by common cathode resistors.
But my favorite is a 1926 radio, pics attached. It looks new, also the tubes are new, quite unbelievable. Such a find is quite rare.

diagram of the detector and output of the manufrance