How does it Work?

 

(1) Mixer

(2) IF amp and BFO

(3) Detector

(4) Audio Amp

(5) Power Supply

 

 

From the "Mixer", we move on to the IF amp. First notice at the output of the mixer tube is a 455 kc IF transformer (T2) This transformer has two arrows. One going up, and the other going down. This means that there are two coil slugs inside the core. One slug tunes the output filter circuit from the "Mixer" and the other slug tunes the " 455 input filter circuit" which is fed into the control grid of the First IF amp through pin #1 of the 6BZ6.

The output of this tube (the "plate") is then fed through another IF transformer (T3). It too has two slugs. The 455 signal then goes into the control grid of the second IF amp tube 6U8. The output of this tube then goes into yet another IF transformer (T4). Yes, it too has two slugs as well. The output is then taken to the diode detector circuit which will be discussed in the next section.

As you can see, this IF amp circuit consists of two amps that are "Inductively" transformer coupled together. This is important because during the alignment procedure, you will have to tune all of them for peak performance on 455. This consists of simply peaking each section by "tweaking" the coil slugs with your magic coil tool.

One additional thing to note is the "RF Gain" control on the first IF amp tube (6BZ6). Pot R5 can be used to control the gain of this tube. If you come across a strong signal, chances are pretty good it will overload this IF tube causing distortion. Simply reduce the gain by increasing the B+ Voltage to the cathode.


We also have a BFO (Beat Frequency Oscillator). This is another "mini-transmitter" that generates a signal just above or just below the 455 IF frequency. Again, like the mixer, this signal beats against the 455 signal and produces a pleasant audio tone which makes copying CW signals easy. It also helps demodulate single side band (SSB) signals. The thing to note about this circuit is that it can be turned on and off. Simply switch the ground of the switch to pin 8 of the other half of the 6U8 to complete the cathode circuit. Like the IF amp, this oscillator is also transformer coupled to the IF amps. One side of the transformer set's the 455 frequency of the oscillator. The other side controls the amount of signal inject into the IF amp. Too much and the other IF signal are covered up. Too little and SSB is not demodulated and CW signal tones will drop or disappear altogether. Setting the level is somewhat critical and you want to compromise on setting just enough to copy weak signals as well as the strong ones.

 

(1) Mixer

(2) IF amp and BFO

(3) Detector

(4) Audio Amp

(5) Power Supply



Complete Schematic for the Conar Model 500 Receiver

Conar Transmitter Manual - and - Conar Receiver Manual