[dazzlevision]

Hello,

I had to replace a few more of those Erie PCB mount carbon composition resistors, due to split end caps.

The next step was the provision of a stereo decoder for the radio part of my Stereomaster. The correct unit is a BRC type SD1, which uses discrete component (PCB reference PC155). I do not have one but I do have a very similar unit from a Goodmans Module 80 stereo tuner-amplifier (made by Thorn/Ferguson), with PCB reference PC169.

Comparing the circuitry, the two units are of essentially the same design, but with a few component value variations:-

The series connected dc supply input dropper resistor is lowered in value due to the 24V Stereomaster supply, rather than 65V in the module 80.

The filter circuitry in the L and R channel detector stages and the coupling to the 19kHz doubler stage.

The “stereo radio” indicator lamp driver stage.

The input coupling low pass filter (from the FM detector).

Luckily, I have the service sheet for the Module 80 and the BRC Bulletin detailing the circuit and component changes in the Schedule B version of the BRC SD1 unit.

I made up a list of items to be changed in order to convert the Goodmans Module 80 PCB into a “Schedule B” (the “schedule” letter signifies changes made during production) BRC type SD1 unit. I had to replace one resistor with a wire link, remove one capacitor and change the values of several resistors and capacitors. I also had to replace a silicon transistor (Texas Instrument TIS91) with a germanium type in the stereo beacon lamp driver stage (Mullard AC128).

I then made up the wiring loom and B7G plug and soldered the free ends to the solder posts on the PC169/SD1 board. I was now ready to mount the unit onto the hardboard base, which already has a strip of wood with a rebate cut into it, for locating one end of the PCB. At the other end, there is a hole provided in the PCB which allows the fitting of 4BA countersunk screw, large flat washer, spacer, nut and shakeproof washer. I had to drill a 4BA clear hole on the hardboard base.

The next step was to plug in the B7G connector and switch on. I was rewarded with an illuminated stereo beacon and good stereo radio. I have a Philips VHF/FM multiplex stereo signal generator, which I haven’t used for years. I will connect it up at some point to see if the tuned circuits on the decoder board need adjusting.

Finally, I inserted a 2A (T) 20mm fuse (in an in-line fuse holder) into the secondary output wiring of the mains transformer (a factory production modification). I used a “Bulgin” type, which can be seen in the attached pictures.

The next step will be to refit the electronics into the cabinet and test it. After that, the mechanical overhaul, re-lubrication and adjustment of the BSR MA70 record deck.

To be continued……………..

Dazzlevision