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  • #3161
    Gerry O’Hara

    This Westinghouse Model W-1156-X was a top of the line set in its day. This imposing floor model sports a 9-tube line-up, including an RF stage, a push-pull audio output stage, bass and treble tone controls, a dual-cone 10 inch speaker in an infinite-baffle cabinet, push-button, motorized ‘automatic’ tuning and a ‘magic-eye’ tuning indicator – quite an impressive specification.

    The cabinet was dusty, but otherwise in good shape, warranting minimal work to restore it to its former glory – some minor scratches need toning-in with touch-up markers and then a polish with ‘Howards’ was sufficient to restore the original deep lustre of the veneer finish. A small patch of veneer was missing from the lower-most horizontal speaker rib, but as it would entail significant effort to replace and tone in/refinish as the rest of the cabinet, and even then, likely still a visible repair unless the entire cabinet was re-finished, , it was left as part of the ‘patina’ of this 72 year-old set (1939/40 model year).

    The chassis was found to be a 25Hz model, made for the Ontario market, thus having a large power transformer. Some corrosion on the upper side of the chassis was noted, but the underside, being enclosed with a tight-fitting base plate was in very good condition. Some evidence of earlier repairs were noted, eg. the two 0.005uF capacitors in the output stage anode circuits had been replaced, likely in the late-1950’s/1960’s. Other than that the set looked all-original.

    Chassis restoration comprised replacing all 23 wax/paper capacitors and four electrolytics, including one 200uF 100vw non-polarized electrolytic unit in the motor drive circuit. Resistors were checked and generally appeared to be within tolerance, so were left in place, with the exception of one that was out of tolerance. When function tested, it was noted that the magic eye tube (a 6U5) was very weak and the audio faded out after the set had been running for a few minutes – this was traced to a faulty 6F6 in the output stage (grid secondary emission issue). The 6SF5 audio driver tube was also found to be weak and replaced. Altogether fairly straightforward… until it came to working on the pushbutton tuning mechanism.

    The pushbutton tuning in this model is an electromechanical system that (like similar such systems) is prone to wear with age – but lets face it, they did not build it to last over 70 years! The system is simple in operation: the (reversible) motor derives its power through a pushbutton and a corresponding spring-loaded contact pin through a contact plate that rotates on the rear of the tuning capacitor gang. This plate comprises two semicircular brass plates separated by a phenolic insulating strip. At one end, this insulating strip is specially shaped with a ridge in the centre that the spring-loaded contact sits on when the pre-set station is tuned-in. The brass plates either side of this part of the insulation strip are bevelled to allow the contact to clear the conducting part of the disc when it is sitting on the insulating strip ridge. Each of the brass plates is connected to the opposite winding of the motor. Thus, if the contact pin corresponding to the pressed pushbutton is on one plate, the motor rotates in the appropriate direction until the contact is above the insulating strip, thus cutting off power to the motor which stops. If the contact pin is on the other plate, the motor will rotate in the opposite direction until it reaches the insulation strip. The location of the contact pins is set by tuning in the desired station, then holding in the manual tuning button plus the pre-set button that you want the station to be set on and a light (at the rear of the chassis) comes on. The contact pin corresponding to the selected button is then rotated around the contact plate in its slotted mounting plate until the light extinguishes, indicating correct setting for that station. The contact pins are arranged in two rows (inner and outer) to allow stations close together on the dial to be preset. The circuit mutes the detector during the tuning action so other stations are not heard while the tuning capacitor is being rotated.

    I found that even after careful cleaning and adjustment, I could only get the set working on four of the pushbuttons (numbers 2, 4, 6 and 8), corresponding to the contact pins on the inner set of contacts. Examination of the contact plate revealed that the ridge on the insulation strip corresponding to the outer set of contacts was well-worn and did not allow full insulation of the contact – this caused the tuning motor to ‘dither’ back and forth instead of stopping at the preset station. It was also noted that the bevelled edges of the brass plates was also worn and pitted either side of the insulation strip. The only recourse was to remove the contact plate and re-configure the insulation strip. This was possible as the insulation ridge was intact further in from where the contacts passed over it. This entailed cutting the insulation strip, turning the part with the ridge present around and re-attaching (with brass aircraft brake rivets) to the brass plates. This was done at the opposite side of the plates and the edge of the plates now against this section of the insulation strip bevelled to mimic the original machined edges on the other side of the plate. These efforts worked and all eight pre-set pushbuttons were successfully returned to service.

    The set was checked for alignment and only needed a slight tweak on the 19M bandspread range – all other ranges were found to be accurate and pulling in many stations. The dial was cleaned and knobs/acrylic dial glass cleaned with Novus #2 polish.

    The finished set looks a treat and works really well – the audio is very powerful with tight bass and crisp treble. A fine example of domestic AM radio design at its peak and the motorized tuning is great to watch in action.

    Bob Masse
    Forum Participant

    Nice job Gerry! It must of took a lot of perseverance to get the push button tuning working. I like how you saved the original finish.

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