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RESTORING A COSSOR  501AC  

WOOD  BAKELITE  CHASSIS  ETHICS  DIODE, TRIODE  TETRODE, PENTODE  STANDARDS PHOTOGUIDE  VIDEOS

PILOT  BUSH  EKCO  COSSOR  PHILCO  BAKELITE HISTORY VALVES DIODE, TRIODE  TETRODE, PENTODE  STANDARDS

 

Makers: A C Cossor Ltd. Approx. year of manufacture: 1949

Initial checks

Valve holders, switch noisy. Possible low HT line - power rectifier? Volume low even at full setting of control. Howls, instability. Suspect decoupling capacitors. Mains lead lethal.

The cabinet was filthy but intact. The output stage needed much work, including output valve replacement.

Chassis restoration in brief

The chassis top deck was vacuumed whilst still in cabinet before removing to complete. The knob attached to the tuning spindle was rusted solid and took patient work with WD40 to finally free and remove without damage. The chassis, once cleaned of the layers of dirt, proved to be in good general condition with only a small amount of rusting.

The (typically) very dangerous mains lead was replaced. A sleeved grommet was fitted to carry the new circular three-core cable through the chassis rear wall. I attached a self-tightening strap around the cable behind the exit point, leaving a little slack, to prevent inadvertent disconnection. A 13 A plug completed that side of the work.

The HT when tested was very low and was indeed due to a low-emission rectifier valve V5. This was replaced, bringing the HT up to a decent level but low volume and instability problems remained until the output valve V4 was replaced. This gave much improved volume and almost cleared the howling and instability.

A general clean up valve-holders, volume control, tone control, wave-change switch helped to further reduce the problem. To completely rid myself of the trouble, I replaced C27, 0.002 tone control circuit, the output valve cathode bias electrolytic C 30, 22, and 0.02 A F coupling C24. This last is marked on my circuit as a 0.005, but the one I removed and Im sure it was original was definitely a 0.05. Values in these A F circuits are not especially critical, though I would have thought the larger value was to be preferred in any case. (values are those quoted in the relevant Trader sheet)

The surface of the chassis was wire brushed to remove rust and an anti-rust compound was then applied. After this had dried the IF cans and the smoothing capacitor were polished then the chassis was masked off at the  valve-holders, aerial and loudspeaker socket strips. The control spindle nuts were loosened and the spindles taped to prevent paint adhering. The chassis was then painted with smooth Hammerite.

Cabinet Restoration

The loudspeaker frame and cone were carefully cleaned and the wooden panel carrying the badly stained and damaged loudspeaker grille fabric was stripped of the old and fresh fabric attached using spray adhesive. The cabinet itself was thoroughly degreased using foam cleanser, dried and brought up to a high sheen using metal polish.

The back panel with its frame aerial was cleaned by using a damp cloth and washing-up liquid.

 

PILOT  BUSH  EKCO  COSSOR  PHILCO

 

 

 

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