The BUSH AC 91 DAC 90
DAC 90A DAC10. Repairs to The Nations favourite.
I include all the models as they are all basically the same design. With similar
common faults. The early sets had Octal valves fitted. The AC91 has a mains
auto transformer, and a short waveband. The DAC 10 has a preset tuned button
selector.
It is no wonder they are the nations favourite,
once all the common faults have been corrected, they work so well. The bakelite
cabinets, with a little elbow grease and a dab of T CUT, ( Car body restorer.
) will shine like new. Most of the spare parts can be obtained, as the sets
are so common. Safety standards in the 40s and 50s were very basic. Great
care must be taken when using these AC/DC sets as the chassis can be live.
If these sets were modified to conform to today's modern standards, the set's
historical value would be ruined. So to improve safety, I connect these type
of sets to the power via a R.C.D. This gadget will cut off the supply if there
is a mains leak to earth.
First thing to do with these models, prior to working on the set, the chassis must be completely dried out. Pop the chassis in the airing cupboard for a few days, this is important as one of the components that cannot be replaced is the Wavechange switch. If H.T. is applied to it, and the slightest leak occurs across the paxolin construction, it will spell disaster. After dismantling and going through the usual cold checks and fault finding. The Troublesome paper capacitors have to be changed, about 15 in all. The electrolytic smoothing capacitors, after 50 years will almost certainly need replacement. The best way to do this is remove the can from the chassis, cut off the end with a junior hacksaw. carefully heat the can until the pitch melts, this holds the contents in the can. The whole lot can now slide out. There is plenty of room in the can to fit 2 modern replacements. secure them with car body filler and refit the old cut off end end cap. When all the new parts have been installed. A general clean up is always necessary. Take great care of the tuning scale. The painted lettering on the glass can get very fragile over time, and just a very gentle dust off with a very soft brush is adequate. If too much force is used the lettering can completely rub off!!! ruining the set.
See the end cap, cut off as neatly as possible.
After heating, the contents of the can slides out. Plenty of room to fit replacements.
See the new capacitors fitted, and the can ready to be sealed up.
A common problem with all the DAC 90 models is that the top right hand of the back covers becomes very brittle and crumble away, this is caused by the heat dissipated by the dropping resistor mounted nearby. For safety reasons the set should not be used in this condition. A good method of restoring the back, is to repair the damage with G.R.P. see below the back plate tapred and sanded so layers of fiberglass can be bonded on.
next layer up some suitable GRP woven mat to the original thickness of the back plate.
Cut and trim to size using a paper template and a fine bladed jig saw. Looking good now, and ready for painting. Using Matt black spray paint, The completed back looks fine.
