I have not been doing any restorations for well over 3 months as I have been busy working on my radio display area.
I started on this strange looking record player before that, but then had a long pause whilst the above was going on and then again because I had to empty my radio workshop because the boiler people had to get the floorboards up to install the new boiler.
This record player is transistorised with a Garrard Autoslim record changer and a wood chassis enclosed in a plastic case. The amplifier circuit is based on the STC PC2. http://www.radiomuseum.org/r/kolsterbr_kp031.html
Manual available here. KB KP031 manual.
Previously I got as far as getting the amp partly working by replacing the leaky electrolytic caps. But it still had the strangest fault. It worked but it was pulsing loud and quiet and then after a while went quiet and stayed like that.
At this point I gave up and put it away to get on with the other things.
Yesterday I put it back on the bench and it was still doing the same up and down volume problem.
I eventually found it was caused by me having previously put C4, a 100uf cap in the wrong way round, this cap is decoupling the first stage transistor.
I adjusted the output stage bias, each OP transistor has to have a quiescent current of 3.5mA. There are 2 links which need to be un-soldered and I started by using just one ammeter in each "link" position in turn. This proved almost impossible to do as each of the 2 preset resistors effected the current in the other.
I finally gave up and found another ammeter and connected the each into Link a and link b as recommend in the manual, it was much easier.
The Garrard Auto slim record changer deck appeared that it had been serviced as all seemed to be free with fresh grease. Maybe I did it before, I cant remember now. When I tested the record deck the auto function would not work. There was still one part that was seized, the pawl on the change drive gear. Circled red
The top half (lid) of the plastic case is in reasonable condition
but the bottom half has suffered some damage possibly from sunlight or heat and the surface of the plastic has discoloured, pealed away and is crumbling and distorted.
I have attempted to reshape the plastic by warming with a hot air gun. The crumbling I have treated the best I can by rubbing super glue into the surface.
Now that has gone hard I will sand it smooth, fill some bad places and spray an even colour all over.
I will let you know how the restoration of the cabinet bottom goes.
Mike
I started on this strange looking record player before that, but then had a long pause whilst the above was going on and then again because I had to empty my radio workshop because the boiler people had to get the floorboards up to install the new boiler.
This record player is transistorised with a Garrard Autoslim record changer and a wood chassis enclosed in a plastic case. The amplifier circuit is based on the STC PC2. http://www.radiomuseum.org/r/kolsterbr_kp031.html
Manual available here. KB KP031 manual.
Previously I got as far as getting the amp partly working by replacing the leaky electrolytic caps. But it still had the strangest fault. It worked but it was pulsing loud and quiet and then after a while went quiet and stayed like that.
At this point I gave up and put it away to get on with the other things.
Yesterday I put it back on the bench and it was still doing the same up and down volume problem.
I eventually found it was caused by me having previously put C4, a 100uf cap in the wrong way round, this cap is decoupling the first stage transistor.
I adjusted the output stage bias, each OP transistor has to have a quiescent current of 3.5mA. There are 2 links which need to be un-soldered and I started by using just one ammeter in each "link" position in turn. This proved almost impossible to do as each of the 2 preset resistors effected the current in the other.
I finally gave up and found another ammeter and connected the each into Link a and link b as recommend in the manual, it was much easier.
The Garrard Auto slim record changer deck appeared that it had been serviced as all seemed to be free with fresh grease. Maybe I did it before, I cant remember now. When I tested the record deck the auto function would not work. There was still one part that was seized, the pawl on the change drive gear. Circled red
The top half (lid) of the plastic case is in reasonable condition
but the bottom half has suffered some damage possibly from sunlight or heat and the surface of the plastic has discoloured, pealed away and is crumbling and distorted.
I have attempted to reshape the plastic by warming with a hot air gun. The crumbling I have treated the best I can by rubbing super glue into the surface.
Now that has gone hard I will sand it smooth, fill some bad places and spray an even colour all over.
I will let you know how the restoration of the cabinet bottom goes.
Mike
