The QUAD 50 is one of my favourite old bangers. It was manufactured until the 1980's, but has many features reminiscent of a bygone age. The topology is very like a typical valve amplifier. This one is a fairly early example and has a serial number in the 2000's. | |
The board is rather crusty, but nothing has exploded. These components are all original. | |
Internally looks fairly OK. Interesting that the capacitor is in great shape, very low ESR, no leakage, and plenty of microfarads. | |
The first problem found was a complete lack of direct volts. Two of these diodes in the bridge were open. | |
Fortunately the main transformer is working well, and no insulation problems were found. | |
A top view, the output transformer is connected to the front panel socket by ribbon. | |
Access to the octal socket for an input balun transformer. | |
Good quality transformer construction, the windings are well protected by this gunk. | |
Two new diodes in the bridge. | |
The first stage of board repair. Here I have replaced two very obviously faulty caps and tidied up the signal input connection. | |
A look under the back cover. The transistors and thermistor test OK, but a visual inspection is always a good idea. | |
Board repairs completed. Not as simple as I first thought. All the electrolytics and five of the transistors were replaced.
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Tested and adjusted, ready to go back together for a soak. | |
RT-Q50E pcb image
Price £12.50 with free p&p in UK.
£3.50 p&p for ROW.
I have designed a replacement PCB. Please get in touch if you have any interest.
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Click for schematic pdf.
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Click for schematic pdf.
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