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Old 5th Dec 2017, 1:16 am   #5
Boater Sam
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Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
Default Re: DAC 90A Smoothing Capacitor replacement

You can check the resistors as you go replacing capacitors, BUT bear in mind that you may need to lift one end to avoid an incorrect reading due to a parallel resistance, often studying the circuit will tell you.
I would be surprised if any are too far out of spec, most were only 20% tolerance and are not critical. The most critical are any high value eg. over 1M ohms which tend to go high and any cathode bias resistors to chassis which will be low values and take a bit of current.
Restuffing the smoothing can is my prefered method if need be, cut around the bottom where the clamp sits then it doesn't show when refitted. I keeps it looking neat rather than a hemorrhoid underneath. With modern smaller capacitors there is plenty of room in the can for 2, wrap in plastic to insulate and bring the negative wires out to one chassis connection, don't try to connect to the can, its alluminium.
Valves will likely be OK, UL41 is the hardest worked and prone to drawing grid current due to debris on the inside of the base button. Leads to over-running and audio humming which is not due to the smoothing capacitor. Sometimes this can be flashed off, search under "UL41 valves recovery" "sparking UL41" etc. will give you some ideas.
Long wave not working, could be switch contacts, frame aerial wire disconnected, oscillator coil. Look for components and connections that are only used on long wave.
Agreed, its a pleasure to help someone who starts out correctly and has provided all the relevant info at the outset.
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