Picked up a Sunn 200S head that does not turn on. 2 amp fuse was blown, these should have a 3 amp fuse. Looking inside I found a solid state rectification mod. Primary and secondary at the PT seem okay. The secondary 5V tap is not in use and taped off.
I also found filter caps in series pairs. The first series pair are 220 uF 350V. Schematic calls for 30 uF 525V. In series the effective capacitance would be 110 uF. Does the voltage handling double to 700V? Is this cap value okay here?
I also found that the connection between the two series caps was broken. The second cap lead wire broke off. I tried to solder a new wire onto it but I cannot get the solder to stay there.
Before discovering this disconnect at the first series pair, I brought the unit up slowly on the variac and bulb limiter. The bulb got brighter as I turned it up and stayed lit. At full voltage the entire amp was drawing about 1.5 amps. This was in standby mode. No tubes installed. I measured only 14 VDC at the standby switch. I was expecting 500 VDC. As I write this I am wondering if I have the full 120 VAC at the primary. Although I did see very little resistance (about 2 ohms) across the PT primary.
I am seeing about 60 ohms between the high voltage secondary windings, and about 30 ohms each wire to the center tap.
I next plan to clip in some appropriate cap where the first series pair is disconnected and test VDC again at the standby switch.
Before I do I was hoping for some feedback. Thank you, MC
I also found filter caps in series pairs. The first series pair are 220 uF 350V. Schematic calls for 30 uF 525V. In series the effective capacitance would be 110 uF. Does the voltage handling double to 700V? Is this cap value okay here?
I also found that the connection between the two series caps was broken. The second cap lead wire broke off. I tried to solder a new wire onto it but I cannot get the solder to stay there.
Before discovering this disconnect at the first series pair, I brought the unit up slowly on the variac and bulb limiter. The bulb got brighter as I turned it up and stayed lit. At full voltage the entire amp was drawing about 1.5 amps. This was in standby mode. No tubes installed. I measured only 14 VDC at the standby switch. I was expecting 500 VDC. As I write this I am wondering if I have the full 120 VAC at the primary. Although I did see very little resistance (about 2 ohms) across the PT primary.
I am seeing about 60 ohms between the high voltage secondary windings, and about 30 ohms each wire to the center tap.
I next plan to clip in some appropriate cap where the first series pair is disconnected and test VDC again at the standby switch.
Before I do I was hoping for some feedback. Thank you, MC
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