Re: hph's 55 Clipper Project
Posted by humanpotatohybrid On 2023/12/25 22:08:11
I decided to test the capacitance of the paper caps. The capacitor number is followed by the rated μF value (±10% tolerance) then the actual value. As you can see, all the capacitors are defective but interestingly they are above their rated value.
C17 0.47, 0.772
C16 0.47, 2.97
C5 0.05, 0.11
C15 0.007, 0.012
C12 0.1, 0.308
C10 0.002, 0.0032
C8 0.01, 0.017
C11 0.003, 0.0052
C2 0.05, 0.19
I also tested the triple electrolytic, which had values of 30, 32, and 33 μF (supposed to be 20 for all).
To be honest, since all the capacitors seemed to be gaining capacitance, probably the set would have worked fine, but there's not much of a way to be sure of that without testing them. In addition, excessive capacitance in capacitors like C10 and C11 could cause weak treble response, especially at low listening volumes. It's also possible the caps were failing in other ways, for example having an excessive ESR. I don't have a fancy capacitor tester so can't test for this.
The situation is somewhat analogous to firing up an old engine on something like 20W50 oil. It's reasonable to expect that you would have high oil pressure, but you have to trust/assume that the oil pump even works! Until you inspect the pump and hook up an oil gauge, there's no way to be certain that you will have what you may expect. Likewise, even though our capacitors held at least their rated capacitance, there's no guarantee that they would have without testing them, and the excess capacitance is not necessarily preferable. In many of the applications, the design capacitance is optimal. And to be clear, just the process to test the caps in situ is nearly the same difficulty to just replace them.
The cost of the replacement caps was around $30 including shipping but I ordered more than I needed so I had some spares for mistakes or future projects. Needed to replace the RF amp tube also, about $10.
Attach file:
20231225_211600.jpg (8,006.09 KB)
C17 0.47, 0.772
C16 0.47, 2.97
C5 0.05, 0.11
C15 0.007, 0.012
C12 0.1, 0.308
C10 0.002, 0.0032
C8 0.01, 0.017
C11 0.003, 0.0052
C2 0.05, 0.19
I also tested the triple electrolytic, which had values of 30, 32, and 33 μF (supposed to be 20 for all).
To be honest, since all the capacitors seemed to be gaining capacitance, probably the set would have worked fine, but there's not much of a way to be sure of that without testing them. In addition, excessive capacitance in capacitors like C10 and C11 could cause weak treble response, especially at low listening volumes. It's also possible the caps were failing in other ways, for example having an excessive ESR. I don't have a fancy capacitor tester so can't test for this.
The situation is somewhat analogous to firing up an old engine on something like 20W50 oil. It's reasonable to expect that you would have high oil pressure, but you have to trust/assume that the oil pump even works! Until you inspect the pump and hook up an oil gauge, there's no way to be certain that you will have what you may expect. Likewise, even though our capacitors held at least their rated capacitance, there's no guarantee that they would have without testing them, and the excess capacitance is not necessarily preferable. In many of the applications, the design capacitance is optimal. And to be clear, just the process to test the caps in situ is nearly the same difficulty to just replace them.
The cost of the replacement caps was around $30 including shipping but I ordered more than I needed so I had some spares for mistakes or future projects. Needed to replace the RF amp tube also, about $10.
Attach file:
20231225_211600.jpg (8,006.09 KB)
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