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HQ-145/Worth Recapping?
On Tue, 3 Jun 2008, Count Floyd wrote:
I have heard that there are very few electrolytic capacitors in this machine, as most of them are ceramic disk. The only ones are in a can on the chassis. If the radio is working well as original, would it be better to just leave well enough alone? I always try to live by the maxim: If it ain't broke..... Thanks, Of course, there were never many electrolytic capacitors in tube equipment. In the power supply, and bypassing the cathodes of the audio stages, and maybe at some point to bypass the B+ line close to the audio output stage. They weren't common because they weren't needed. Since tubes are high impedance, large value capacitors weren't needed much, and hence no shift to electrolytics. Solid state equipment uses a whole lot more electrolytics because of their low impedance operation, so you need large value capacitors for coupling and bypassing. Electrolytics are the only reasonable way to get those larger values. All the talk of recapping old radios is basically due to old capacitors. Badly designed capacitors at the time, or simply the best at the time, end up aging badly. The capacitors were fine at the time, it's just few gave much thought to the equipment being used decades past their prime. So decades later, those low value capacitors often need replacing because they just don't work properly nowadays. So you get bad bypassing at RF, and you get weak or non-existent audio because the coupling capacitors have gone. Replacing an electrolytic in the power supply is hardly "recapping", it's repair. "Recapping" is when someone feels they should replace all the capacitors, or actually needs to replace a specific capacitor. And then once you've done one, it often makes sense to do the whole lot, especially if it requires a complicated disassembly. IN some cases capacitors known to go bad over the decades were used, so it's worth replacing all of them because they will go bad eventually, or enough have gone bad that it's hard to get a handle on where the exact problem lies, and replacing the capacitors gets that variable out of the way. Michael VE2BVW |
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