UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

kalee20 · 25th Aug 2008, 11:49 pm

Well, I've replaced most of the capacitors in a DAC90a this year.

THAT capacitor had already been replaced. Very soon after buying the radio (sold as working), the across-the-mains waxy failed. Snipping this and replacing the fuse restored operation, but I found the AVC capacitors measured a few megohms only of insulation resistance. The IF / RF cathode decouplers measured the same, and although this is non-critical, I figured that there must be moisture in there and in time, there would be internal electrolysis and the capacitance would eventually disappear. The tone corrector (0.01uF) measured 0.05uF at 100Hz, and smaller values at higher frequencies, so that went.

The wax-covered mica capacitors all measured OK - right capacitance, no leakage, so they could have stayed (I've replaced with polystyrenes or epoxy-dipped silver micas). The capacitors in the IFT's also stayed - the alignment was pretty bang on so I didn't suspect them. The HT electrolytic is OK so that stayed. And the 2-gang variable capacitor has also stayed.

The reasoning behind all this is, exactly as others feel above, when I put the radio back together I'd really like not to have to take it apart again for 10 years, so I want to do a good, permanent job.

25th Aug 2008, 11:49 pm	#11
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: "Change all capacitors...." Well, I've replaced most of the capacitors in a DAC90a this year. THAT capacitor had already been replaced. Very soon after buying the radio (sold as working), the across-the-mains waxy failed. Snipping this and replacing the fuse restored operation, but I found the AVC capacitors measured a few megohms only of insulation resistance. The IF / RF cathode decouplers measured the same, and although this is non-critical, I figured that there must be moisture in there and in time, there would be internal electrolysis and the capacitance would eventually disappear. The tone corrector (0.01uF) measured 0.05uF at 100Hz, and smaller values at higher frequencies, so that went. The wax-covered mica capacitors all measured OK - right capacitance, no leakage, so they could have stayed (I've replaced with polystyrenes or epoxy-dipped silver micas). The capacitors in the IFT's also stayed - the alignment was pretty bang on so I didn't suspect them. The HT electrolytic is OK so that stayed. And the 2-gang variable capacitor has also stayed. The reasoning behind all this is, exactly as others feel above, when I put the radio back together I'd really like not to have to take it apart again for 10 years, so I want to do a good, permanent job.