03-23-2017, 07:57 AM
Lately I have been thinking (always a dangerous thing 
) and doing the caps a bit different.
I've tested the old caps I pulled out for years just for
Can't say I remember finding a bad paper foil cap. Even the ones that had been stored in hot places and most or all the bees wax sealing the ends had run out and made a mess. Still tested fine for cap and no leakage at stated WV. Same goes for the plastic enclosed paper foil even with the plastic cracked.
The electrolytics are different. Some good some bad. I got to thinking about the "standard" procedure of using a Variac to slowly bring up voltage to reform them. That is the "way" most of us have done it for years without ever thinking about it.
With rectifier tubes there is no DC to reform the caps till filament voltage get high enough for the tube to start conducting and then there is too much voltage available.
The radio posted above would OK for reforming caps with a Variac - solid state rectifiers.
Just did a 1946
Zenith AC/DC AM with 78 player.
Rectifier was a 35W4
Used a variable voltage DC supply to reform the 3 section cap. Several days at 5 or 10 volts then slowly over a day or so to section rating. Tubes were out and it was easy to pop 1 or 2 wires to test the cap. All 3 section were + 10 to 20% on capacitance and ESR was lower than new GP electrolytic.
The paper foil caps were replaced because all the bees wax had melted out. They were all 10 to 20% above cap rating and no leakage at rated WV. Note: Old caps were almost always over min cap rating.
Also finished up a Weston 981 Type 3. The old larger electrolytics same story, but in this case were replaced anyway. I am guessing the tube tester had been stored in a damp place and the Sprague orange cardboard / paper covers were mildewed and it is crowded in between the TBs. Modern GP caps are a LOT smaller and freed up a lot of room. There was a bad 25MF @ 25V - Cornell Dubilier (good brand) guessing it dried out. The red + end seal is HARD.
Cap testers have gotten CHEAP.
I am about to break into a Motorola communications test set. I expect to find most of the PS caps good like the last ones I did. Old habits die hard - I am planning on replacing the smaller caps like usual. Not worth reforming and testing to save a few pennies and traces on boards do not like to be desoldered too many times.
Just something to ponder
) and doing the caps a bit different.I've tested the old caps I pulled out for years just for
Can't say I remember finding a bad paper foil cap. Even the ones that had been stored in hot places and most or all the bees wax sealing the ends had run out and made a mess. Still tested fine for cap and no leakage at stated WV. Same goes for the plastic enclosed paper foil even with the plastic cracked.
The electrolytics are different. Some good some bad. I got to thinking about the "standard" procedure of using a Variac to slowly bring up voltage to reform them. That is the "way" most of us have done it for years without ever thinking about it.
With rectifier tubes there is no DC to reform the caps till filament voltage get high enough for the tube to start conducting and then there is too much voltage available.
The radio posted above would OK for reforming caps with a Variac - solid state rectifiers.
Just did a 1946
Zenith AC/DC AM with 78 player.Rectifier was a 35W4
Used a variable voltage DC supply to reform the 3 section cap. Several days at 5 or 10 volts then slowly over a day or so to section rating. Tubes were out and it was easy to pop 1 or 2 wires to test the cap. All 3 section were + 10 to 20% on capacitance and ESR was lower than new GP electrolytic.
The paper foil caps were replaced because all the bees wax had melted out. They were all 10 to 20% above cap rating and no leakage at rated WV. Note: Old caps were almost always over min cap rating.
Also finished up a Weston 981 Type 3. The old larger electrolytics same story, but in this case were replaced anyway. I am guessing the tube tester had been stored in a damp place and the Sprague orange cardboard / paper covers were mildewed and it is crowded in between the TBs. Modern GP caps are a LOT smaller and freed up a lot of room. There was a bad 25MF @ 25V - Cornell Dubilier (good brand) guessing it dried out. The red + end seal is HARD.
Cap testers have gotten CHEAP.
I am about to break into a Motorola communications test set. I expect to find most of the PS caps good like the last ones I did. Old habits die hard - I am planning on replacing the smaller caps like usual. Not worth reforming and testing to save a few pennies and traces on boards do not like to be desoldered too many times.
Just something to ponder
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