Replacing all the caps is an EXPENSIVE proposition. There is nothing "fad" about this. It is physics. Please go visit the OEM web sites and look at the specs. They are quite conservative, showing desegregation in as little as three years in correct use. Faster if abused ( storage on the top bay in a warehouse, next to a hot resistor, too much current etc.) Back in my Failure Analysis lab days, we found seven years about where it becomes significant. Not talking failures, just decrease in capacitance, higher ESR, worsening of DF and DC leakage.
As Nanoo says, reaping is not to be used as shotgunning for an unidentified fault. It is maintenance. If you have a fault, fix that first. The good news in modern caps generally are of higher quality than 20 year old ones.
As Nanoo says, reaping is not to be used as shotgunning for an unidentified fault. It is maintenance. If you have a fault, fix that first. The good news in modern caps generally are of higher quality than 20 year old ones.
Everyone has great answers for you. But hearing noises during start up usually means its the power supply electrolytics. Replace these first, then clean out all your pots and switches (I use CRC 2-26). Then check any other electrolytic in the circuit and slowly replace them. Iwouldn't go as far as replacing the heatsinks and compound until all else fails Normally you can tell from the pitch of the sound what the problem is.
Recapping can almost never fix a faulty amp. It is done as a preventative measure, and for a potential (but unlikely) sonic upgrade - not to repair.
Replacing thermal compound can never fix a faulty amp (it is also totally unnecessary unless you have a visibly super crispy, burnt class A amplifier).
Bad solder joints are really rare (but I suppose they do show up occasionally, although I've only experienced it once in the many amps I've worked on).
Cleaning all the controls can - and will - fix almost every vintage amp with problems. I've had several amps behave exactly as you say: strange noises or weak sound directly after power-on (even without touching anything), only for it to settle after a little while. Cleaning the switches and potentiometers has fixed that - every time.
Bad small signal transistors in the pre amp are also a common problem, with similar symptoms. There are even some types that are almost always defective.
Finally, remember this: when experiencing problems, you must always clean all controls and switches before attempting anything else whatsoever. I've wasted so much time trying to track down bizarre unsolvable problems, only for it to be a dirty tape monitor switch.
Replacing thermal compound can never fix a faulty amp (it is also totally unnecessary unless you have a visibly super crispy, burnt class A amplifier).
Bad solder joints are really rare (but I suppose they do show up occasionally, although I've only experienced it once in the many amps I've worked on).
Cleaning all the controls can - and will - fix almost every vintage amp with problems. I've had several amps behave exactly as you say: strange noises or weak sound directly after power-on (even without touching anything), only for it to settle after a little while. Cleaning the switches and potentiometers has fixed that - every time.
Bad small signal transistors in the pre amp are also a common problem, with similar symptoms. There are even some types that are almost always defective.
Finally, remember this: when experiencing problems, you must always clean all controls and switches before attempting anything else whatsoever. I've wasted so much time trying to track down bizarre unsolvable problems, only for it to be a dirty tape monitor switch.
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I second the last two posts, but let me add a couple things to the heat sink topic. If it is an older design with TO-3 type packages where the current goes through the hardware stack, and even worse, if the board is in the stack, these connections can degrade over time and cause all kinds of problems. Getting current through a TO-3 package reliably is actually very hard. Check to be sure the nuts are snug and look for any signs of overheating.
On white thermal compound, what happens is over time, the thermal conductive particles pump their way out from under the transistor and form a ring around the outside, leaving only the oil to do the job. Sil-pads may not have as good "as installed" transfer, but they stay the same forever. They don't collect a layer of insulating dust either.
Back in my old Failure Analysis Lab days, we banned the hardware stack as a current path redesigning things with lugs soldered to the board under the stack and used a set of bevel washers to act as springs in the stack. Star washers were totally banned from all our products. I also saw to it to ban mica-paste in favor of sil-pads or graphite pads. These changes did wonders for our reliability.
On white thermal compound, what happens is over time, the thermal conductive particles pump their way out from under the transistor and form a ring around the outside, leaving only the oil to do the job. Sil-pads may not have as good "as installed" transfer, but they stay the same forever. They don't collect a layer of insulating dust either.
Back in my old Failure Analysis Lab days, we banned the hardware stack as a current path redesigning things with lugs soldered to the board under the stack and used a set of bevel washers to act as springs in the stack. Star washers were totally banned from all our products. I also saw to it to ban mica-paste in favor of sil-pads or graphite pads. These changes did wonders for our reliability.
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Interesting about the star washers and beryllium compound reliability results, tvr geek. I just replaced 20 blown TO3 output transistors in a 1994 Peavey product, and thought adding stainless star washers would be big improvement between the mount nuts and the ground trace on the PWB.
I won't say crackling can't be controls, solder joints, or transistors BUT I've improved sound and feature performance of the following gear in the last 3 years by replacing all the electrolytic caps 1. 1976 Reader's Digest FM radio (Japan) 2.1961 Dynaco ST70 amp (plus output tubes) 3. 1968 Hammond H182 organ (71 caps, 1 tube socket, no tubes) .
The Peavey amp needed 107 other parts due to OT blow up, but I replaced the caps as a matter of course due to the calender. I learned this practice from the MacIntosh salesmen in 1970 when my 1961 build ST70 amp was putting out 14 watts at 2% HD. New caps, rectifier and output tubes, the next year it was putting out 70 watts at 1% HD. Caps first, then measure wattage (improved), then rectifier tube (another improvement), then measure, then output tubes (up to stock wattage). As far as solid state stuff, Sakis in his "vintage amp repair thread" suggest replacing all e-caps in out of warrenty equipment as a matter of course. I had to quit using my Sony TC250 deck as a preamp, because even after I replaced the power cap pair, the sound was fuzzy and indistinct, and there were >100 other electrolytic caps in there. Oh, I've fixed a PCAT mainboard, a Pentium 4 from about 98, with all new e-caps. Also a computer hard disk drive. computers are full of really vile life rating electrolytic caps.
I won't say crackling can't be controls, solder joints, or transistors BUT I've improved sound and feature performance of the following gear in the last 3 years by replacing all the electrolytic caps 1. 1976 Reader's Digest FM radio (Japan) 2.1961 Dynaco ST70 amp (plus output tubes) 3. 1968 Hammond H182 organ (71 caps, 1 tube socket, no tubes) .
The Peavey amp needed 107 other parts due to OT blow up, but I replaced the caps as a matter of course due to the calender. I learned this practice from the MacIntosh salesmen in 1970 when my 1961 build ST70 amp was putting out 14 watts at 2% HD. New caps, rectifier and output tubes, the next year it was putting out 70 watts at 1% HD. Caps first, then measure wattage (improved), then rectifier tube (another improvement), then measure, then output tubes (up to stock wattage). As far as solid state stuff, Sakis in his "vintage amp repair thread" suggest replacing all e-caps in out of warrenty equipment as a matter of course. I had to quit using my Sony TC250 deck as a preamp, because even after I replaced the power cap pair, the sound was fuzzy and indistinct, and there were >100 other electrolytic caps in there. Oh, I've fixed a PCAT mainboard, a Pentium 4 from about 98, with all new e-caps. Also a computer hard disk drive. computers are full of really vile life rating electrolytic caps.
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