kvflyer
Super Member
-- This is a rebroadcast of a thread that I did long ago on the Antique Radio Forum website. When they did an upgrade, a lot of stuff disappeared. So I hope it helps. For those who are familiar with this, nothing new. --
Several members have asked about rebuilding electrolytic capacitors. What I prefer to work on is HH Scott amplifiers. I just like the way that they are built and sound. I also have excellent results with a restoration or for that matter, just to get one going. As you all know, the electrolytic capacitors are rather old, between 40 and 50 years old. The capacitors were never designed to last that long. However, some still survive. I will not be a hypocrite and tell you that every amplifier, tuner or receiver that I own have new electrolytic caps. They do not. But I carefully monitor the operation of them by sound (ears!) and feel (touch). They should never get warm unless heated by radiated heat from the tubes. What I want to show you is my approach to this issue. This is not the only way or the best way to go. It is the way that I have chosen to go because of pride in the accomplishment and frugality. I can rebuild a can for less than $10 and frankly, it is fun. Please realize that these pictures are not all of the same capacitor. I have done several caps and this is a compilation of photos. But you get the idea. First is the un-crimping of the aluminum can lip. This is dangerous and requires much care if you choose use this method. Always point the blade away from you; never hold the cap in your hand. I start by getting the blade under the crimped aluminum and working it gently up.
I continue to raise the lip with the small screwdriver. (For those of you who worked for the Bell System, this was referred to as a dial screwdriver
).
Here is a picture of the dial screwdriver. It is robust and has a fat handle. Works very well and is good for removing set screws from knobs too. Displayed next to an AUD $10 bill for size.
After I get enough of the aluminum pried up, I use a pair of duck billed pliers to straighten the aluminum slightly. This allows the steel ring and "guts" to come out more easily.
Next, we heat the outside of the can with a heat gun. Mine is a paint stripper gun but you could borrow your partner's hair dryer. Just remember to put it back where you found it or you will hear about it. (Look closely in the background and you may see an adult bevy. Obviously, this picture was taken in the evening!)
Next, we see the insides of the can pulled out. Sometimes this is easy, sometimes it is a bear. I use welder's gloves to hold the heated can and pull the guts out carefully. You don't want to pull the lug out of the fiber disc.
Here are the new electrolytic capacitors that will be inside of the can. They are much smaller and after searching the vendors' website, I found what I needed. **Note** Please keep in mind that if you are repairing the bias bridge capacitor of a Scott (or other brand) amplifier that the common lead will be Positive (+) as opposed the the more familiar negative (-). Do this incorrectly and you will be rewarded with destroyed new capacitors or even worse!!! It is a good idea to use 105˚C rated capacitors for increased reliability. You can use capacitors that are rated higher voltage. But I would not deviate much from the original value. For instance, if the original capacitor was a 50µFD value, the standard today would be 47µFD. Likewise if the value was 20µFD, the standard value to use is 22V.
After I have the components mounted on the phenolic wafer and soldered to the lugs, I start by rolling the edge that I had pried up on the face of my cast iron vice. I roll back and forth and eventually most of the aluminum folds back over the wafer.
After it is rolled as much as possible, I use a small light weight tack hammer to work my way around the edge carefully. I do this slowly because the aluminum is stretched and wants to bunch up. If I am patient, it smooths back down after going around the edge a couple of times.
Notice that there is a very small hold drilled next to the terminal for the leads of the new capacitors to pass through. Those leads are then just soldered to the existing lug. For the ground lug, you may have to use a very small file and make a groove in the phenolic mounting washer to allow the common lead to pass through the small opening.
Over the years, I have accumulated a few NOS "FP" or "Twistlock" style capacitors. I cut them open and use the new, untwisted steel mounting ring. Most of the time when you try to get the old capacitor out, those tabs will snap off or become seriously compromised. Having a new one helps. I have noticed that there is much interchangeability between the different brands.
Several members have asked about rebuilding electrolytic capacitors. What I prefer to work on is HH Scott amplifiers. I just like the way that they are built and sound. I also have excellent results with a restoration or for that matter, just to get one going. As you all know, the electrolytic capacitors are rather old, between 40 and 50 years old. The capacitors were never designed to last that long. However, some still survive. I will not be a hypocrite and tell you that every amplifier, tuner or receiver that I own have new electrolytic caps. They do not. But I carefully monitor the operation of them by sound (ears!) and feel (touch). They should never get warm unless heated by radiated heat from the tubes. What I want to show you is my approach to this issue. This is not the only way or the best way to go. It is the way that I have chosen to go because of pride in the accomplishment and frugality. I can rebuild a can for less than $10 and frankly, it is fun. Please realize that these pictures are not all of the same capacitor. I have done several caps and this is a compilation of photos. But you get the idea. First is the un-crimping of the aluminum can lip. This is dangerous and requires much care if you choose use this method. Always point the blade away from you; never hold the cap in your hand. I start by getting the blade under the crimped aluminum and working it gently up.
I continue to raise the lip with the small screwdriver. (For those of you who worked for the Bell System, this was referred to as a dial screwdriver
).
Here is a picture of the dial screwdriver. It is robust and has a fat handle. Works very well and is good for removing set screws from knobs too. Displayed next to an AUD $10 bill for size.
After I get enough of the aluminum pried up, I use a pair of duck billed pliers to straighten the aluminum slightly. This allows the steel ring and "guts" to come out more easily.
Next, we heat the outside of the can with a heat gun. Mine is a paint stripper gun but you could borrow your partner's hair dryer. Just remember to put it back where you found it or you will hear about it. (Look closely in the background and you may see an adult bevy. Obviously, this picture was taken in the evening!)
Next, we see the insides of the can pulled out. Sometimes this is easy, sometimes it is a bear. I use welder's gloves to hold the heated can and pull the guts out carefully. You don't want to pull the lug out of the fiber disc.
Here are the new electrolytic capacitors that will be inside of the can. They are much smaller and after searching the vendors' website, I found what I needed. **Note** Please keep in mind that if you are repairing the bias bridge capacitor of a Scott (or other brand) amplifier that the common lead will be Positive (+) as opposed the the more familiar negative (-). Do this incorrectly and you will be rewarded with destroyed new capacitors or even worse!!! It is a good idea to use 105˚C rated capacitors for increased reliability. You can use capacitors that are rated higher voltage. But I would not deviate much from the original value. For instance, if the original capacitor was a 50µFD value, the standard today would be 47µFD. Likewise if the value was 20µFD, the standard value to use is 22V.
After I have the components mounted on the phenolic wafer and soldered to the lugs, I start by rolling the edge that I had pried up on the face of my cast iron vice. I roll back and forth and eventually most of the aluminum folds back over the wafer.
Notice that there is a very small hold drilled next to the terminal for the leads of the new capacitors to pass through. Those leads are then just soldered to the existing lug. For the ground lug, you may have to use a very small file and make a groove in the phenolic mounting washer to allow the common lead to pass through the small opening.
Over the years, I have accumulated a few NOS "FP" or "Twistlock" style capacitors. I cut them open and use the new, untwisted steel mounting ring. Most of the time when you try to get the old capacitor out, those tabs will snap off or become seriously compromised. Having a new one helps. I have noticed that there is much interchangeability between the different brands.
