Hi everyone. I'm new to the forum. I've been a vintage HiFi nut for 35 years or so. I've also been an Electronics Technician even longer. From reading through the various forums I am finding a common thread concerning certain practices in restoring vintage equipment which I would like to comment on.
It seems that most people here have an interest in keeping their HiFi stuff working properly, a hobby if you will. You can do this without spending a fortune. Check on the Internet and Google for the "US Navy NEETS" electronics course. Here it is:
http://www.rarmy.com/coleman/neets/
You can go as far as you want in this course and will give you an understanding of what's going on inside your stuff.
Next I suggest you find (Ebay) an inexpensive Oscilloscope. I perfer a dual trace with at least 20 MHZ bandwidth. You will also need two 10:1 probes to go with it. Some people make an USB adapter which will turn your computer into an O"scope and usually includes software so you can use your sound card as a signal generator. More elaborate software includes spectrum analyzer and distortion analyzer. The NEETS modules have a section on use of test equipment.
Get yourself a small multimeter. Some even have limited capacitance measurement capability. As you learn to use your O'scope you will find that you will end up using the meter to confirm shorts and opens.
A dummy speaker load is useful to check rated output. Using known resistance and voltage you can figure max power output in Watts. It's all part of the OHMs law circle of calculations. I found a pile of 50 watt 2 ohm resistors that allow me to hook up in various configurations for an output load . Make sure if you buy that they are resistive in nature and not inductive.
Check the internet for a video that will teach you how to solder.
Stock some tuner/contact cleaner. Deoxit is great. Component cooler will help you find thermal problems in circuits.
I'd like to weigh in on general "recapping" equipment. Most electrolytic caps are used for decoupling. It is the means to remove stray interference which affects circuit performance. Generally if your stuff is working don't fix it. In frequency sensitive devices such as tuners and tape recorders anytime you have components that are replaced alignment is in order. You may change the bias on your tape recorder even if you replace a cap of the same value. This change can also disturb the balance in stereo levels. One may now be higher that the other. Even brand new 20% tolerance in caps is not uncommon which leads to a wide variance in adjustment. Combine that with the aging coils in the recording heads and without proper alignment tapes and measuring equipment you could end up with a real mess. In my experience when I replaced caps in high end equipment I used a Sencore Z meter to check the cap for leakage and tolerance.
One set of caps that do get a lot of work is the DC filter caps in the power supply. Recap them? They can be expensive! Using the dummy load at full rated output and monitoring the plus and minus voltage supply rails with your O'scope you can see how well these caps are performing. If you see lots of (AC) ripple voltage riding on the DC or the rated voltage dropping quite a bit can point to other problems in the power supply such as the regulation. The money spent on power amps is proportional to the amount of design and care that went into the power supply of the amp. I've seen Mark Levinson amps where about 85% of the circuitry in the amp was in the power supply. They went to the great extent of not only regulating the DC voltage supply rails they regulated the AC input to keep it constant.
Keep this mind. This is just advise. You may not understand all I'm talking about or maybe all you want is to just keep your stuff working but don't want to work on it to the extent that you end up with a dedicated electronics shop. Just has anyone had this problem and how did you fix it? On the other hand I have had friends that have refurbished tube equipment where they wound their own transformers and used either cloth or clear plastic as insulation on wires because they figured that the carbon in the pigment of the insulation covering could affect sound quality. I've asked the same questions too. I have found that working on vintage stuff is more fun than the computerized equipment we have today, easier too. So have fun and ask lots of questions.
It seems that most people here have an interest in keeping their HiFi stuff working properly, a hobby if you will. You can do this without spending a fortune. Check on the Internet and Google for the "US Navy NEETS" electronics course. Here it is:
http://www.rarmy.com/coleman/neets/
You can go as far as you want in this course and will give you an understanding of what's going on inside your stuff.
Next I suggest you find (Ebay) an inexpensive Oscilloscope. I perfer a dual trace with at least 20 MHZ bandwidth. You will also need two 10:1 probes to go with it. Some people make an USB adapter which will turn your computer into an O"scope and usually includes software so you can use your sound card as a signal generator. More elaborate software includes spectrum analyzer and distortion analyzer. The NEETS modules have a section on use of test equipment.
Get yourself a small multimeter. Some even have limited capacitance measurement capability. As you learn to use your O'scope you will find that you will end up using the meter to confirm shorts and opens.
A dummy speaker load is useful to check rated output. Using known resistance and voltage you can figure max power output in Watts. It's all part of the OHMs law circle of calculations. I found a pile of 50 watt 2 ohm resistors that allow me to hook up in various configurations for an output load . Make sure if you buy that they are resistive in nature and not inductive.
Check the internet for a video that will teach you how to solder.
Stock some tuner/contact cleaner. Deoxit is great. Component cooler will help you find thermal problems in circuits.
I'd like to weigh in on general "recapping" equipment. Most electrolytic caps are used for decoupling. It is the means to remove stray interference which affects circuit performance. Generally if your stuff is working don't fix it. In frequency sensitive devices such as tuners and tape recorders anytime you have components that are replaced alignment is in order. You may change the bias on your tape recorder even if you replace a cap of the same value. This change can also disturb the balance in stereo levels. One may now be higher that the other. Even brand new 20% tolerance in caps is not uncommon which leads to a wide variance in adjustment. Combine that with the aging coils in the recording heads and without proper alignment tapes and measuring equipment you could end up with a real mess. In my experience when I replaced caps in high end equipment I used a Sencore Z meter to check the cap for leakage and tolerance.
One set of caps that do get a lot of work is the DC filter caps in the power supply. Recap them? They can be expensive! Using the dummy load at full rated output and monitoring the plus and minus voltage supply rails with your O'scope you can see how well these caps are performing. If you see lots of (AC) ripple voltage riding on the DC or the rated voltage dropping quite a bit can point to other problems in the power supply such as the regulation. The money spent on power amps is proportional to the amount of design and care that went into the power supply of the amp. I've seen Mark Levinson amps where about 85% of the circuitry in the amp was in the power supply. They went to the great extent of not only regulating the DC voltage supply rails they regulated the AC input to keep it constant.
Keep this mind. This is just advise. You may not understand all I'm talking about or maybe all you want is to just keep your stuff working but don't want to work on it to the extent that you end up with a dedicated electronics shop. Just has anyone had this problem and how did you fix it? On the other hand I have had friends that have refurbished tube equipment where they wound their own transformers and used either cloth or clear plastic as insulation on wires because they figured that the carbon in the pigment of the insulation covering could affect sound quality. I've asked the same questions too. I have found that working on vintage stuff is more fun than the computerized equipment we have today, easier too. So have fun and ask lots of questions.