Ah, what AndrewT is suggesting is making a filtered power supply, using extra parts. While I dont mean to sound patronising, it sounds like this is above your current skill set.
I would stick with replacing the capacitors, as this along with your proposed change of volume pot, should restore the unit to it's as-new sound.
I would stick with replacing the capacitors, as this along with your proposed change of volume pot, should restore the unit to it's as-new sound.
Ah, more info. You are getting hum. Did it when new? If not, you don't need to mod, you need to repair.
If you don't understand exactly what Andrew said, I suggest you replace the main caps with modern high quality ones. You can probably go about twice as large and still not have problems with the lead spacing or height. Check the drawings carefully. Then see if you still have hum.
If the transformer is humming, I would first be concerned with your power. Noise or DC offset will cause the transformer to hum. Yes, you may have DC on your power lines.
You need to check your rectifiers. An open diode will cause lots of hum. Do you have any test equipment? 1N400x series diodes are dirt cheap, if you want to shotgun, you could do that.
If you don't understand exactly what Andrew said, I suggest you replace the main caps with modern high quality ones. You can probably go about twice as large and still not have problems with the lead spacing or height. Check the drawings carefully. Then see if you still have hum.
If the transformer is humming, I would first be concerned with your power. Noise or DC offset will cause the transformer to hum. Yes, you may have DC on your power lines.
You need to check your rectifiers. An open diode will cause lots of hum. Do you have any test equipment? 1N400x series diodes are dirt cheap, if you want to shotgun, you could do that.
Thanks guys , I think replacing like for like and setting the bias is the best I can do at the moment but I can follow instructions.
So the caps in the power amp will possibly need doing, those brown ones , what about the ones next to the heatsink? I suppose it wouldnt hurt to replace them as well.
What benefits do I gain from replacing the main caps with larger ones?
The hum is something that happened gradually , or at least I only noticed it a few months back. I have recently moved house but only down the road so it could still be dirty mains, no other appliances in the house hum , and I did unplug everything to see if it was being caused by the fridge or washing machine etc.
How do I go about checking the rectifiers?
So the caps in the power amp will possibly need doing, those brown ones , what about the ones next to the heatsink? I suppose it wouldnt hurt to replace them as well.
What benefits do I gain from replacing the main caps with larger ones?
The hum is something that happened gradually , or at least I only noticed it a few months back. I have recently moved house but only down the road so it could still be dirty mains, no other appliances in the house hum , and I did unplug everything to see if it was being caused by the fridge or washing machine etc.
How do I go about checking the rectifiers?
It is the big main caps you should be most concerned with. The two big ones with date codes on them. The ones that cost money. Be sure you get the same or slightly higher voltage rating. Not less, and be very sure you put then in correctly, plus vs minus. If not, they will blow up. Makes a really big mess.
Next are the 100u caps Jaycee mentioned above.
Do you have a multimeter? If you do, compare the AC on the plus to the AC on the minus rails. If the ripple is larger on one, you have a bad diode. If your meter has a "diode" range, then you can use it to test the diodes. Beep in one direction, no beep in the other. If you don't, hit e-bay for a cheap one that does. I use a idiot light.
If the hum came on slowly, then I would suspect caps as that is degrading vs failure. Like I said, rectifiers are cheap.
Larger caps are not magic. They will reduce the ripple a little, and provide a bit more reserve for repeated transients. It is one of those, "while you are there" things to do.
I have no idea if there are proper snubbers across your bridge, of an x-cap across the mains or transformer output. A cap failure there could also cause transformer hum.
Transformer hum bothers me. It should not be audible. Uneven load, DC, or loose winding.
Next are the 100u caps Jaycee mentioned above.
Do you have a multimeter? If you do, compare the AC on the plus to the AC on the minus rails. If the ripple is larger on one, you have a bad diode. If your meter has a "diode" range, then you can use it to test the diodes. Beep in one direction, no beep in the other. If you don't, hit e-bay for a cheap one that does. I use a idiot light.
If the hum came on slowly, then I would suspect caps as that is degrading vs failure. Like I said, rectifiers are cheap.
Larger caps are not magic. They will reduce the ripple a little, and provide a bit more reserve for repeated transients. It is one of those, "while you are there" things to do.
I have no idea if there are proper snubbers across your bridge, of an x-cap across the mains or transformer output. A cap failure there could also cause transformer hum.
Transformer hum bothers me. It should not be audible. Uneven load, DC, or loose winding.
Thanks TVRGeek, are these the rectifier diods?
An externally hosted image should be here but it was not working when we last tested it.
Hi robgilmo
In such old amplifiers can be assumed that all mechanical contacts are dirty or burned.
It makes a lot of work, but brings a lot. This is an action which one can also measure and actually listen
Replace the output relay(buy not a cheap one)and clean all mechanical contacts.
The two long switches you have to take apart to clean it. Make photos between , or you will not get it together anymore.
In such old amplifiers can be assumed that all mechanical contacts are dirty or burned.
It makes a lot of work, but brings a lot. This is an action which one can also measure and actually listen
Replace the output relay(buy not a cheap one)and clean all mechanical contacts.
The two long switches you have to take apart to clean it. Make photos between , or you will not get it together anymore.
Yes, those are the rectifier diodes. If your meter doesn't have a diode beeper, use the 2000 ohm scale. On my meter, silicon diodes (after 1962) read between 450 and 620 ohms forwards and 1999 backwards. Minus is the line forwards. You won't get a valid reading until one end of each diode is disconnected.
I would do one thing at a time and check your work by listening to the amp, not everything at once. Relay contacts can be a problem but hum is frequently an overage dry electrolytic capacitor problem.
I would do one thing at a time and check your work by listening to the amp, not everything at once. Relay contacts can be a problem but hum is frequently an overage dry electrolytic capacitor problem.
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In such old amplifiers can be assumed that all mechanical contacts are dirty or burned.
It makes a lot of work, but brings a lot. This is an action which one can also measure and actually listen
Replace the output relay(buy not a cheap one)and clean all mechanical contacts.
The two long switches you have to take apart to clean it. Make photos between , or you will not get it together anymore.
Thanks , anything else you can think of, trim pots perhaps?
As for the caps , there are 4 circuits, power amp (left and right) power supply, phono stage, muting and dc protection.
The caps in there are rubycon, would rubycon zl be Ok to replace all of them with?
What about resistors and transistors etc , would they be worn?
In theory I could replace the whole lot and have a brand new amp.
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Im going to do the caps and bias first. As you say one bit at a time and a listen inbetween.
Edit - A diode is a kind of a one way valve right? It wont allow current to pass back through itself?
Or have I got that entirely wrong?
Hello robgilmo,
From recapping the electorlytics in 5 amplifiers now, but all these amplifiers where made before 1990, and some from early 1970's. With amps of these sort of ages I suspect you will find that nearly any capacitor electrolytic capacitor you replace, may reduce the hum, some by a little some by a lot, and some/most will improve the sound quality, some by a little some by a lot, and in some amplifiers remove crackle on the tone/volume controls that people normally recomend contact cleaner for.
I usually up the voltage rating slightly, I go for branded low ESR or switching electrolytic capacitors. Currently I have been using Panasonic, and Nichicon and buying them from german companies (not ebay fakes). Usually I go one voltage rating higher, and ideally higher temperature tolerance. Every time I have done this with 1990's and older equipment I have found a significant improvement.
Your amplifiers red capacitors shown:
Look just like the ones that go first in Quad 303's from the 1970's.
The most important thing to do is make sure your new capacitors have the same or smaller diameter than the originals, and if possible the same lead spacing if PCB mounted. I usually only increase the capacitcance values (usually double) of the capacitors in the power supply
If capacitors are mounted using metal clips around the cicumfrance, I tend to use a punctured bike iner tube to wrap around the new capacitor to make up the diameter.
I have decided to replace some other types of capacitors, but always do the all the electrolytics is my advice. Replacing old film capatiors makes much less differance as these last.ceramic or other types of capacitors maybe replaces with modern film capacitors, and also look for opertunities to replace the smallest electrolytics (eg 2.2 uF) with film capacitors if its a very high end amp. Your speakers and amp will have to be good (and already recapped with new electrolytics) to justify the cost and notice the differance though.
Good luck
Owen
Do new non fake electrolytics (such as Panasonic or Nichicon) sound significantly different, and if they do which is a reasonable price / performance option?
From recapping the electorlytics in 5 amplifiers now, but all these amplifiers where made before 1990, and some from early 1970's. With amps of these sort of ages I suspect you will find that nearly any capacitor electrolytic capacitor you replace, may reduce the hum, some by a little some by a lot, and some/most will improve the sound quality, some by a little some by a lot, and in some amplifiers remove crackle on the tone/volume controls that people normally recomend contact cleaner for.
I usually up the voltage rating slightly, I go for branded low ESR or switching electrolytic capacitors. Currently I have been using Panasonic, and Nichicon and buying them from german companies (not ebay fakes). Usually I go one voltage rating higher, and ideally higher temperature tolerance. Every time I have done this with 1990's and older equipment I have found a significant improvement.
Your amplifiers red capacitors shown:
An externally hosted image should be here but it was not working when we last tested it.
Look just like the ones that go first in Quad 303's from the 1970's.
The most important thing to do is make sure your new capacitors have the same or smaller diameter than the originals, and if possible the same lead spacing if PCB mounted. I usually only increase the capacitcance values (usually double) of the capacitors in the power supply
If capacitors are mounted using metal clips around the cicumfrance, I tend to use a punctured bike iner tube to wrap around the new capacitor to make up the diameter.
I have decided to replace some other types of capacitors, but always do the all the electrolytics is my advice. Replacing old film capatiors makes much less differance as these last.ceramic or other types of capacitors maybe replaces with modern film capacitors, and also look for opertunities to replace the smallest electrolytics (eg 2.2 uF) with film capacitors if its a very high end amp. Your speakers and amp will have to be good (and already recapped with new electrolytics) to justify the cost and notice the differance though.
Good luck
Owen
Do new non fake electrolytics (such as Panasonic or Nichicon) sound significantly different, and if they do which is a reasonable price / performance option?
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Measurement removes a lot of guesswork! Everybody doing this sort of thing should buy or build some kind of cap bridge or ESR meter. That said, low voltage caps like 6.3 and 10V can have a remarkably short life and high failure rate. I always replace them with 16V minimum. Those red ones would be prime candidates. As for the rest, IMO it's a really bad idea to just replace things without understanding what's wrong and fixing it first. Once you (or somebody) fixes the hum, and there will be some specific reason for it, then worry about recapping the whole thing. You shouldn't mess with the diodes if they check OK on a meter with a diode check function.
replacing caps
conrad, I purchased new 15 years ago a Quanity of Mallory made in USA 7500MFD 60V DC. I reformed one of them slowly using my bench supply and a resistor. I check the value with my cap. meter and used my Jackson VTVM on the R * 100 scale and watch how slowly it discharces. Are you saying it is best to buy a new cap or or esr check it. Also I have collected over the years many polyester foil and film caps. by famous brands which always had a band or line on one lead side. When you buy an equivalent it is more than half the size. what is your opinion about vibality fo the NOS caps. Yero
conrad, I purchased new 15 years ago a Quanity of Mallory made in USA 7500MFD 60V DC. I reformed one of them slowly using my bench supply and a resistor. I check the value with my cap. meter and used my Jackson VTVM on the R * 100 scale and watch how slowly it discharces. Are you saying it is best to buy a new cap or or esr check it. Also I have collected over the years many polyester foil and film caps. by famous brands which always had a band or line on one lead side. When you buy an equivalent it is more than half the size. what is your opinion about vibality fo the NOS caps. Yero
Hi Yero,
My take is that people are way to anxious to replace caps without first measuring to see if there's anything wrong with them. Caps that have low losses and correct values are very unlikely to fail anytime soon. When caps go bad they usually do so slowly. Naturally there's an exception to every rule! No one can guarantee your amp won't go up in smoke tomorrow, and that's even if you install brand new parts today.
I have a huge number of NOS caps and have seen little to no degradation, maybe with the exception of low voltage electrolytics like 6.3 and 10V caps. Or maybe they were just crummy to begin with. I also don't completely trust HV caps, say 200V and up without careful reforming and evaluation.
Films you don't have to worry about at all. As for size, smaller isn't always better.
Would I recap something with NOS parts? Probably not, unless the caps were showing real signs that they were reaching their end of life and I didn't think investing in new was worth it. Would I repair something that had failed with NOS parts? Absolutely. Would I build DIY with NOS parts? Do it all the time. (When I do work for somebody else, I do pretty much whatever they want, unless it's just too foolish or unsafe.)
FWIW, I just picked up a Sansui 2000x receiver at the dump. Covered in mud. It was built when I was in high school, around 1972, 40 years ago. I cleaned it up and checked most every cap in it. Every cap was within tolerance and showed low losses, lower than many new ones. Only a neurotic would recap something like that. I'm not against replacing caps that need replacing, nor against replacing caps where similar caps have gone bad, but replacing caps that exceed their specs, especially for losses, makes no sense. (The Sansui mostly needed dial lights.)
My take is that people are way to anxious to replace caps without first measuring to see if there's anything wrong with them. Caps that have low losses and correct values are very unlikely to fail anytime soon. When caps go bad they usually do so slowly. Naturally there's an exception to every rule! No one can guarantee your amp won't go up in smoke tomorrow, and that's even if you install brand new parts today.
I have a huge number of NOS caps and have seen little to no degradation, maybe with the exception of low voltage electrolytics like 6.3 and 10V caps. Or maybe they were just crummy to begin with. I also don't completely trust HV caps, say 200V and up without careful reforming and evaluation.
Films you don't have to worry about at all. As for size, smaller isn't always better.
Would I recap something with NOS parts? Probably not, unless the caps were showing real signs that they were reaching their end of life and I didn't think investing in new was worth it. Would I repair something that had failed with NOS parts? Absolutely. Would I build DIY with NOS parts? Do it all the time. (When I do work for somebody else, I do pretty much whatever they want, unless it's just too foolish or unsafe.)
FWIW, I just picked up a Sansui 2000x receiver at the dump. Covered in mud. It was built when I was in high school, around 1972, 40 years ago. I cleaned it up and checked most every cap in it. Every cap was within tolerance and showed low losses, lower than many new ones. Only a neurotic would recap something like that. I'm not against replacing caps that need replacing, nor against replacing caps where similar caps have gone bad, but replacing caps that exceed their specs, especially for losses, makes no sense. (The Sansui mostly needed dial lights.)
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Here's what I'd do:
Change the 2 main PSU capacitors
Change the 4 capacitors near the heatsink
Change the two 100uF 10V Roederstein capacitors
If you use the phono stage, change all of the capacitors there
Replace the volume pot
I don't believe in brand hype - theres nothing wrong with Rubycon ZL, but dont go out of your way to get them. Panasonic FC series are just as good and easily available. If you compile a parts list of capacitors already in the unit, I can suggest what to pick.
Trimmers, resistors etc - leave those alone. Those generally only fail if there's a fault. The Iskra trimmers used in this amp are good quality and will still be fine.
There's only one tweak Id be tempted to make IF you use the phono stage, and that is replace the opamp. If it's an LM833 as I think it is, replace it with an NE5532. They're cheap, and a whole lot better. Others may suggest fancy modern opamps but I don't feel it's worth it for just a straight swap.
Oh, you should be fine losing your balance control - not wiring one in should produce the same effect as the control being centered.
Change the 2 main PSU capacitors
Change the 4 capacitors near the heatsink
Change the two 100uF 10V Roederstein capacitors
If you use the phono stage, change all of the capacitors there
Replace the volume pot
I don't believe in brand hype - theres nothing wrong with Rubycon ZL, but dont go out of your way to get them. Panasonic FC series are just as good and easily available. If you compile a parts list of capacitors already in the unit, I can suggest what to pick.
Trimmers, resistors etc - leave those alone. Those generally only fail if there's a fault. The Iskra trimmers used in this amp are good quality and will still be fine.
There's only one tweak Id be tempted to make IF you use the phono stage, and that is replace the opamp. If it's an LM833 as I think it is, replace it with an NE5532. They're cheap, and a whole lot better. Others may suggest fancy modern opamps but I don't feel it's worth it for just a straight swap.
Oh, you should be fine losing your balance control - not wiring one in should produce the same effect as the control being centered.
Conrad & I have tangled before. Measuring a cap proves it has enough water today. It does not prove the integrity of the cap seal, which in a consumer product is probably rubber. Conrad is the kind of guy who would measure the air pressure in his 1970 tires on his 1970 car before taking it out on the freeway. If you are going to measure a cap in a twenty year old product, you should remove it and test it once a month. Organ forum is full of people that bought a great sounding old organ that hasn't been played in 15 years, that went to **** in two weeks of real use. I'm with Enzo , that totally re-e-caps most of the products that enter his shop. Perhaps Conrad has only owned high end products that contain only epoxy sealed caps. Such products are not even for sale in my metropolitan area. The newer the product, the shorter life the caps in it are, it seems. My DTV converter had bad caps the day I brought it home from W***-M***. My 6 year old computer mainboard quit talking last week- 2 e-caps were bulging. I've recently received the order to replace all the rest of them, and avoid buying a new *****y import computer product with a 2 year design life. The caps themselves are not expensive. I'm paying an average of $.25 for 100 to 3300 low voltage caps. Even the 10000 uf 100V caps in my Peavey amp, I was able to get the cost down to $10 each by buying 4700 uf caps and jumpering the PC board to new holes I drilled.
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Indianajo, I not surprised at what you think since I recently repaired an organ amp. Between the original POS design and the repairs subsequently made by others over the years, I would have liked to replace not only the caps, but the entire amp and much of what was connected to it!
In a tube amp you have voltage and heat issues that will cause rapid failure of caps, and the worst case seems to be if the amp isn't kept in active service. The organ amp also relied on field coil speakers to keep the supply loaded down sufficiently so as not to blow the PS caps. Even with that they were over stressed and relied entirely on their surge rating during power up.
IMO, that sort of design (and I use the term loosely) has absolutely nothing to do with the sorts of low voltage circuitry typically discussed here. The cap failure modes will be different. As for rubber, you don't seem to have a high regard for the stuff. In hot HV tube amps I can see why.
In LV circuitry with low stresses on the caps (most solid state audio stuff) 40+ year life for caps is common, in fact it's probably typical if the original parts weren't junk, and I'm not talking about epoxy seals. I have somewhere between 5 and 10K pieces of NOS capacitors around here, so my data pool on aging isn't insignificant. Some of my tube test equipment goes back to the '40s and is still going strong with no recaps- I power it up and use it regularly to avoid degradation.
I do agree that many modern caps aren't very good, so that should be a caution to those rushing into a recap!
IMO, for the stuff you work on, replacing caps makes perfect sense. That doesn't mean it's the right choice for everybody in every situation.
In a tube amp you have voltage and heat issues that will cause rapid failure of caps, and the worst case seems to be if the amp isn't kept in active service. The organ amp also relied on field coil speakers to keep the supply loaded down sufficiently so as not to blow the PS caps. Even with that they were over stressed and relied entirely on their surge rating during power up.
IMO, that sort of design (and I use the term loosely) has absolutely nothing to do with the sorts of low voltage circuitry typically discussed here. The cap failure modes will be different. As for rubber, you don't seem to have a high regard for the stuff. In hot HV tube amps I can see why.
In LV circuitry with low stresses on the caps (most solid state audio stuff) 40+ year life for caps is common, in fact it's probably typical if the original parts weren't junk, and I'm not talking about epoxy seals. I have somewhere between 5 and 10K pieces of NOS capacitors around here, so my data pool on aging isn't insignificant. Some of my tube test equipment goes back to the '40s and is still going strong with no recaps- I power it up and use it regularly to avoid degradation.
I do agree that many modern caps aren't very good, so that should be a caution to those rushing into a recap!
IMO, for the stuff you work on, replacing caps makes perfect sense. That doesn't mean it's the right choice for everybody in every situation.
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