I'm working on the family Philco 51-1732 and I would like to replace the electrolytic capacitors, but it's mutliple capacitors in one can and I haven't been able to find the correct replacements. The needed values according to the manual are 2 40uf, one rated at 350V and one 400v, and a 60uf at 400v. I can find 33uf, 47uf, and 100. I could potential get my hands on a 80uf 450v. I've attached the section of the schematic with the capacitors in case it would make more sense to do something different. I have the full schematic as well if necessary. As a hobby I do a fair amount of work with electronics but mostly just parts swapping, so thanks for any help!
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Higher voltages are ok too so look for caps with 450 volt rating as they are easier to find. The first 40uf section must be that value but the other sections can be a little larger. You can always use individual caps placed under the chassis and leave the disconnected multi section cap in place for looks. A 33uf cap could be used instead of the 40uf with little change or you can parallel two caps to get 40uf.
Thanks for the reply! So I have to have 40uf one way or the other on the first one, but the other two I could use a 33uf and 80uf?
No, the first capacitor can just be 33uF, no biggie.
You won't find a 40uF part these days.
Others as you mentioned. They can all be 350 or 400 VDC.
You won't find a 40uF part these days.
Others as you mentioned. They can all be 350 or 400 VDC.
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You don’t have to use a 40uf on the first one but don’t go any larger on it. The rectifier tube will not last if you increase that cap. The others should be the schematic value or slightly larger is ok on them. A 33uf first cap is ok but 40uf is better at getting the right voltage and lowering hum. To get to 40ut you can parallel caps that add up to 40uf.
I've got my caps in and I'm studying the schematic to figure out the best way to wire things in. I bought an 18 and 22 UF cap to get the 40uf I need. mdpaudio can you tell me which one you meant as the "first section"? The one closest to the rectifier, C47D in the diagram?
That’s a perfect way to get to the 40uf. You know to parallel them, positive together and minus together. Yes, by first section I mean the first cap after the rectifier tube. Every type of tube rectifier has a different maximum value for the first cap, go bigger and you’ll fry the tube. Later sections can be a little larger than originally used. They were not made bigger at the time of build because electrolytic caps were very expensive and not easy to make large back then. Now they are cheap and easy to get, sounds like me after a few drinks! You can snip the terminals off the can cap to leave it in place for looks and just wire the new caps to the points where they originally went. Make sure you insulate the leads well as there is very high voltage on them. If you want to gild the lily you can put very small film caps in parallel with the electrolytics. Some say it does nothing and others like me think it helps deliver current to the circuit faster giving a cleaner sound. It’s up to you. Measure the resistors used between the cap sections before they are reconnected as they frequently drift off value due to the long term heat exposure. Good luck and enjoy the process!
I'm going to have to move the capacitors to a different location in the case due to their size. For the first section I got two Solen Fast caps and they are pretty big. I'm guessing due to their design I probably don't need to do the film caps for those? What film cap rating would you suggest for that purpose though? I also found the C47A in the schematic which is for the 6y6g output tube, so I'm going to replace that as well. I tested the resistors and they both were in spec, but I wonder if I should change them anyway being over 70 years old. One is a 2w 2500ohm resistor, and the closest I've found is a 2400ohm 2w. Should I add a 100ohm resistor to nail 2500 or is it that critical? The other is a 7w 330ohm, and I can find that one no problem. And, final question, hopefully, what wire would be appropriate for hooking up the caps, 20ga solid strand? Thank you for all the help!
20 gauge is ok but 18 is better for power supply. I use solid core Teflon jacket from ApexJr on eBay .solid wire dresses better so you can put it where you want and it doesn’t move. You’re using film caps already so you don’t need to bypass it. If you were using electrolytics you would bypass with film caps of 630v and anything from .1uf to 10% of the value of the electrolytic. I use all film caps as well. ApexJr has so cheap 75uf 600v film caps for $5 each which is a good price and they are well made.
2400 is close enough to the value in a power supply. It would be too far off for a signal path use. For the 7w use a 12 watt Mills resistor. They are expensive but you can’t go wrong with quality. You could even use a Mills for the 2500ish resistor. Mills are smaller than other brands and well made.
2400 is close enough to the value in a power supply. It would be too far off for a signal path use. For the 7w use a 12 watt Mills resistor. They are expensive but you can’t go wrong with quality. You could even use a Mills for the 2500ish resistor. Mills are smaller than other brands and well made.
You really don’t need fancy expensive caps for this. Electrolytics would be fine, and much smaller so they could fit under the chassis.
Linear power supplies can vary quite widely in their output voltages. A change of a couple volts from the mains can swing 10s of volts in the HT. So getting precise values isn’t critical. Your tube won’t notice 2.4k vs 2.5k ohms. The tolerance band would probably cover that anyway. (Remember that it’s 2.5k ohms +/- 10 or even 20%. Same with the caps.)
Linear power supplies can vary quite widely in their output voltages. A change of a couple volts from the mains can swing 10s of volts in the HT. So getting precise values isn’t critical. Your tube won’t notice 2.4k vs 2.5k ohms. The tolerance band would probably cover that anyway. (Remember that it’s 2.5k ohms +/- 10 or even 20%. Same with the caps.)
I’m a little partial to 600v or better on my film caps just because things can happen to go overvoltage at startup. It’s harder to find electrolytic caps over 450v you can but they are expensive. Film caps are much larger but usually can be stuffed somewhere under the chassis.
I finally found C47A in the schematic, which was the remaining electrolytic cap. Got all my components together and soldering in the 18uf and 22uf Solen Fast caps for C47D and a 10uf Fast cap for C47A, for C47B I put in the 47uf electrolytic along with a .22uf film cap, while C47C got a 80uf electrolytic with a .22uf film cap as well. Where reasonable I replaced the existing 20 gauge solid strand with 18, and I was able to fit everything inside the existing chassis. When I got everything together I was disappointed to still have a very pronounced 60 cycle hum as the tubes warmed that came in about half volume but only on the phono. I ended up swapping the 7F8 converter tube that I had purchased for the original that I had removed from the amp and not only get a slight hum at say 80% volume or higher. I'm assuming the 7F8 I bought is defective, but I'm unsure. Also, is there anyway to clean up that last bit of hum or is it best to leave it be? Made great progress so far, and figured I would post all this in case some one else wanted to resurrect this unit. Thanks everyone!