Hi all!
I was working on an Olymic, model 550-551 and want to replace the filter capacitor, a 70 mfd @150V and a 30 mfd @ 150V. I have two 47 mfd capacitors @ 160V. Can I use a 47 mfd in place of the 70 mfd?
I thank you for any and all input you may have.
Thank you all!!
Yours Truely,
Daniel

I did not see the schematic for this radio here, but you may be able to use 47 MFD capacitors to replace both units. This sounds like an AC/DC radio, which, with the typical filter arrangement, uses a 50/30 combination. A few used more, and some used less, such as 20/20 or 30/30.

You can always go lower with capacitance. Try it and see if hum is agreeable. Going higher can be dangerous because you can overload the rectifier at warm turn-on, so never go higher than the original specified value unless data in a tube manual says that the rectifier tube in question can handle more input capacitance with a filter circuit that is similar to what is described in the tube manual.

T.

:I did not see the schematic for this radio here, but you may be able to use 47 MFD capacitors to replace both units. This sounds like an AC/DC radio, which, with the typical filter arrangement, uses a 50/30 combination. A few used more, and some used less, such as 20/20 or 30/30.
:
:You can always go lower with capacitance. Try it and see if hum is agreeable. Going higher can be dangerous because you can overload the rectifier at warm turn-on, so never go higher than the original specified value unless data in a tube manual says that the rectifier tube in question can handle more input capacitance with a filter circuit that is similar to what is described in the tube manual.
:
:T.
:
Dear Mr. Dermody, I am very greatful for your input, I never knew that going higher in capactance could be a problem. I am learning here. Thank you sir kindly for the help. I need to rethink some other radio projects as well!! Thank you again!!!!
Daniel

It could be but isn't necessarily a problem.

In general it's a good idea to stay close to original values regarding capacitance. For RF circuits a change in capacitance will affect frequency and frequency response (often critical). In audio circuits a change will affect frequency response (not critical, but a large increase may saturate the amplifier with more bass than it was designed to handle, causing distortion at lower volumes that what might otherwise be achieved). A change in capacitance in the power filter circuit of a radio will, of course, affect filtering. Generally an increase in parallel capacitance will decrease hum (to a fair limit), and a decrease in parallel capacitance will increase hum. Excessive input capacitance can burn out rectifiers (see specifications of rectifier in question, if available). Some of the earliest AC radios contain tuned filters, in which capacitance is rather critical, and values should be held close to original specifications.

T.

:It could be but isn't necessarily a problem.
:
:In general it's a good idea to stay close to original values regarding capacitance. For RF circuits a change in capacitance will affect frequency and frequency response (often critical). In audio circuits a change will affect frequency response (not critical, but a large increase may saturate the amplifier with more bass than it was designed to handle, causing distortion at lower volumes that what might otherwise be achieved). A change in capacitance in the power filter circuit of a radio will, of course, affect filtering. Generally an increase in parallel capacitance will decrease hum (to a fair limit), and a decrease in parallel capacitance will increase hum. Excessive input capacitance can burn out rectifiers (see specifications of rectifier in question, if available). Some of the earliest AC radios contain tuned filters, in which capacitance is rather critical, and values should be held close to original specifications.
:
:T.
:
Thank you again for the great input, Mr Dermody!! The prople that reply to these question are of great talent in electronics and I am so greatful for you and all the other great people on this forum the is willing to share their knowledge!! All have a great day!!
Daniel

::It could be but isn't necessarily a problem.
::
::In general it's a good idea to stay close to original values regarding capacitance. For RF circuits a change in capacitance will affect frequency and frequency response (often critical). In audio circuits a change will affect frequency response (not critical, but a large increase may saturate the amplifier with more bass than it was designed to handle, causing distortion at lower volumes that what might otherwise be achieved). A change in capacitance in the power filter circuit of a radio will, of course, affect filtering. Generally an increase in parallel capacitance will decrease hum (to a fair limit), and a decrease in parallel capacitance will increase hum. Excessive input capacitance can burn out rectifiers (see specifications of rectifier in question, if available). Some of the earliest AC radios contain tuned filters, in which capacitance is rather critical, and values should be held close to original specifications.
::
::T.
::
:Thank you again for the great input, Mr Dermody!! The prople that reply to these question are of great talent in electronics and I am so greatful for you and all the other great people on this forum the is willing to share their knowledge!! All have a great day!!
:Daniel
:
If you have a larger cap than specified you can use it if you either check tube ratings or insert a thermister in tube current path. Larger capacitors in filters almost always improve performance because the designers were limited on cap size by cost objectives. But, except for large inrush currents, the few times a larger cap gets you in trouble you can hear the poor performance and change out the large cap.

:::It could be but isn't necessarily a problem.
:::
:::In general it's a good idea to stay close to original values regarding capacitance. For RF circuits a change in capacitance will affect frequency and frequency response (often critical). In audio circuits a change will affect frequency response (not critical, but a large increase may saturate the amplifier with more bass than it was designed to handle, causing distortion at lower volumes that what might otherwise be achieved). A change in capacitance in the power filter circuit of a radio will, of course, affect filtering. Generally an increase in parallel capacitance will decrease hum (to a fair limit), and a decrease in parallel capacitance will increase hum. Excessive input capacitance can burn out rectifiers (see specifications of rectifier in question, if available). Some of the earliest AC radios contain tuned filters, in which capacitance is rather critical, and values should be held close to original specifications.
:::
:::T.
:::
::Thank you again for the great input, Mr Dermody!! The prople that reply to these question are of great talent in electronics and I am so greatful for you and all the other great people on this forum the is willing to share their knowledge!! All have a great day!!
::Daniel
::
:If you have a larger cap than specified you can use it if you either check tube ratings or insert a thermister in tube current path. Larger capacitors in filters almost always improve performance because the designers were limited on cap size by cost objectives. But, except for large inrush currents, the few times a larger cap gets you in trouble you can hear the poor performance and change out the large cap.
:
Mr. Mancini, Thank you Sir, for your input, with the replies on this subject I have become very educated on the use of capacitors and I am so very greatful for your help!!!!! Thank you again!!!
Daniel

Daniel:
You can sometimes easily use larger filter caps in a power supply filter circuit as long as it is not the first cap right after the rectifier.

Before it charges up ...that first cap can look like a momentary dead short to the rectifier tube when the power is first turned on.

The rectifier tubes are each individually rated to handle only a specific amount of in-rush current as well as a max operating current. In the tube manual the max input filter cap size is usually listed.

If the first cap in your power supply circuit is already of a value specified in the tube manual as the max suggested value, then it would not be advisable to try to increase it.

However in a typical "pi" filter there is a resistor after the first filter cap followed by a second filter cap. While it is always advisable to follow the original values in a circuit as shown on the schematic, if you need to or desire to reduce hum ....or if you simply do not have the exact value on hand at repair time, ...you can easily increase the value of that second filter cap quite significantly without damage to the rectifier. For instance if the second cap is shown on the schematic as a 30uf value you can easily use a 47uf or even somewhat higher value like 60uf or so and not cause a problem to the rectifier.

:Daniel:
:You can sometimes easily use larger filter caps in a power supply filter circuit as long as it is not the first cap right after the rectifier.
:
:Before it charges up ...that first cap can look like a momentary dead short to the rectifier tube when the power is first turned on.
:
:The rectifier tubes are each individually rated to handle only a specific amount of in-rush current as well as a max operating current. In the tube manual the max input filter cap size is usually listed.
:
:If the first cap in your power supply circuit is already of a value specified in the tube manual as the max suggested value, then it would not be advisable to try to increase it.
:
:However in a typical "pi" filter there is a resistor after the first filter cap followed by a second filter cap. While it is always advisable to follow the original values in a circuit as shown on the schematic, if you need to or desire to reduce hum ....or if you simply do not have the exact value on hand at repair time, ...you can easily increase the value of that second filter cap quite significantly without damage to the rectifier. For instance if the second cap is shown on the schematic as a 30uf value you can easily use a 47uf or even somewhat higher value like 60uf or so and not cause a problem to the rectifier.
:
Dear Mr. Balazsy,
I thank you as well for the information you supplied here. This must have been a good question to ask and from the replies I have learned a ton of information when recapping a vintage radio. I am so very greatful to everyone that replied to this question. Have a great day!!!
Daniel