I am restoring a old 1929 radio the schematic shows three 1mfd and one 1.5mfd across the secondary of the transformer, was there such a thing as electrolytics that size in the early days? even though the schematic does not say they are electrolytics or show + or - I am assuming that is what they are, the originals are the old box type and no writing on them or wore off,the schematic is under model 41 of us radio & television in this site in case you want to look for yourself,someone at some time installed a 8mfd/600 box type , but left the others still conected am I safe to replace each with a more modern say 4.7/450 volt for each? also it calls for 1mfd for a few paper caps aren't these the same as a modern .001?
Thanks for your help
Elton

Hi Elton

Older radios with those values would have used paper type caps. Electrolytics weren't as available at that time.

If the radio has an 80 rectifier you can use 4.7 mf @ 450 volt electrolytic caps. Unlikely but if your radio uses 81 rectifiers higher voltage rating may be needed. Disconnect old caps.

The most positive voltage in a radio is filament of the rectifier. Most negative, center tap of transformer high voltage winding. This should help with polarity?

1 mfd is the same as modern caps of this value, not .001. These are available.

One other thing. Caps should not be across the transformer but rather after your rectifier tube.

Norm

:I am restoring a old 1929 radio the schematic shows three 1mfd and one 1.5mfd across the secondary of the transformer, was there such a thing as electrolytics that size in the early days? even though the schematic does not say they are electrolytics or show + or - I am assuming that is what they are, the originals are the old box type and no writing on them or wore off,the schematic is under model 41 of us radio & television in this site in case you want to look for yourself,someone at some time installed a 8mfd/600 box type , but left the others still conected am I safe to replace each with a more modern say 4.7/450 volt for each? also it calls for 1mfd for a few paper caps aren't these the same as a modern .001?
:Thanks for your help
:Elton
:

This was probably not an electolytic capacitor.

When you say the box type capacitor, I think I know what you are talking about, so let me make my guess, and correct me if I am wrong - I'm guessing the cap you are describing is plastic, rectangle, and colored dots on it.

You should be able to easily find a modern replacment. Look for either ceramic disc or you may be able to find an electrolytic, just make sure it is NON-POLORIZED.

No these are cardboard box type which led me to beleive these were paper caps this is where the confusion started, all of them are shot and show signs of leakage, Thanks to you and norm for setting me straight. but I have another question , when did electrolytics first start to be used commonly in radios?
Thanks again.
:This was probably not an electolytic capacitor.
:
:When you say the box type capacitor, I think I know what you are talking about, so let me make my guess, and correct me if I am wrong - I'm guessing the cap you are describing is plastic, rectangle, and colored dots on it.
:
:You should be able to easily find a modern replacment. Look for either ceramic disc or you may be able to find an electrolytic, just make sure it is NON-POLORIZED.

Electrolytic condensers were commercially introduced by AMRAD (as the Mershon condenser) in about 1926. They were first extensively used by Crosley in their 1928 light socket sets. Until around 1930 most other manufacturers used paper condensers of either 1 or 2 microdards in a 5 step condenser input filter (condenser-choke-condenser-choke-condenser), usually with another 1mfd condenser connected across the detector section of the voltage divider. Most of the early paper filter condensers were potted into rectangular tin boxes. The condensers in cardboard boxes that you noticed are probably mid 1930's vintage dry electrolytics.

: No these are cardboard box type which led me to beleive these were paper caps this is where the confusion started, all of them are shot and show signs of leakage, Thanks to you and norm for setting me straight. but I have another question , when did electrolytics first start to be used commonly in radios?
:Thanks again.
::This was probably not an electolytic capacitor.
::
::When you say the box type capacitor, I think I know what you are talking about, so let me make my guess, and correct me if I am wrong - I'm guessing the cap you are describing is plastic, rectangle, and colored dots on it.
::
::You should be able to easily find a modern replacment. Look for either ceramic disc or you may be able to find an electrolytic, just make sure it is NON-POLORIZED.

Bob, you are correct in the way these are used in this case a cap then a choke then another cap etc,but the cardboard boxes are so old there is no markings on them at all so I do not know if these were a electrolytic or a paper cap.So I guess the millon dollar question is, should I just replace the old with a more modern paper cap of the right specs? or should I use modern polerized electrolytics to replace the caps that were originally paper to begin with, after the rectifer? would this effect the radio in anyway?
thanks for your help.
:Electrolytic condensers were commercially introduced by AMRAD (as the Mershon condenser) in about 1926. They were first extensively used by Crosley in their 1928 light socket sets. Until around 1930 most other manufacturers used paper condensers of either 1 or 2 microdards in a 5 step condenser input filter (condenser-choke-condenser-choke-condenser), usually with another 1mfd condenser connected across the detector section of the voltage divider. Most of the early paper filter condensers were potted into rectangular tin boxes. The condensers in cardboard boxes that you noticed are probably mid 1930's vintage dry electrolytics.
:
:
:: No these are cardboard box type which led me to beleive these were paper caps this is where the confusion started, all of them are shot and show signs of leakage, Thanks to you and norm for setting me straight. but I have another question , when did electrolytics first start to be used commonly in radios?
::Thanks again.
:::This was probably not an electolytic capacitor.
:::
:::When you say the box type capacitor, I think I know what you are talking about, so let me make my guess, and correct me if I am wrong - I'm guessing the cap you are describing is plastic, rectangle, and colored dots on it.
:::
:::You should be able to easily find a modern replacment. Look for either ceramic disc or you may be able to find an electrolytic, just make sure it is NON-POLORIZED.

What Norm said is good. You may use electrolytics in place of most of the paper filter caps. There are places where this is unnecessary. Anywhere far down the filter line where values less than .9 MFD are used may be replaced with same type non-polarized condensers (for instance .5 or .1 MFD). For the paper condensers closer to the rectifier, you may replace them with electrolytics from 4 to 20 MFD. Higher capacitance may or may not improve hum conditions. It will most likely improve matters. Some filter systems were specially tuned so that they could make use of the small condenser sizes, and may or may not work with larger values. Do not go over 30 MFD on the lead condenser, as the rectifier must be able to charge this at turn-on. Higher values can overload the rectifier and cause a flash. Honestly, though, values no higher than 20 MFD will do fine. You could replace all large value paper condensers with 20 MFD electrolytics, or you could taper them down as you moved away from the rectifier, as was commonly done. In this case, go with a 20 or 16 at the beginning, and then go for a 16 or 10, and after that go with 10 or 8 for all others.

Also, having higher electrolytic values other than the original low values may improve bass response, giving you more bass volume at higher audio volumes. With the original small value condensers it was easier to load down the power supply and drain them with heavy bass notes. The larger value condensers will hold their charge longer.

Thomas

Thanks to all of you for your inputs, I rec'd this radio and the former owner said when he turned it on all he got was a bad motorboat out of it, I just wanted to be sure of what I could use not being sure with the schematic as vague as it was , I did not want to blow it up with the wrong componets.
Thanks
Elton
:What Norm said is good. You may use electrolytics in place of most of the paper filter caps. There are places where this is unnecessary. Anywhere far down the filter line where values less than .9 MFD are used may be replaced with same type non-polarized condensers (for instance .5 or .1 MFD). For the paper condensers closer to the rectifier, you may replace them with electrolytics from 4 to 20 MFD. Higher capacitance may or may not improve hum conditions. It will most likely improve matters. Some filter systems were specially tuned so that they could make use of the small condenser sizes, and may or may not work with larger values. Do not go over 30 MFD on the lead condenser, as the rectifier must be able to charge this at turn-on. Higher values can overload the rectifier and cause a flash. Honestly, though, values no higher than 20 MFD will do fine. You could replace all large value paper condensers with 20 MFD electrolytics, or you could taper them down as you moved away from the rectifier, as was commonly done. In this case, go with a 20 or 16 at the beginning, and then go for a 16 or 10, and after that go with 10 or 8 for all others.
:
:Also, having higher electrolytic values other than the original low values may improve bass response, giving you more bass volume at higher audio volumes. With the original small value condensers it was easier to load down the power supply and drain them with heavy bass notes. The larger value condensers will hold their charge longer.
:
:Thomas

Moterboating can be caused by many things (missing shields, speaker leads too close to amplifier tubes, etc.), but is often caused by faulty filter condensers. Filter condensers are what stabilize the supply current for the tubes (B current). If nothing stabilizes the current properly, fluctuations happening in one circuit (amplified radio or audio signals) will pass on to another circuit where they don't belong, and will cause feedback. Of course if the filters are bad, you will also likely hear 60 cycle AC hum. With the older AC radios, however, they used so many chokes and hum bucking coils that hum may be less noticeable. They did this because of the lack of availability of large filter condensers.

Thomas

Thomas, I would venture to guess it is the caps, all of them except the box filters are ozing their guts out
so I will take your and Norm's advise and use electrolytics in place of the old box 1 mfd's and replace all the other by-pass caps with new and then slowly bring it up on my variac and see what happens.
Thanks agian
Elton
:Moterboating can be caused by many things (missing shields, speaker leads too close to amplifier tubes, etc.), but is often caused by faulty filter condensers. Filter condensers are what stabilize the supply current for the tubes (B current). If nothing stabilizes the current properly, fluctuations happening in one circuit (amplified radio or audio signals) will pass on to another circuit where they don't belong, and will cause feedback. Of course if the filters are bad, you will also likely hear 60 cycle AC hum. With the older AC radios, however, they used so many chokes and hum bucking coils that hum may be less noticeable. They did this because of the lack of availability of large filter condensers.
:
:Thomas