For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
Doug
:Hey gang it's been awhile! I have a philco 77 with a huge condenser ("filter brick" as I call it.) section.
:with 3 x 2mf sections and one .15mf section. This radio still works as is, and these bricks seem to be pretty tough as compared to the can type used later. However since this set is over 80, I probably should roll up the sleeves and get in there and re-do the whole thing to save a smoky day! My question: Later radios have higher mfs ie 8, 10 ,12 ect. in these sections, should I ad more filtering? what would be a good recomendation? (I do see the 77a model pumps up one sectiom to 3mf and another from .15 to.45.)
I would agree with Doug's last statement, leave the cap out between #4 and #5 in the schematic. It's there to make a tuned circuit with the choke to reduce hum. This cap isn't needed when other filter cap values are increased. If not a fairly exact value this cap will actually increase hum.
Norm
:Here is the schematic: http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
:
:For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
:
:The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
:
:I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
:Doug
:
::Hey gang it's been awhile! I have a philco 77 with a huge condenser ("filter brick" as I call it.) section.
::with 3 x 2mf sections and one .15mf section. This radio still works as is, and these bricks seem to be pretty tough as compared to the can type used later. However since this set is over 80, I probably should roll up the sleeves and get in there and re-do the whole thing to save a smoky day! My question: Later radios have higher mfs ie 8, 10 ,12 ect. in these sections, should I ad more filtering? what would be a good recomendation? (I do see the 77a model pumps up one sectiom to 3mf and another from .15 to.45.)
Knowing that, personally I would experiment with a variety of film cap values, say starting at 0.05 uF and working up from there - seeing if I could find the one that best reduced the hum. (Even by jacking up the filter cap values, I presume there might be some residual hum?)
It seems from looking at the differences between the Models 77 and 77A, Philco must have been battling hum complaints. The 77A has a larger cap across the power choke (0.45 vs. 0.15 uF). That implies to me that they also jacked up the inductance of the choke on the Model 77A? Do my proposed experiment, and report the results.
Filter caps on early sets were often a bit skimpy. Before the advent of inexpensive, compact e-caps, radio manufacturers often used bulky, expensive, high-value paper caps. Ergo, the filter choke and its shunt cap for blocking the 60 Hz.
I always hate going too far in jacking up the value of filter caps - because of the wear and tear they impose on rectifier tubes at start up. But maybe with the early 1930s sets, with skimpy filter caps, this is less of a concern?
Doug
:Hi
:
: I would agree with Doug's last statement, leave the cap out between #4 and #5 in the schematic. It's there to make a tuned circuit with the choke to reduce hum. This cap isn't needed when other filter cap values are increased. If not a fairly exact value this cap will actually increase hum.
:
:Norm
:
:
:
::Here is the schematic: http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
::
::For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
::
::The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
::
::I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
::Doug
Although I didn't see it written would expect 77A was made for 25 cycle operation. A lower frequency would require a larger cap value.
Since this radio uses a full wave rectifier frequency of the tuned circuit would be 120 cycles and 50 cycles if the A version was made for 25 cycles operation.
Norm
:Thanks, Norm, for explaining the purpose of that cap shunting the choke. The idea, would have been to have the parallel L-C ckt tuned for 60 Hz. And if that cap were too large, it wouldn't tune, and the 60 Hz would go through it like cracked corn through a goose.
:
:Knowing that, personally I would experiment with a variety of film cap values, say starting at 0.05 uF and working up from there - seeing if I could find the one that best reduced the hum. (Even by jacking up the filter cap values, I presume there might be some residual hum?)
:
:It seems from looking at the differences between the Models 77 and 77A, Philco must have been battling hum complaints. The 77A has a larger cap across the power choke (0.45 vs. 0.15 uF). That implies to me that they also jacked up the inductance of the choke on the Model 77A? Do my proposed experiment, and report the results.
:
:Filter caps on early sets were often a bit skimpy. Before the advent of inexpensive, compact e-caps, radio manufacturers often used bulky, expensive, high-value paper caps. Ergo, the filter choke and its shunt cap for blocking the 60 Hz.
:
:I always hate going too far in jacking up the value of filter caps - because of the wear and tear they impose on rectifier tubes at start up. But maybe with the early 1930s sets, with skimpy filter caps, this is less of a concern?
:Doug
:
:
:
::Hi
::
:: I would agree with Doug's last statement, leave the cap out between #4 and #5 in the schematic. It's there to make a tuned circuit with the choke to reduce hum. This cap isn't needed when other filter cap values are increased. If not a fairly exact value this cap will actually increase hum.
::
::Norm
::
::
::
:::Here is the schematic: http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
:::
:::For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
:::
:::The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
:::
:::I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
:::Doug
:
:Doug
:
: Although I didn't see it written would expect 77A was made for 25 cycle operation. A lower frequency would require a larger cap value.
:
: Since this radio uses a full wave rectifier frequency of the tuned circuit would be 120 cycles and 50 cycles if the A version was made for 25 cycles operation.
:
:Norm
:
::Thanks, Norm, for explaining the purpose of that cap shunting the choke. The idea, would have been to have the parallel L-C ckt tuned for 60 Hz. And if that cap were too large, it wouldn't tune, and the 60 Hz would go through it like cracked corn through a goose.
::
::Knowing that, personally I would experiment with a variety of film cap values, say starting at 0.05 uF and working up from there - seeing if I could find the one that best reduced the hum. (Even by jacking up the filter cap values, I presume there might be some residual hum?)
::
::It seems from looking at the differences between the Models 77 and 77A, Philco must have been battling hum complaints. The 77A has a larger cap across the power choke (0.45 vs. 0.15 uF). That implies to me that they also jacked up the inductance of the choke on the Model 77A? Do my proposed experiment, and report the results.
::
::Filter caps on early sets were often a bit skimpy. Before the advent of inexpensive, compact e-caps, radio manufacturers often used bulky, expensive, high-value paper caps. Ergo, the filter choke and its shunt cap for blocking the 60 Hz.
::
::I always hate going too far in jacking up the value of filter caps - because of the wear and tear they impose on rectifier tubes at start up. But maybe with the early 1930s sets, with skimpy filter caps, this is less of a concern?
::Doug
::
::
::
:::Hi
:::
::: I would agree with Doug's last statement, leave the cap out between #4 and #5 in the schematic. It's there to make a tuned circuit with the choke to reduce hum. This cap isn't needed when other filter cap values are increased. If not a fairly exact value this cap will actually increase hum.
:::
:::Norm
:::
:::
:::
::::Here is the schematic: http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
::::
::::For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
::::
::::The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
::::
::::I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
::::Doug
::
Tubes which are gassy blue shouldn't be used. In time they can damage other parts of your radio. Some gassy tubes start drawing high current.
A tube is gassy when you see a blue/purple cloud within elements. If there is just blue just inside the glass, it's not a problem.
Using different caps or not having the .15 has no effect on gassy tubes.
Norm
:Ok I put in my 2.5 polys without the .15 across the choke. It warms up almost intantly with lower hum than before but the output tubes are gassy blue. Would that have to do with that .15 cap out?
:
:
::Doug
::
:: Although I didn't see it written would expect 77A was made for 25 cycle operation. A lower frequency would require a larger cap value.
::
:: Since this radio uses a full wave rectifier frequency of the tuned circuit would be 120 cycles and 50 cycles if the A version was made for 25 cycles operation.
::
::Norm
::
:::Thanks, Norm, for explaining the purpose of that cap shunting the choke. The idea, would have been to have the parallel L-C ckt tuned for 60 Hz. And if that cap were too large, it wouldn't tune, and the 60 Hz would go through it like cracked corn through a goose.
:::
:::Knowing that, personally I would experiment with a variety of film cap values, say starting at 0.05 uF and working up from there - seeing if I could find the one that best reduced the hum. (Even by jacking up the filter cap values, I presume there might be some residual hum?)
:::
:::It seems from looking at the differences between the Models 77 and 77A, Philco must have been battling hum complaints. The 77A has a larger cap across the power choke (0.45 vs. 0.15 uF). That implies to me that they also jacked up the inductance of the choke on the Model 77A? Do my proposed experiment, and report the results.
:::
:::Filter caps on early sets were often a bit skimpy. Before the advent of inexpensive, compact e-caps, radio manufacturers often used bulky, expensive, high-value paper caps. Ergo, the filter choke and its shunt cap for blocking the 60 Hz.
:::
:::I always hate going too far in jacking up the value of filter caps - because of the wear and tear they impose on rectifier tubes at start up. But maybe with the early 1930s sets, with skimpy filter caps, this is less of a concern?
:::Doug
:::
:::
:::
::::Hi
::::
:::: I would agree with Doug's last statement, leave the cap out between #4 and #5 in the schematic. It's there to make a tuned circuit with the choke to reduce hum. This cap isn't needed when other filter cap values are increased. If not a fairly exact value this cap will actually increase hum.
::::
::::Norm
::::
::::
::::
:::::Here is the schematic: http://www.nostalgiaair.org/PagesByModel/838/M0013838.pdf
:::::
:::::For the 2-uF caps, I would use the modern size, 4.7-uF, 450-V electrolytic caps. Available from www.tubesandmore.com. 10-uF caps should be OK, but I would prefer 4.7-uF, which should be adequate with the filter choke in the ckt.
:::::
:::::The original filter caps were presumably paper dielectric, non-polarized caps. But the replacement e-caps will be small enough to haywire under the chassis, leaving the filter block there if you wish. But disconnect the filter block terminals! Make sure you get the polarity of the replacement e-caps correct.
:::::
:::::I'm not real sure what the purpose is of the smaller cap between terminals 4 and 5, which shunts the filter choke (0.15 uF for the Model 77 and 0.45 uF for the Model 77A). I would go with a 0.47 film cap for that replacement. Being me, though, I would try the radio with and without that cap to see if there is a difference in hum - as an experiment.
:::::Doug
:::
Consensus is to use Mylar or poly caps, not electrolytics for those and use the same values.
You can read more about it on the PhilcoPhorum.
Syl
OK I have polys rated 2.5 mf at 330v and have electo's 6.8mf at 450v in my stock now. Should I go with polys for the sound or is the higher value in mfs a better performance choice? My peak volts from what I can see should not be over 230.
Yes. They will last indefinitely as opposed to electros. If you wish to up the capacity a bit use two caps in parallel. Try with one first. As long as the correct voltage is used.
Syl