03-17-2021, 08:45 PM
Hi Steve,
If no one has posted answers to your last questions:
The volume and tone controls are usually 1/2 watt. The volume control likely should be 500K Ohm, or 1 Meg Ohm, and importantly, "Audio Taper". A 100K Ohm should work for the Tone Control if yours is bad. You can measure between the 2 end connections to get an idea of the actual resistance. Try cleaning them before replacing them. Caig DeoxIT ™ is popular among a lot of experts.
The Candohm Resistor is represented by the "string" at the top right of the Rider's Schematic for the radio. It is a rather clever voltage divider for both "B" and "C" (bias) voltages. It is important to get the resistances in the correct Order. From B+ to center tap of the transformer (C-, based on the fact that the center tap is more negative than chassis ground, common in radios of this vintage) is:
11 KOhm, 4940 Ohm, 920 Ohm, 83 Ohm, 74 Ohm, 250 Ohm. 5 Watt wire wound ceramics would be fine, and may be overkill for some of these. a 5 Watt for the 11K Resistor and 3 Watt metal film for the rest of them should be OK. You will likely not get exact values for these resistors. If the error is 5% or less, there will be no issue. For example, substituting a 5 KOhm resistor for the 4940 Ohm resistor is an error of about 1.2%
Note that the diagram calls the resistance closest to the junction of the field coil and B+ to the Audio Output stage is listed as 11M. This is confusing but M in this context on schematics of this vintage is the same as Kiloohm, KOhm or Ohm x 1000. For resistances in the Megaohm range, Megaohm or Meg is the usual marking on schematic of this vintage.
I welcome the comments of the experts as to my recommendations. Any difference of opinion, please take the recommendations of the experts and moderators over mine.
There is one other recommendation that I have. I do not remember where I saw this but considering adding a 1N1007 Rectifier between each leg of the Power transformer and the Plate of the 5Y3 Rectifier with the cathode (band end) connected to the plate and the other end to the transformer. This will protect the transformer if the rectifier tube shorts. Filament heater type tubes like the 5Y3, 80, etc. can short filament to plate if the filament opens. This happened to me as a kid on a nice Philco console (Can't remember the model, but must have been early post war because the older ones had a Heater style cathode in the rectifier tube, such as 84 and 7Y4 types). Filled the house with smoke and stink from a burning power xformer and Mom freaked. She made me put it right out to the curb, Dad knew what happened but wisely demured to Mom. He knew that discretion was the better art of valor.
Good luck on your restoration!
John "MrFixr55
If no one has posted answers to your last questions:
The volume and tone controls are usually 1/2 watt. The volume control likely should be 500K Ohm, or 1 Meg Ohm, and importantly, "Audio Taper". A 100K Ohm should work for the Tone Control if yours is bad. You can measure between the 2 end connections to get an idea of the actual resistance. Try cleaning them before replacing them. Caig DeoxIT ™ is popular among a lot of experts.
The Candohm Resistor is represented by the "string" at the top right of the Rider's Schematic for the radio. It is a rather clever voltage divider for both "B" and "C" (bias) voltages. It is important to get the resistances in the correct Order. From B+ to center tap of the transformer (C-, based on the fact that the center tap is more negative than chassis ground, common in radios of this vintage) is:
11 KOhm, 4940 Ohm, 920 Ohm, 83 Ohm, 74 Ohm, 250 Ohm. 5 Watt wire wound ceramics would be fine, and may be overkill for some of these. a 5 Watt for the 11K Resistor and 3 Watt metal film for the rest of them should be OK. You will likely not get exact values for these resistors. If the error is 5% or less, there will be no issue. For example, substituting a 5 KOhm resistor for the 4940 Ohm resistor is an error of about 1.2%
Note that the diagram calls the resistance closest to the junction of the field coil and B+ to the Audio Output stage is listed as 11M. This is confusing but M in this context on schematics of this vintage is the same as Kiloohm, KOhm or Ohm x 1000. For resistances in the Megaohm range, Megaohm or Meg is the usual marking on schematic of this vintage.
I welcome the comments of the experts as to my recommendations. Any difference of opinion, please take the recommendations of the experts and moderators over mine.
There is one other recommendation that I have. I do not remember where I saw this but considering adding a 1N1007 Rectifier between each leg of the Power transformer and the Plate of the 5Y3 Rectifier with the cathode (band end) connected to the plate and the other end to the transformer. This will protect the transformer if the rectifier tube shorts. Filament heater type tubes like the 5Y3, 80, etc. can short filament to plate if the filament opens. This happened to me as a kid on a nice Philco console (Can't remember the model, but must have been early post war because the older ones had a Heater style cathode in the rectifier tube, such as 84 and 7Y4 types). Filled the house with smoke and stink from a burning power xformer and Mom freaked. She made me put it right out to the curb, Dad knew what happened but wisely demured to Mom. He knew that discretion was the better art of valor.
Good luck on your restoration!
John "MrFixr55
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
