10-14-2026, 06:59 AM
Hi Roy,
I don't believe that you need a Y2 cap for C12 but definitely use a Y2 for C11.
The purpose of safety caps is for the cap to be able to handle continuous current (Caps conduct AC) but also to be able to handle voltage spikes to a defined level. The difference between X2 and Y2 caps is that X2 caps fail shorted and Y2 caps fail open. Ironically, X2 caps are placed across the power inputs, so when they short, they will either blow a fuse or smoke a switch, itself or whatever (However, ai believe that they are supposed to be fireproof. This is the reason that any cap that goes between power line and chassis as part of filtering must be a Y2 cap in order to keep the chassis from becoming hot.
On a transformer powered set, caps are usually placed between Line and Chassis and Neutral and Chassis to filter out common mode noise. The reason for safety caps in this case is that these caps are essentially in series across the power line with the chassis at the "halfway point". You will actually feel a "tickle" when touching an ungrounded transformer powered chassis. Therefore, Y2 caps are used for both caps. This should be the case for your RCA 6K3
However, it is different on an AC-DC transformerless "warm chassis" set. In your Silvertone, you can use an X2 cap if you fuse the power line, as this cap is across the power line after the switch. Most folks, however, use a Y2 cap for this cap. AC-DC sets are generally not fused as the heater of the rectifier acts as the fuse in most cases. In your set, a short across the B+ supply would take out the 35Z5 heaters, the pilot and the 150 Ohm resistor, so yeah, definitely put in a 0.5A fuse.
C12 is not meant as a noise filter cap. In an AC-DC set, the purpose of this cap is to provide a path from B- / Common (The return for both the B supply and the heater string back to the power line) and the chassis for high frequencies while providing sufficiently low leakage current to prevent electrocution if a person contacts the chassis while the B- / Common is connected to the "Line" of the outlet. ("Line" is that current carrying conductor which is 120V above earth ground. "Neutral" is that current carrying conductor that is at earth ground potential). Therefore, it is not carrying the current that a cap across the power line is carrying. There is certainly no harm in using a Y2 cap for this cap, and in theory it would be safer, but since there is no "hard ground" connection to the chassis (External grounds are not connected to the chassis on a transformerless set), no current is carried by C12 and spiking should not affect it.
The bigger issue is the power switch in the "Common" as opposed by the hot. This was done by radio manufacturers from the time if first introduction of transformerless sets to the end of the tube era. I believe that the theory was that if the switch was in the neutral, there would be less hum introduced into the audio, as the power switch is usually attached to the back of the volume control. However, this creates a condition where the chassis can become hot (or warm) despite the position of the power cord. For example, if a polarized cord is installed so the "Line" (or "Hot") connects to the rectifier input and "high" side of the heater string, but the switch is in the neutral, the set is safe with the power switch on but with the switch off, the chassis becomes hot (or warm) due to the very low resistance of the tube heater string when cold. Therefore, I think that it is a good idea to do so.
It is important to note that most transformerless chassis are "warm" (cap between Common and chassis, but several are "HOT," including most late 1950 Zenith AM radios, most radios on PC boards and most transformerless AM / FM radios, for example, the RCA 8X71 and many Zenith tabletop models.
Sorry for the length of this, especially if you are already aware of all of this but I write with the idea that folks new to this hobby will read a thread between experts looking for knowledge.
The one instance where changing the location of the power switch from Neutral to Line will not create a safer condition is transformerless sets that use a full wave voltage doubler. There will always be a voltage between chassis and neutral. This is not the case with half wave voltage doublers.
This link is to an excellent article by Phillip Nelson of "Phil's Old Radios" on this issue:
Improving Safety and Reliability of AA5 Radios
I don't believe that you need a Y2 cap for C12 but definitely use a Y2 for C11.
The purpose of safety caps is for the cap to be able to handle continuous current (Caps conduct AC) but also to be able to handle voltage spikes to a defined level. The difference between X2 and Y2 caps is that X2 caps fail shorted and Y2 caps fail open. Ironically, X2 caps are placed across the power inputs, so when they short, they will either blow a fuse or smoke a switch, itself or whatever (However, ai believe that they are supposed to be fireproof. This is the reason that any cap that goes between power line and chassis as part of filtering must be a Y2 cap in order to keep the chassis from becoming hot.
On a transformer powered set, caps are usually placed between Line and Chassis and Neutral and Chassis to filter out common mode noise. The reason for safety caps in this case is that these caps are essentially in series across the power line with the chassis at the "halfway point". You will actually feel a "tickle" when touching an ungrounded transformer powered chassis. Therefore, Y2 caps are used for both caps. This should be the case for your RCA 6K3
However, it is different on an AC-DC transformerless "warm chassis" set. In your Silvertone, you can use an X2 cap if you fuse the power line, as this cap is across the power line after the switch. Most folks, however, use a Y2 cap for this cap. AC-DC sets are generally not fused as the heater of the rectifier acts as the fuse in most cases. In your set, a short across the B+ supply would take out the 35Z5 heaters, the pilot and the 150 Ohm resistor, so yeah, definitely put in a 0.5A fuse.
C12 is not meant as a noise filter cap. In an AC-DC set, the purpose of this cap is to provide a path from B- / Common (The return for both the B supply and the heater string back to the power line) and the chassis for high frequencies while providing sufficiently low leakage current to prevent electrocution if a person contacts the chassis while the B- / Common is connected to the "Line" of the outlet. ("Line" is that current carrying conductor which is 120V above earth ground. "Neutral" is that current carrying conductor that is at earth ground potential). Therefore, it is not carrying the current that a cap across the power line is carrying. There is certainly no harm in using a Y2 cap for this cap, and in theory it would be safer, but since there is no "hard ground" connection to the chassis (External grounds are not connected to the chassis on a transformerless set), no current is carried by C12 and spiking should not affect it.
The bigger issue is the power switch in the "Common" as opposed by the hot. This was done by radio manufacturers from the time if first introduction of transformerless sets to the end of the tube era. I believe that the theory was that if the switch was in the neutral, there would be less hum introduced into the audio, as the power switch is usually attached to the back of the volume control. However, this creates a condition where the chassis can become hot (or warm) despite the position of the power cord. For example, if a polarized cord is installed so the "Line" (or "Hot") connects to the rectifier input and "high" side of the heater string, but the switch is in the neutral, the set is safe with the power switch on but with the switch off, the chassis becomes hot (or warm) due to the very low resistance of the tube heater string when cold. Therefore, I think that it is a good idea to do so.
It is important to note that most transformerless chassis are "warm" (cap between Common and chassis, but several are "HOT," including most late 1950 Zenith AM radios, most radios on PC boards and most transformerless AM / FM radios, for example, the RCA 8X71 and many Zenith tabletop models.
Sorry for the length of this, especially if you are already aware of all of this but I write with the idea that folks new to this hobby will read a thread between experts looking for knowledge.
The one instance where changing the location of the power switch from Neutral to Line will not create a safer condition is transformerless sets that use a full wave voltage doubler. There will always be a voltage between chassis and neutral. This is not the case with half wave voltage doublers.
This link is to an excellent article by Phillip Nelson of "Phil's Old Radios" on this issue:
Improving Safety and Reliability of AA5 Radios
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
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