Silvertone 1906 Electrolytic Question from Newbie - Printable Version

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+--- Thread: Silvertone 1906 Electrolytic Question from Newbie (/showthread.php?tid=22202)

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Silvertone 1906 Electrolytic Question from Newbie - bobclausen - 02-21-2021

I’m attempting to restore a Silvertone 1906 and don’t want to mess up the electrolytic caps. The existing cap, a Mallory. I assume it is taking the place of C-20 and C-9, which were both 8 mfd caps.  I include a pic of how this electrolytic was wired. It shows the red wire connected to both ends of the cap. I was hoping someone could tell me why this was done and it’s purpose.

I am going to replace the Mallory cap with two separate 10 mfd caps but want to ensure I have the + and - connections connected properly. Any assistance would be appreciated. My confidence with wiring electrolytics correctly is such that I prefer to get advice from the Phorum. My schematic reading training is ongoing.

The last photo is a short red wire soldered to the cathode of tube 84. The other end has come loose. I can’t tell where the loose end used to be attached, and I can’t see anything on the schematic as to where this wire should go. Again...any advice is welcome.

I’m very new to the hobby, so I take no offense to any assistance.

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RE: Silvertone 1906 Electrolytic Question from Newbie - bobclausen - 02-21-2021

http://www.nostalgiaair.org/Resources/804/M0016804.htm

I forgot to post the schematic.

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RE: Silvertone 1906 Electrolytic Question from Newbie - Radioroslyn - 02-21-2021

Yes the two positive are connected together. The negatives are not and that's where the filtering is done. It's know as negative lead or leg filtering.

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RE: Silvertone 1906 Electrolytic Question from Newbie - MrFixr55 - 02-22-2021

Hi Bob,

RadioRoslyn has it right. I did not know that there was a name for it. This was a somewhat common way in the early and mid 1930s to wire the filter capacitors and choke (the speaker filed coil doubles as a choke. It was even done on the radiola 17, 18 and 60 (Ca 1927, 1928) It messed my head up a little when I first saw it, but do understand the reasons:
First, it may be for safety. Because the Speaker Field is on the low side, if it ever shorts, then the voltage to ground will be a lot less than the 250 - 350V if it was on the positive side of the supply.

Note also that the cathode of the 6F6 Audio Output tube is at chassis ground along with the negative lead of one of the filter capacitors.. the grid resistor is at the Power transformer center tap along with the negative lead of the other filter capacitor
The arrangement in the schematic provides negative bias without the need for a cathode resistor bypass capacitor. My Westinghouse WR217 has almost the same circuit. early RCAs such as my R7A Suprette also did the same thing. Hope this helps.

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RE: Silvertone 1906 Electrolytic Question from Newbie - bobclausen - 02-22-2021

Thanks Radioroslyn, I hadn’t seen that type of connection before and am always concerned with polarity when replacing electrolytics.

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