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I'm attempting to repair a Clarion C104 tube radio. I started the repair years ago, put it away, and now I'm giving it another attempt. When I started the repair, the transformer (Clarion part no. C80-223) was damaged, so I replaced it with an equivalent transformer (Hammond Manufacturing part no. 270DX). clarion transformer Hammond transformer Transformer windings

Unfortunately, several of the transformer wires have become disconnected between then and now, and I'm attempting to reconnect them correctly.

I understand that many tubes use a heater voltage of 6.3V--thus the 6.3V output on the Filament #2 winding. However, the Sam's PhotoFacts schematic for this radio seems to show the Filament #2 winding disconnected:

Sam's Schematic

I'm assuming that the lower winding in the schematic is Filament #1 since the 5Y3GT rectifier tube has a filament voltage of 5.0V: 5Y3GT Spec

Why does this radio leave the 6.3V tap disconnected?

In asking that question, I'm making assumptions. Perhaps these questions need to be answered first:

  • Am I correct in interpreting the stub on the upper tap of the transformer in the PhotoFacts schematic as indicating that it's disconnected?
  • Why did they ground the other leg of the upper tap if the entire tap is unused?
  • Why are there two loops on the 5.0 V tap in the PhotoFacts schematic and one loop on the 6.3 V tap? Shouldn't it be the other way around? Did I misinterpret which tap is which?
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    \$\begingroup\$ That looks like it might be an arrow-head on the end of that transformer tap, which I would be inclined to interpret as something along the lines of "we all know where this goes and we don't want to clutter up the schematic by drawing it in everywhere." \$\endgroup\$
    – brhans
    May 7, 2019 at 15:05
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    \$\begingroup\$ @brhans Ah. OK. Looking at the schematic again, I see that pin 7 (one of the heater pins) on every other tube has no connection on the schematic. Perhaps it goes there. \$\endgroup\$
    – watkipet
    May 7, 2019 at 15:09
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    \$\begingroup\$ @StainlessSteelRat did you read brhans comment - valves (tubes) don't work without heaters! \$\endgroup\$
    – Chu
    May 7, 2019 at 16:24
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    \$\begingroup\$ @brhans Please make your comment into an answer. It's 100% correct. \$\endgroup\$
    – TimWescott
    May 7, 2019 at 16:35
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    \$\begingroup\$ @StainlessSteelRat Heaters provide the electron cloud that's fundamental to tube operation, either directly or by heating a cathode, they are not optional. Omitting their connections on circuit diagrams was as commonplace as not showing the power supply lines on op-amp circuits today. \$\endgroup\$
    – Chu
    May 7, 2019 at 16:45

2 Answers 2

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That looks like it might be an arrow-head on the end of that transformer tap, which I would be inclined to interpret as something along the lines of "we all know where this goes and we don't want to clutter up the schematic by drawing it in everywhere."

So in this instance, I believe that you're intended to connect that tap on the transformer to all of the heater filaments.

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  • \$\begingroup\$ Would it be safe to say that, "we all know this goes to the tube filaments", given that this is a schematic for a tube radio? Or is it better to leave that conclusion as an exercise for the reader of this question / answer? \$\endgroup\$
    – watkipet
    May 7, 2019 at 21:17
  • \$\begingroup\$ Since every heater (OK except the rectifier) has one grounded pin and one unconnected, this is certainly the answer. \$\endgroup\$
    – user16324
    May 7, 2019 at 21:19
  • \$\begingroup\$ @brhans I'll accept your answer either way, but do you think your answer would be better if you added that this is the heater connection for the rest of the tubes? \$\endgroup\$
    – watkipet
    May 7, 2019 at 21:32
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The "arrow" symbol is an Earth/Ground symbol. It means that all of those points are connected to a (common) ground. On an old radio, the "common ground" is probably the steel chassis frame: if there is no metal chassis frame, it would be wired: in modern electronics it would have to be a pcb track and pour:

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  • \$\begingroup\$ I really don't see how this is an answer to the question. The "arrow" that is refered to in brhans's answer is not the "ground" arrow you seem to refer to (which would be pretty obvious for anyone familiar with electronics), but the (thin) arrow that's at the end of one of the transformer taps in the schematic. \$\endgroup\$
    – StarCat
    Nov 21, 2021 at 9:23

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