There are two #44 pilot lamps on the 6.3 volt line connected parallel to the 6.3 volt line and after all of the tube filaments. Now the schematic is showing a 0.4 ohm resistor wired in series with the lamps presumably to protect the lamps from power surges and maybe to help control current drain on the 6.3 line?) But I have looked everywhere on the chassis and there is no sign that there ever was a 0.4 ohm resistor! I'm thinking that the 0.4 ohm "resistor" is actually a reference to the resistance of the connecting wire that was used.
When I measure the resistance across the installed 6.3 volt transformer secondary the reading is about 0.5 ohm with the pilot lamps in place but with none of the tubes in their sockets (my meter can barely read resistance this low). Should I be concerned about this resistance reading and is it a good idea to place a small resistor in series with the pilot lamps?
:I'm restoring a 5 tube set with a power transformer. Four of the tubes have 6.3 volt filaments and the rectifier has its own 5 volt transformer secondary. The 6.3 volt transformer secondary is not center tapped and one side of the 6.3 volt line is grounded directly to the metal chassis. Now where I'm going with all of this is that I'm concerned about the very low resistance measurements on the 6.3 volt line.
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:There are two #44 pilot lamps on the 6.3 volt line connected parallel to the 6.3 volt line and after all of the tube filaments. Now the schematic is showing a 0.4 ohm resistor wired in series with the lamps presumably to protect the lamps from power surges and maybe to help control current drain on the 6.3 line?) But I have looked everywhere on the chassis and there is no sign that there ever was a 0.4 ohm resistor! I'm thinking that the 0.4 ohm "resistor" is actually a reference to the resistance of the connecting wire that was used.
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:When I measure the resistance across the installed 6.3 volt transformer secondary the reading is about 0.5 ohm with the pilot lamps in place but with none of the tubes in their sockets (my meter can barely read resistance this low). Should I be concerned about this resistance reading and is it a good idea to place a small resistor in series with the pilot lamps?
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: The resistor is probably meant to lengthen bulb filament life. You may want to add one if it blows lamps. The resistor may have been added as a 'running change' due to short lamp life complaints.
: Cold filament 'turn on' resistance will be low and is the cause of the initial current surge that blows lamps.
: Once the filaments are warmed, resistance rises (current lowers) and stabilizes.
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::I'm restoring a 5 tube set with a power transformer. Four of the tubes have 6.3 volt filaments and the rectifier has its own 5 volt transformer secondary. The 6.3 volt transformer secondary is not center tapped and one side of the 6.3 volt line is grounded directly to the metal chassis. Now where I'm going with all of this is that I'm concerned about the very low resistance measurements on the 6.3 volt line.
::
::There are two #44 pilot lamps on the 6.3 volt line connected parallel to the 6.3 volt line and after all of the tube filaments. Now the schematic is showing a 0.4 ohm resistor wired in series with the lamps presumably to protect the lamps from power surges and maybe to help control current drain on the 6.3 line?) But I have looked everywhere on the chassis and there is no sign that there ever was a 0.4 ohm resistor! I'm thinking that the 0.4 ohm "resistor" is actually a reference to the resistance of the connecting wire that was used.
::
::When I measure the resistance across the installed 6.3 volt transformer secondary the reading is about 0.5 ohm with the pilot lamps in place but with none of the tubes in their sockets (my meter can barely read resistance this low). Should I be concerned about this resistance reading and is it a good idea to place a small resistor in series with the pilot lamps?
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:Thanks Walter. I didn't think about the resistance change from cold to warmed up filaments but what you suggest makes complete sense. I believe that my set was an earlier production and the schematic that I'm using probably reflects final production changes. I will definitely install that 'mystery' resistor!
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:: The resistor is probably meant to lengthen bulb filament life. You may want to add one if it blows lamps. T1 he resistor may have been added as a 'running change' due to short lamp life complaints.
:: Cold filament 'turn on' resistance will be low and is the cause of the initial current surge that blows lamps.
:: Once the filaments are warmed, resistance rises (current lowers) and stabilizes.
::
:::I'm restoring a 5 tube set with a power transformer. Four of the tubes have 6.3 volt filaments and the rectifier has its own 5 volt transformer secondary. The 6.3 volt transformer secondary is not center tapped and one side of the 6.3 volt line is grounded directly to the metal chassis. Now where I'm going with all of this is that I'm concerned about the very low resistance measurements on the 6.3 volt line.
:::
:::There are two #44 pilot lamps on the 6.3 volt line connected parallel to the 6.3 volt line and after all of the tube filaments. Now the schematic is showing a 0.4 ohm resistor wired in series with the lamps presumably to protect the lamps from power surges and maybe to help control current drain on the 6.3 line?) But I have looked everywhere on the chassis and there is no sign that there ever was a 0.4 ohm resistor! I'm thinking that the 0.4 ohm "resistor" is actually a reference to the resistance of the connecting wire that was used.
:::
:::When I measure the resistance across the installed 6.3 volt transformer secondary the reading is about 0.5 ohm with the pilot lamps in place but with none of the tubes in their sockets (my meter can barely read resistance this low). Should I be concerned about this resistance reading and is it a good idea to place a small resistor in series with the pilot lamps?
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The light bulbs are in parallel with the tube filaments. With the resistance of the tube filaments being low at turn-on, their current draw will be excessive, and will load down the 6.3V supply, reducing the voltage. The bulbs will glow more dimly at turn-on than they would once the set warms up, as is the case in any other radio with parallel-wired filaments.
If anything a resistor might have been added to dim the bulbs slightly to make them last longer all-in-all, but there are no excess voltage surges to protect them from.
T.
:??????????????????
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:The light bulbs are in parallel with the tube filaments. With the resistance of the tube filaments being low at turn-on, their current draw will be excessive, and will load down the 6.3V supply, reducing the voltage. The bulbs will glow more dimly at turn-on than they would once the set warms up, as is the case in any other radio with parallel-wired filaments.
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:If anything a resistor might have been added to dim the bulbs slightly to make them last longer all-in-all, but there are no excess voltage surges to protect them from.
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:T.
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T.