Dropping Resistor?

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Dropping Resistor?

Post by nytuberadio on Sat Jun 18, 2011 1:30 pm

Looking at the schematic on the tube line up a 12BA6 could be used or a 6BJ6 as the RF amp.
In between the heater line up is a 3 watt 33 ohm resistor. With the 12BA6 in the line the ac voltages add up to a 114 volts without the drooping resistor. Do you still need the dropping resistor when the 12BA6 is used? I can see it is needed when the 6 volt tube is used because the string would only be up to 108 volts, but not with the 12BA6 is used.

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Re: Dropping Resistor?

Post by repairtech on Sun Jun 19, 2011 10:05 am

Assuming this is a series-connected AC/DC set, I'd leave the resistor as it should be.
It takes up excess surge voltage/current during warmup.

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Re: Dropping Resistor?

Post by zdiode on Tue Jan 03, 2012 12:19 pm

repairtech does have a point.
However, I have worked on Zenith H723 radios. These come in types with 6BJ6 and 12BA6 as the RF tube. H723's that have the 6BJ6 always have the resistor and H723 that have the 12BA6 never have the resistor.
My tendancy is to go with the Zenith engineers' design, however, repairtech does have a point. Reasonable persons can disagree on this.

All the Best,

Bill

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Re: Dropping Resistor?

Post by sprman on Sat Jan 07, 2012 6:55 pm

Yes leave the dropping resistor i place.They put it there to help keep voltage where they wanted it.Sprman

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