heater Voltage too high

Tube or solid-state, this section goes to eleven!
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contobruto
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Post by contobruto »

I bought a chassis from ebay really cheap to be my first tube project,
ebay link basically the power transformer is kicking out too high Voltages. the guy selling it said B+ needed dropped (using a 470R 10w after the rectifier diodes) I measured the voltage on mine and got 430v, so have left that for the minute...... the problem I have is the heater secondary is 8.5v and needs dropped I was told on PPwatt.com that two resistors of 0.33r or 0.47r would drop it down to an acceptable range , I tried placing 1 resistor in series with each wire but the measured voltage after this was the same as before, so how is it done? Im obviously missing something basic here :roll:

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Aharon
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Post by Aharon »

Did you measure with the tubes in or out?.

Aharon

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contobruto
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Post by contobruto »

measured with tubes out, but its still too high surely? it should be @ 6.3

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Aharon
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Post by Aharon »

I would measure under load and see how much it is.
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Goop_buster
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Post by Goop_buster »

Voltage cannot drop over those resistors when there is no current flowing.

Ohm's law is probably one of the most basic and the fundamental things you should know about, perhaps especially when playing around with high voltage :wink: .
I am not trying to be offensive here but please be carefull. There is some very real danger if you not know enough.

You cannot calculate the optimal size of those resistors without testing the heater winding under load (all tube heaters or equivalent current ) and knowing the total amount of heater current needed.

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contobruto
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Post by contobruto »

no offense taken, thanks for the information...onwards and upwards :D

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