Heaters/Filaments, Centre Taps and Current Draw

[Andy Le Blanc]

Ohms laws needs two figures to solve for the third.

current in series is figured like you would capacitance

so if you had two 6sl7 in series at 12.6 v . each has a current rating of .3 a

I tot. = I1 x I2 / I1 + I2

.3 x .3 / .3 + .3 = .09 / .6 = .15 a

which is expected, but it works for mixed values and gives you one more
bit of info to work Ohms laws with.

[gearhead]

Ohms laws needs two figures to solve for the third.

current in series is figured like you would capacitance

so if you had two 6sl7 in series at 12.6 v . each has a current rating of .3 a

I tot. = I1 x I2 / I1 + I2

.3 x .3 / .3 + .3 = .09 / .6 = .15 a

which is expected, but it works for mixed values and gives you one more
bit of info to work Ohms laws with.

Is that right? Two tube heaters drawing 300 mA of current each should total at leat 300 mA, no matter where they are placed (series or parallel). With a constant impedence (ohms) for each, the voltage might vary tho.

[paulster]

Would it be possible to put a 40 ohm/1 watt resistor in parallel with the 6111 heater, and have each heater getting its correct current and voltage?

I've just done the calculation and that's right.

The voltage drop across the 5902 and the parallel 6111/resistor would then be the same, i.e. 6V.

[frequencycentral]

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[Andy Le Blanc]

Its an introverted proponent, (sorry), inverse proportion.
A 12ax7 is rated parallel, 6.3v 0.3 a, and series 12.6v 0.15a.

Is the opposite from series/parallel with resistance or say figuring speaker impedance. With two 8 ohm in series is 16 ohm. and two 8 ohm parallel is 4 ohm.

[frequencycentral]

.....

[gearhead]

Its an introverted proponent, (sorry), inverse proportion.
A 12ax7 is rated parallel, 6.3v 0.3 a, and series 12.6v 0.15a.

That makes much more sense. Each heater draws 150 mA and drops 6.3V. Mix and match to get those values.

Is the opposite from series/parallel with resistance or say figuring speaker impedance. With two 8 ohm in series is 16 ohm. and two 8 ohm parallel is 4 ohm.

Volts/Amps are electrical energy attributes, versus resistance/capacitance, which are component attributes.

For resistors:

If components (resistor) are in series, the current is the same through each component, and therefore the same at the entry-exit point of the component network.

If the components are in parallel, the current is distinct for each one. The total at the entry-exit point of the component network is a summation of all the individual component currents.

If components are in series, the voltage is is distinct for each one. The total at the entry-exit point of the component network is a summation of all the individual component currents.

If the components are in parallel, the voltage across each is the same for each one, and as for the group as a whole.

[Andy Le Blanc]

A very old common practice for AC/DC sets and TV's, was to string all the heaters to
ground with the most sensitive (noise) valves at the ground end, and make up
the difference between the volts needed to light the filaments and the line voltage
with a resistor, in the set or in the power cord, but you need an Amps (I) to
make ohms law work to find R. Wouldn't mind trying out 50L6 as power tubes
and series heaters in a guitar amp, but the voltage conditions from the power
company varies so wildly, it might not be practical.

[Wayne]

A very old common practice for AC/DC sets and TV's, was to string all the heaters to
ground with the most sensitive (noise) valves at the ground end, and make up
the difference between the volts needed to light the filaments and the line voltage
with a resistor, in the set or in the power cord, but you need an Amps (I) to
make ohms law work to find R. Wouldn't mind trying out 50L6 as power tubes
and series heaters in a guitar amp, but the voltage conditions from the power
company varies so wildly, it might not be practical.

You might be on to something, Andy. Have you priced NOS 50L6s?

W

[Andy Le Blanc]

Less than $10 per unit. (retail)

[Andy Le Blanc]

This could be a very convenient way to go.
Two 50l6 which draw .15a at 50v
And two 12ax7 dressed in series draw .15a at 12 v
which add up to be 124v string with a .0375a
In my area the line is as high as 128 so the make up resistor or adjustment
pot. is around 100 ohms.
It would use a silicon rectifier. The low current restricts choice there.
Ill have to double check the math but it looks appealing.

[Wayne]

Even if you had to build a dedicated heater supply (separate xfmr, DC through some goofy voltage doubler scheme, or whatever), you can't beat that price for vintage...


I'll shut up now - Let's keep this our little secret!

W