Field coil placement in a PS

[chopstuck]

Now I have an old TV front Pro I'm working on and got to thinking about the role of a high resistance FC in the power supply string.
In the 5A5 schematic it hangs off the first node to ground.
Does the coil have any effect on dc ripple here ?
I could put it in the PS designer but I don't have a way to measure the inductance.

Would it have any positive effect to place it at the second node to ground vs the first, after the plates ?

[Structo]

I'm lacking the 5A5 schematic.
Can you upload a copy?

From what I have seen most guys replace the field coil with either a choke or power resistor (10w).

[chopstuck]

Sorry, here it is.

I measured the DCR at 6k. So I think my Flot-A-Tone is a good match for the 5A5.

I'm pondering using a connector maybe from an old organ harness (if I haven't tossed them all.)

I'm just worried about hard-wiring the the whole shebang.

[Structo]

Of course they don't list the spec of the FC!

I know when we were all building D'lites we used 300R-500R power resistors instead of chokes.
Later I added a choke, didn't really notice any difference.

[gingertube]

With high DCR Field Coils wired between B+ and 0V then it doesn't matter much where you connect it. It is not like the lower DCR types which are wired in series with the B+ and form a power supply choke as well.

You said you measured 6K DCR. With a B+ of say 400V then yoyu will have about 7ma of current through the field coil. Filtering at the B+ point shown has 2 x 24uF so will be adequate. No real point in shifting it to the output tube screen supply point, only 24uF extra filtering and the series resitor would have to be adjusted for the additional 7mA current draw.

I would ONLY consider changing it IF the sag in the B+ line on attack is causing too much compression from the speaker due to similar sag in field coil current and hence magnetic field. I doubt this is the case.

Cheers,
Ian

[surfsup]

With high DCR Field Coils wired between B+ and 0V then it doesn't matter much where you connect it.

If the resistance is 6k, wouldn't 70mA go through it, not 7mA?

400v/6000r = 0.066A = 66mA

Also if it is moved further down the rail, each power rail resistor between it and the rectifier will drop more voltage, or cook from the heat.[/i]

[gingertube]

Er yes. Slipped a digit.
approx 70mA is correct, more reason to leaver the connection exatly where it is shown in the schematic posted above.

Thanks for correcting my maths slip.

Cheers,
Ian

[printer2]

The inductance of the speaker should have minimal impact on the load the power supply sees because the voltage is constant (other than the ripple where the inductance does come into play) so the current through the coil is determined by the coil's resistance.

[chopstuck]

Thanks for the replies.

I will leave it alone.

[chopstuck]

Posted repair as new topic