Choke filter question

[catalin gramada]

Is not 20% but more than 100% between you expect and what is found as time a 5H 50cps rated, meant 2.5H at 100cps is real 7.5H in circuit. And yes I may do a effective difference in this situation. I don't talk about small nominal diferences in same circuit but big differences may occur due the comercial specs.

[Helmholtz]

Is not 20% but more than 100% between you expect and what is found as time a 5H 50cps rated, meant 2.5H at 100cps is real 7.5H in circuit.

Where/how did you see that much of a difference?
Inductance is not proportional to frequency.

As said earlier you need to measure/compare chokes under same AC and DC operating conditions.
I think Hammond gives useful data for filter application, though they only specify a minimum value.

[catalin gramada]

Inductance is not proportional to frequency.

You know better, I use on line reactance calculators. 2.5H /100 cps = 1.571 k vs 5H/50 cps=1.571k

[Helmholtz]

Are you mixing up impedance and inductance?

[catalin gramada]

Are you mixing up impedance and inductance?

No good ? I always calculate the ac attenuation by ac impedance raport. There is also some resistance indeed but negligible to count in respect with reactance of components. Get it wrong please ?

[Helmholtz]

Please answer my question of post #17.

[catalin gramada]

The diference comes from real tests with real 2.5H and 7.5H in same circuit. I have an open Hammond and setting the gap I may play with. But think you didn't get my point. I just put it as a newbie from a comercial perspective following this scenario : I want to build a clone or replace a choke shows in schematic as 5H for instance. You order a 5H dc choke supposing is rated for 100 (120) cps as time is called a DC reactor. But no it is rated for 50 cps. so you may expect to get a 2.5H dc reactor at nominal dc current considering impedance presented in circuit. This I want to point. What is the truth behind it tested in circuit is another story. The point I want to do is the comercial specs worth nothing as time they don't mentioned the conditions the reactors was measured. Still there are a lot of guys which plays with chokes making mods and found effective differences in sound from what was called 20% difference. I want to hear an opinion how can be made a choice when all are rated just like 4H 90 ma DC, for instance ? Then all discussions about Mercury vs Hammond or whatever makes sense because we don't know what is the real characteristics in circuit.

[Helmholtz]

Seems you're confusing a few things.
Doubling frequency does not double inductance, while it does double reactance/impedance with constant inductance.
As said earlier, higher frequency somewhat lowers effective inductance (mainly due to eddy currents), but the difference between 50Hz and 100Hz should be significantly lower than 20%.
I think Hammond data is quite useful.

I doubt anybody could "hear" a 20% difference in inductance or filter capacitance.(having essentially the same effect).
A lot of nonsense told on some internet forums.

Simplest way to compare chokes in an amp is measuring the AC voltage across the choke.

[catalin gramada]

Did a test at 100 and 50 cps at 87mA DC for a new Hammond 5H 150mA DC. Found 4.2H at 100 cps and 5.22H at 50cps... for 100cps found 41 VLac /14.45 VRac , for 50cps found 151 VLac/ 86 VRac. Of course to get same DC current over sense series resistor I had to raise the source voltage from 100Vac to 266V ac around.

[trobbins]

Would you be able to draw a diagram/schematic of your test setup please. It is not obvious to me how you supply dc current to the choke at the same time as ac is applied to it. A set of measured results across sense resistors would also help. Ta, Tim

[catalin gramada]

This is the simple jig test I done. Voltage measurements done with a dmm" true rms meter". No good ?

[Helmholtz]

To only see the effect of a frequency change, all other operating conditions must be the same.
I expect a major error from different voltage waveshapes.
(In fact impedance is only proportional to L for a single frequency sine.)

A 5H Marshall (Drake) choke measures 5.14H @100Hz, 5.08H @120Hz and 4.57H @1kHz on my LCR meter.
So frequency dependency is rather weak.

Manufacturers like Hammond might use something like this:
http://www.waynekerr.de/products_det...d=Wayne%20Kerr
(IIRC, we had one of those in our lab.)

[trobbins]

The choke will have a dc resistance - possibly around 200-300 ohm? The sense resistor (I think it says 937 ohm?) is noticeably more than the choke's dcr. The ac voltage across the choke is 86V, which is quite large, and much more than would be experienced in a typical CLC filter application, which may skew the actual inductance experienced in your application.

I can see that the 5.2H is measured for 50Hz, given the half-wave rectified dc being applied to the choke under test. How did you test for 100Hz - with a bridge rectifier instead of a single diode?

The meter has to be able to separately measure dc from rms. Not all meters do that, and some measure AC+DC as an rms.

The voltage waveform also needs to be fairly stiff. Are you using a special AC supply and variac, as the supply voltage is obviously more than 266V ?

[catalin gramada]

I have a question please. I did this circuit Circuit A supply the screen grids, B the preamp. With the circuit A alone the ripple is 50mV around but when connect circuit B the ripple is 1.6V. The same in reverse: if B circuit is supplied alone get 30mV ac ripple but when connect circuit A get 800mV ac. Why each lc works independent but mess when are connected both please ? There is a phasing problem or what ? Thanks.

[catalin gramada]

No it isn't, I reversed the wires and is the same. Thinking is not an usable configuration, but why please ? Thx.