Choke inputs

[Tubeman777]

I am in need of some advice. In looking at various choices for rectifier, each tubes has specs for condenser input, or choke input. The choke inputs All require 4-10 Henry inductors, with a low value c1. My st70 has a one Henry inductor, does qualify as a choke input?

 

[TonyTecson]

no, it is not...

this one is...

 

[hangar18]

If the choke has a low value then the capacitor must have a higher value in oreder to form a RLC filter that will filter out AC ripple. So i'll say that indeed it is a choke input.

 

[Magz]

It's more accurate to talk about whether the circuit is "critical choke input" or not. This depends on the current, voltage and inductance. If the choke is of at least the critical inductance, you will have a critical choke input filter (lower voltage out, better regulation); if not, the filter will assume cap input properties (higher voltage out, poorer regulation).

Critical inductance (H) = Voltage (VDC)/Current (mA) is the Rule of thumb calculation.

.

 

[DF96]

with a low value c1

Where is "c1"? If small, at the rectifier output, and followed by a low value choke, then you really have a cap input supply formed by C2 (but preceded by a bit of smoothing).

 

[dirkwright]

(delete this part ->Well of course it's a choke input. There is no capacitor at the rectifier output, only the choke. It may not be a very good choke input power supply, but it's certainly of that type. Clearly, the design was intended to minimize space and cost. You can do better by installing a larger choke and filter capacitor, provided you have the room for it.)

(sorry, they drew the ST-70 schematic weird. It is a capacitor input after all.)

 

[SY]

Well of course it's a choke input.

The ST70 that the OP was asking about? No, it's definitely capacitor input (if memory serves, something like 40uF). You might have been misled by AJT's schematic, which was posted to illustrate what a choke input filter looks like.

 

[gingertube]

I have a number of chokes on the shelf which were sold as 2H 400mA chokes.
Is that 400mA the average DC current rating or peak DC current rating?

If it is average then they will do for nearly any power supply I will be designing, if its peak, then I can easily excede that 400mA value particularly on a choke input supply.

Cheers,
Ian

 

[dirkwright]

I assume it's the maximum DC current before saturation. You'd have to ask the manufacturer directly to get a more precise answer.

 

[Osvaldo de Banfield]

The value of the choke is inversely proportional to the load current. As the choke is only effective when it is not permitted to run dry, more inductance call for less load current, and vice versa. There isn't an absolute truth. See any book about the theme, ussually it is assumed that l [Amp] * L[Hy] is a constant.

 

[dirkwright]

A whole thread about this

Here you go:
http://www.diyaudio.com/forums/tubes-valves/159832-how-do-you-calculate-choke-size-power-supply.html

A search engine can be your best friend...