Rectifier rolling (cont)

[nre]

I apologize for continuing a thread from another forum.  At page 3, about half-way down, I show (05 November) a series of measurements, voltage and in-rush current for a 5AR4 rectifier tube and 2x1N5408 rectifier plug-in module using the clone 299C amplifier.  That thread is here: 

https://community.klipsch.com/index.php?/topic/212772-rectifier-rolling/page/3/#comments

The effect of an in-rush current limiter, in this case a CL-90 (2A max) is shown below.  First photo show peak in-rush current at switch turn on with the CL-90 on the hot side of the AC line.  The rectifier is the 2x1N5408 solid-state plug-in.  A reading of 0.96A is evidenced using the CL-90.  Compare to the same measurement without the in-rush current limiter (second photo) of about 2.57A.

A significant difference.

Third photo shows in-rush current limiter patched (cobbled?) into AC line.  Once the CL-90 comes to temperature the current draw is consistent with no in-rush limiter (last photo) of about 1.5A.

The meter is an early Fluke 87.  The in-rush current is measured using the Fluke current interrupt patch cord, 100ms recording length, recording peak current draw.   

[Travis In Austin]

How do you like a post? Like this thread, I might learn something here, but it takes a lot for some of this to sink in.

Travis

[nre]

but it takes a lot for some of this to sink in.

Perhaps the three schematics below will make it straightforward.

The first shows the power supply that I'm using with the tube rectifier, a 5AR4.  The Fluke meter has one side of the power supply transformer primary winding passing thru it, this is how the current is measured.  The Fluke can capture current data in either a 1ms time interval (1/1000 sec) or 100ms (1/10 sec).  Inrush current is a transient phenomenon and occurs at power supply turn on.  By setting the Fluke meter to 100ms recording length, a reading is taken every 1/10th sec with a few mA precision, what's needed for this measurement.

The second shows the tube replaced by the solid-state rectifiers and the third shows the addition of the CL-90 thermistor in the circuit. Think of a thermistor as a power resistor, in this case, with a resistance that decreases the hotter it gets.

In the first case, the "cold load" (think of it as a short circuit that lasts for 10s of ms) presented to the power supply transformer secondary doesn't pull much current from the wall socket (thru the transformer primary) because the tube rectifier needs a few seconds to come up to emission temperature hence there's a gradual current pull. 

In the second case, at turn-on the solid-state rectifiers are on instantaneously and the power supply will attempt to source current immediately.  The cold load behaves as a short and the power supply works into it causing a very large current draw. 

In the third case, at turn-on the solid-state rectifiers are on instantaneously but the thermistor is cold and has a very high resistance which throttles the current until it gets hot and its resistance drops to a fraction of an Ohm.  The thermistor turns the current draw from the wall into heat.

[nre]

How do you like a post?
Travis

I'll have to get back to you on this!