simple se inrush limiter placement

[pforeman]

On another link I found that it is recommended to have a inrush limiter in line with the on / off switch,fuse, as well as a second in series with the center tap high voltage winding. Is this the
RED/YELLOW wire from the Power Transformer?, and can I connect it right to the screw terminal on the circuit board?
Thanks,
Paul

[ChrisA]

Originally posted by pforeman
On another link I found that it is recommended to have a inrush limiter in line with the on / off switch,fuse, as well as a second in series with the center tap high voltage winding. Is this the
RED/YELLOW wire from the Power Transformer?, and can I connect it right to the screw terminal on the circuit board?
Thanks,
Paul

I read the same and I've been trying to understand how one on the PT's center tap can work. These things need current to heat up. What is the expected steady state current at that location? I don't think that thermistor there will ever warm up.

[Doc Jr 8156]

You are correct. The ICLs are corrected on the hot side and to the center tap of the high voltage widing (red-yellow). However, I noticed that with the thermistor in the center tap, upon powering up, I can hear a short crackle from my 95db speakers once the 5Ar4 kicks in. Did anyone noticed this too? Godspeed.

John Revilla

[chrish]

I have not noticed any crackling on power up at all. I retro fitted my inrush current limiter, and only did it on the centre tap of the HT. The centre tap is the return for the full HT current, around 150-180mA.

Regards,

Chris

[rknize]

+1 and ditto. I have one CL90 on the hot side of the primary and one on the center tap. I never got around to putting the third on the primary neutral.

Like Chris said, the center tap is the return for both side of the winding when using a "full wave" rectifier (two diodes). When using a bridge rectifier (four diodes), the center tap is typically not used unless a split supply is being created.

[scott17]

I understand using a CL90 on the PT primary side, but on the transformer center tap I'm not sure how the CL90 would work if the steady state B+ current is only 150mA or so. The datasheet shows the minimum current to be 500mA. Even the CL140 needs minimum 200mA to operate, according to the datasheet.

Is there another part# that is recommended when used in series with the secondary CT? I haven't been able to locate one for 150mA.

Scott

[ChrisA]

Look at these. Inrush Current Limiters - Power Thermistors - Ametherm They make some small ones. But more importantly, they will answer questions and give free samples. I got a couple dozen from them as samples after exchanging emails with one of their engineers.

But I think for such low power as 150ma you can design the system so there is little in-rush. Sometimes the resistance in the secondary is enough or maybe if you add a small fixed resistor in series

[scott17]

Originally Posted by ChrisA

Look at these. Inrush Current Limiters - Power Thermistors - AmethermSometimes the resistance in the secondary is enough or maybe if you add a small fixed resistor in series

Hey thanks for the reply. I'll check those out.

I'm using an EH 5U4GB, and I haven't had an ongoing problem. My PT meets the minimum secondary resistance requirements and the first cap is 30uF. After testing a few of the EH rectifiers I found one that will arc once on power up and then will be fine. Strange thing is that the PS is designed to bleed off when powered down, and it does. Even if I power it off for a day and then turn it on, no arc, and the rectifier works fine. Only if the rectifier is removed from the socket and then re-inserted does this arc happen. Maybe it's a suspect tube, but it only does this once after being installed and powered up. Weird right?