Power transformer noise question

[Fuzzbuster]

Hello everyone. I recently picked up a 1960 Harman Kardon Stereo Recital receiver. Twice when I hit the power switch the power transformer made an odd noise. Only for a split second. It leads me to believe that maybe something downstream is drawing too much current on start up. At least this is what I'm hoping. I'd like to install current inrush limiters but have no idea where or how. Can anyone give me an idea of what's going on here? Thanks, Fuzz.

 

[mroboto]

What is the cunsumption of your receiver ?

I put one and sometimes two thermistors in series with the AC input socket Hot side

One on the socket and one on power switch.

The "Hot" side on input socketis is the thin narrow blade of the prong, not the large or round.

In other words, this is the side where when you hold the negative probe of tyour multimeter in AC mode in your hand (To put it at your own potential), and the positive the outside of one of the RCA inputs jacks, you have less AC measuring there, the side of the narrow blade in AC wall socket is at left when the round prong is upper, and at the right, you have the large blade, the neutral, don't touch to neutral, it must conduct perfectly.

For better performances, you should always connect as it should. mark one prong and remember wheer it should be on non polarised AC plugs.

PS:

I think you can add one or two CL-90 or NTC-120D15 120 ohms 1.8 or 2A thermistors.

Also, look at the transformer itself for mecanical tightening if not correct.

 

[century tek]

Its probably the laminates that are vibrating so its nothing I would worry about. My Magnavox 175 amps power transformer has a really loud buzz for the first micro second after powering on.

As long as its not over heating or smoking or blowing fuses, its fine.

 

[mroboto]

But thermistors are a safer way to start a switch, a transformer, heater, cathode, capacitor to hold, conduct, and dissipate current, as well as slow up the rising of high voltage in tubes..

 

[century tek]

Yup, you're right but the engineers didn't see any use for it so neither do I.

 

[Fuzzbuster]

What is the cunsumption of your receiver ?

I put one and sometimes two thermistors in series with the AC input socket Hot side

One on the socket and one on power switch.

The "Hot" side on input socketis is the thin narrow blade of the prong, not the large or round.

In other words, this is the side where when you hold the negative probe of tyour multimeter in AC mode in your hand (To put it at your own potential), and the positive the outside of one of the RCA inputs jacks, you have less AC measuring there, the side of the narrow blade in AC wall socket is at left when the round prong is upper, and at the right, you have the large blade, the neutral, don't touch to neutral, it must conduct perfectly.

For better performances, you should always connect as it should. mark one prong and remember wheer it should be on non polarised AC plugs.

PS:

I think you can add one or two CL-90 or NTC-120D15 120 ohms 1.8 or 2A thermistors.

Also, look at the transformer itself for mecanical tightening if not correct.

I have some CL-120 inrush limiters. They need to go in series with the hot side of the switch then?

 

[Fuzzbuster]

I just saw a diagram online that showed one on each leg of the A.C. Is that right?

 

[Fuzzbuster]

Ok...next question. This receiver uses a 4A fuse but the CL-120 is only rated at 1.7A. Should the Inrush Limiter be rated the same as the fuse?

 

[Edysusilo]

Its probably the laminates that are vibrating so its nothing I would worry about. My Magnavox 175 amps power transformer has a really loud buzz for the first micro second after powering on.

As long as its not over heating or smoking or blowing fuses, its fine.

+1

 

[mroboto]

The current must pass through the thermistor , you won't put one on the hot and one on the neutral, but the hot must enter one side and output the other side of the thermistor to or from the switch, or AC input outlet when there is one.

The CL-120 is only 10 ohms, while a CL-90 is 120 ohms , but 1.7-1.8A should be fine.

 

[Fuzzbuster]

The current must pass through the thermistor , you won't put one on the hot and one on the neutral, but the hot must enter one side and output the other side of the thermistor to or from the switch, or AC input outlet when there is one.

The CL-120 is only 10 ohms, while a CL-90 is 120 ohms , but 1.7-1.8A should be fine.

Thanks. I'll try it... certainly can't hurt.

 

[trobbins]

I'll try it... certainly can't hurt.

Given you don't know what the operating current of the receiver is, and may not have experience in installing a thermistor or with AC mains side wiring, then 'caveat emptor'.