[morzh]

The piec of equipment that causes 95% of he noise is in my workshop and is nothing other than the USb 5V DCDC they put right into the power strip. and the light is connected to it also. So, when I work, the light is on, but when aligning, I have to turn it off and only use the ceiling light.
One day...one day I will open that strip and YANK that stupid USB converter outa'there.

[Kurt P]

My problem child was the power supply to the fume extractor, it’s new and somehow I just didn’t think of it as a possible offender, lesson learned!

[MrFixr55]

It's funny how switchers can wreak such havoc but they are the power supply for so much modern electronics, especially audio and sensitive instrumentation amplifiers.

I have 2 very cheap 120V power sources that put out a "modified sine wave" (stacked square wave) output. I tried to run an AA5 set on it to no avail, the noise even with the volume control was horrid. Tried an AC only transformer powered AM set with a full wave rectifier, and the results were much better, with minimal hash

After an issue with 2 ChiKrap 14.4V batteries that I used in my field audio mixer and wireless mic rig to power the 2 wireless mic receivers dying in the middle of a religious service, I decided to use the 20V Dewalt batteries for the wireless mic receivers. Since the receivers are supposed to run on 12-15V, I used a DC-DC convertor that was designed for cars to put out 13.8V with an input from between 8 and 30V. This would allow me to use either the 2 decent 14.4 V batteries or 2 of the 20 V Batteries. The batteries go to diodes to act as a block that if one battery dies or shorts, that it does not drain the other battery. Despite the fact that the DC-DC inverter is essentially a switcher, its output is clean and NO interference to the audio system is noted. However, I have not placed an AM radio next to it.

[RodB]

Mike, isn't that against the law? You could probably burn it but yanking it out will get you in trouble! ;-o

[morzh]

Kurt

A power supply to a fume extractor?
I have a Hakko one. A fan and a carbon filter.
Why does it need a power supply?

[Kurt P]

My main one is a larger unit that doesn't hum and I position over my work. The noise offender is a smaller cheap orange Kotto extractor that I leave over my iron and Hakko solder sucker. It isn't strictly necessary but I have it so I leave it on since I'm always adding waste solder to my iron to keep the tip healthy...

[morzh]

Hmm...I have a Hakko solder sucker. Need to test it. Though, this one needs not to be kept on except for the actuall moment when you need to sock the solder.

[MrFixr55]

There IS some 120 Hz sine wave on the trace, therefore you do have some power supply hum. You can bump up the caps some. However, raising the capacity raises the voltage and raises the load on the rectifier tube. You can try up to 30 uF after the filter choke but don't go to high on the cap before the choke, especially if using a vintage (globe) rectifier. Keep it 20 uF or less.

I have 2 theories here. Others with more EE experience than I do, please chime in:

Electrolytic caps were a relatively new invention in the early 1930s and were of the "wet" type and making caps with values higher than about 10 uF was expensive. And the early 1930s was NOT a time for expensive. Newer sets, especially post war sets used caps as high as 30 uF or sometimes even higher, as high as 40 uF. Please note that although the RCA Receiving Tube Manual Ver. RC14 (1940) states that the type 80 has the same specs as the 5Y3 that replaced it and at the time of publication the 80 was a 5Y3 with a 4 pin base, this tube likely has ratings much higher than the original 80 which relied on caps no higher than 4uF and chokes 20 Henries or higher to keep peak current down. Therefore, although by 1940, for cap input filters, RCA was specifying a max input cap value of 40uF, I don't think that an 80 made before 1940 would withstand the current caused by a 40 uF cap.

The other theory is that the cap input filter that used a choke and 2 caps (The speaker field served as a choke in many sets) constituted a "Pi" filter and therefore functioned almost as a tuned circuit.