Filament Power, for larger builds

[Cqwet Dbdfte]

Right, the ground loop problem may need to be solved one way, RFI in another way. When these old texts were produced cell phones wasn't a major issue. Many "balanced" lines are not truly differential, just DC balanced. Ethernet lines have a good setup for differential signalling and transformer isolation. Stranded CAT 5/6 should work ok also for audio.

 

[ruffrecords]

Sadly, Muncy's '94 AES paper isn't easily findable free online. It is exceptional.

There are different schools as to best practices for what to do with the shields. Up to and including landing one end and connecting the other through a small cap for RF. Always sounded like a pain to me.

A place I worked 25 years ago was set up with male end lifted, bussed shields, if landed, at the bays. Mic lines excepted. Still had noise issues. I redid quite a bit of stuff there this last year, some fairly guerilla, two rooms very conventional. Landed everything, bussed at the bays, and have had virtually no problems (one issue with the monitors on a TSM aside). Don't ask me what changed. The place was built in the 70s, and redone several times since. Oddly, it seems to work best like this. Just goes to show that "ground loops" aren't always ground loops. Nowadays, I tend to land, and lift if I have problems. I find relatively few.

I once found an interesting paper years ago, I think by Clive Green of Cadac. Bottom lines, the more screens you can parallel by landing both ends, the lower any noise becomes. Basically the interference current has less impedance across which to create an interfering voltage.

e
But again, a whole different animal to the pin 1 problem.

Indeed.

Cheers

Ian

 

[smgear]

Ignorant newb questions back to the DC issue. Pardon the basic questions, but I'm trying to wrap my head around these concepts. I've had good success using the 12v meanwell when using only 12v tubes, and used a 50V supply to replace a selenium rectifier in an old Grommes that was series dividing to four 12v tubes. The latter seems like a risky approach to me.

I'm looking for some 6.3v solutions for a couple projects that will only work with 6.3v tubes. I can't find any switching supplies that can provide that out of the box. Using a 12.6v supply can power two in series and the meanwell 15v can be adjusted to 18, which is on the low side, but probably sufficient for running 3 tubes. But I'm assuming there could be issues if the current draw between dissimilar tubes is significantly different, as well as the inherent issue of a failed heater along the line.

Alternatively, I've considered running two 3v power supplies in series. But I'm wondering if that might cause problems with the regulation circuitry or be otherwise inadvisable.

I've been reading different threads on methods to elevate, boost, or buck 5v or 7.5v supplies, but most of the suggestions appear to add instability or noise. So what do you guys recommend for a 6.3v DC supply?

Thanks!

 

[emrr]

I've used a Meanwell 7.5 volt that would adjust downward some. I used diode drop to get part of the way, only practical for lower loads.

 

[smgear]

That makes

I've used a Meanwell 7.5 volt that would adjust downward some. I used diode drop to get part of the way, only practical for lower loads.

That makes sense. Most of the stuff I'm working with is fairly low load, but I'm perhaps overcautious about blowing something up.

 

[Cqwet Dbdfte]

Series connected heaters need equal current rating, else the voltages will not divide equally between tubes.