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In Reply to: RE: Is this feasible? Rectifying 6.3v for heaters posted by Tre' on December 08, 2017 at 13:59:15
...Try setting it to +/- 10V and superimpose a 6.3VAC RMS waveform on the spikey DC waveform.Edit: I really doubt a practical low voltage supply designed to deliver more than a few mA would be half wave as you simmed. Full wave would be a lot more representative of something that would actually get built.
Edits: 12/08/17Follow Ups:
It's clearly labeled.
It shows about .65 volts peak to peak and it shows the wave shape of the ripple.
That much sawtooth ripple will cause a grinding buzz. 6.3vac would only cause a slight hum that can be mitigated by layout and a hum pot.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
In my experience a little sawtooth ripple "sounds worse" than a lot of sinusoidal ripple.
but hey, I could be wrong.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I know what follows will change no minds but....I put together a real-life circuit representing your sim: 6.3VAC/6A transformer, 3A/40PIV schottky, 6.8mF filter cap and 100mA avg DC load.
Output: 8.5VDC, 64mV RMS ripple, 225mV PP ripple
Pics of scope:
Ripple waveform with scales adjusted to emphasize apparent nastiness of it similar to what you posted:
Ripple waveform with original 6.3VAC superimposed, both at same scale:
AC output of 6.3VAC transformer with hipass filter and 70mA AC load:
All things considered, I'd take the DC with a little bit of sawtooth ripple over the noisy, 100% ripple power line source for heating an IDH tube hands down. And this is with far less than optimum half wave rectification. Others may choose differently for a variety of technical and aesthetic reasons.
Edits: 12/10/17
I'm sorry. I got lost. What are we looking at here?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
...riding on the basic basic 60Hz waveform. The proliferation of smps, cfls, leds and dimmers has added a lot of hf junk to the power line that gets thru even an EI core transformer. A toroid transformer would be worse.
Could you clarify as to why a toroid would be worse?
Thanks.
"Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon
Unless special measures are taken, the frequency response of a toroid PT is generally much better than an EI cored transformer. The extended HF response couples more HF junk on the primary to the secondary. The HF performance of many toroid PTs is extended enough that they have been successfully repurposed as PP tube OPTs.
Somewhere on the Asylum is a quote from John Curl, from many years ago. He says that he never used toroids in preamps because of the noise, and would only use them in power amps.
Your explanation makes that clear as to why, and where the noise is coming from.
Thanks Steve.
"Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon
Pictures are nice but pictures with scales are meaningful.
dave
I didn't consider scales for the first two pics nec since they were intended to show relative magnitudes. However, scales are implied by info in explanatory text. 0.2 or 0.5 V/div for last pic. Purpose of last pic is to show what appears on the sec of a typical filament transformer supplying AC current to a purely resistive load and is not intended to be absolutely objective.
the first two pictures are shown in relation to each other and I agree the absolute numbers do not matter. The third one is an ugly waveform but more info on how you got that info and the time scale would be helpful. You say you high passed the signal but is that just the remnants of the 60hz left showing all the artifacts that remain?
Showing this with the original waveform on the same scales for reference like you did for the first one would be a good way to show the relationship.
I find this similar to zooming in on the frequency sweeps of a circuit. Here is the frequency response of a simmed LCR phono stage.
Of course I used the oldest trick in the marketing book to make it look Ruler flat. Now take the same info and show it in a more revealing light and dear god we have one of the most nonlinear circuits ever seen.
The second you peek a little more to the right in the plot it suddenly becomes clear that the variation is only +- 0.1dB and the world is a safe place again.
I guess this was just a long way to make my point that an ugly picture doesn't reaally tell us anything unless all of the surrounding data is documented with it.
dave
I've deconstructed the test set up so I can't provide a "superimposed" shot as you suggest. However, recall that the vertical scale on the "noise" shot was 0.2 or 0.5 V/div so a full display of 6.3VAC would overwhelm the noise component. Nevertheless, if you look carefully at the sine wave in the superimposed shot I posted, you can see the distortion in it at the max and min. IOW, the mains waveform is clearly distorted even when viewed at full scale.
To produce the last shot, I constructed a 1st order passive RC hipass with a time constant ~ 100uS. Since this is a simple filter, there's still a lot of 60Hz present at the output as you can see.
I guess we all need power conditioners these days.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Those higher harmonics are a bitch.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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