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In Reply to: RE: traces at last.... posted by vinnie2 on October 24, 2016 at 09:12:00
Looking at the last trace, that works out to approximately 2.5V p-p amplitude (.1V/div X 2.5 divisions X x10 probe). The large peaks in the last trace are about 3.25 divisions apart horizontally, or 16.25 mS. The inverse of that is ~ 60 Hz. There's also considerable 120 Hz energy. I don't see anything else happening, such as oscillations.
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Buy Chinese. Bury freedom.
Follow Ups:
2.5V P-P at the output terminals with the speaker attached?
So that means I have way to much ac getting through the filters of the psu, right?
What part of the picture shows the 120 hz? Could it be the 120 hz that is causing the small buzz I hear?
Vinnie, the 120 Hz energy is visible in the form of smaller peaks that fall in-between the 60 Hz energy. They're also occurring "underneath" the 60 Hz peaks, but being masked. This could all be caused by a number of things, and maybe more than one. Generally speaking, 60 Hz can be picked up from the PS magnetics or from the surrounding environment. 120 Hz might be from the PS filter or filament doubling (my 211s did that). If you want to probe the B+, you'll need a high-voltage probe. However, a simpler method is to model the PS in either PSUD or SPICE. If you know all the characteristics of the components in the power supply, the simulators will be very close to real world. 2.5V is quite a lot of ripple, so I suspect this is occurring in an early stage and being amplified.
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Buy Chinese. Bury freedom.
Edits: 10/24/16
If it isn't in the psu, it might be coming from the rats nest huh? I may have to wait until I clean things up with the final build before I can get rid of it.
I did model the ps in psud2 before I put it together and I just did it again after double checking the schematic against what is out there. I have a 1500 vct trans with 3 1N4007 diodes in series off each leg going to the first 8H choke. There is an 87 uf cap between that and the next 8H choke and then another 87 uf cap with a 20 ohm/50w resistor across it. When I run this in psud2 I get what looks to me like only about .003 volts (3mV right?). That should be ok shouldn't it?
Edits: 10/24/16
vinnie, without changing anything else, move the switch under the volts/div knob for channel 1 to AC and snap a photo.
It was already in the ac position. I moved it to the ground position and it changed to a flat line, and then I moved it to dc and got exactly the same trace as in the ac position. I then switched the probe to channel 2 and got exactly the same results. I have a feeling you guys are going to tell me that is not what should have happened. : )
Right - the output should be AC only. If you are in GND, then you just get a flat line: this position is there so you can use your vertical adjust to put that one one reference grid. If you had then, let's say 2.5v DC AND your AC signal, putting on DC would make the trace shift up by one division (2.5v) - essentially a combined AC and DC volt meter.
If you have the input shorted then your original posted wave is the results of all the odd artifacts added by your amp because, what I don't think has been posted, is that when the input is shorted, the output should (ideally) be a flat line: no AC, no DC. I agree with someone who suggested this is from the heater arrangement you have.
In a DHSET, you will likely NEVER have a completely flat line, but should be closer than what you have. If you move the time base to a faster and faster time, you may see those spikes become their own little sign waves on top of the dominant sign wave - an oscillation.
By the way, I don't know where you live, but I'm in the Portland, OR area and have the same scope. Happy to walk you through in more detail.
'thanks for the post. I am in NC, so there is a bit of country between us. The videos are helping a lot, so I hope to get the hang of it. Not sure what you mean by the heater arrangement I have; is there a better way to do it?
He doesn't need to do that. There's no DC on the secondary of the OPT.
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Buy Chinese. Bury freedom.
I thought he was on the other side. never mind.
Then how come it shows an ac curve in the DC position on both channels?
Vinnie, the scope merely inserts a series blocking cap in AC mode. If there's no DC on the point you're analyzing, moving the switch from AC to DC won't make any difference.Edit: The results you reported above are exactly what should happen.
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Buy Chinese. Bury freedom.
Edits: 10/24/16 10/24/16
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