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Old 29th April 2013, 08:33 PM   #2131
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Quote:
Originally Posted by stajo View Post
So while Im puting for Ikos measure here, whats the local poll:
  1. fiddling filaments
  2. finding op points with B+
  3. decoupling chokes with a small zobel
What would be your first shot?
Setting the op point for the tube first.

Then you test some different tubes.

When you find a nice pair finetune the filaments.
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Old 29th April 2013, 08:53 PM   #2132
iko is offline iko  Canada
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If you look at that picture, you will see that the spike at 50Hz is somewhere around -53dB. Let's assume this is relative to 0dB = 1V. To calculate how many volts -53dB is relative to 1V, you do 10^(-53/20) = 2.2mV. So, at 50hZ you have a ripple of about 2.2mV RMS = 2.2*sqrt(2)*2 = 6.22mV p-p. In Arta you can click the mouse on the spike and then use the lef-right arrow buttons on the keyboard to measure more precisely how many dB the spike is at its highest point. You can calculate like this the mV value of the ripple for the other harmonics as well, 100hZ, 150hZ, etc.

Suffice to say, you have more ripple than what you should have from the HV shunt regulator.
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Old 29th April 2013, 10:12 PM   #2133
Salas is online now Salas  Greece
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That FFT is on the audio output. It represents everything circuit in there. Why is it just rail ripple? Where was that ripple on the rail scope test? Hum is 50Hz ripple is 100Hz. But 100Hz is -90dB there. The spray of harmonic noise is too wide to be just ripple on the rail of a buffer at line level IMHO. If feeding B+ with just CRC I am not sure that the picture would change much. And such a test could easily eliminate rail related questions or point at the PSU side indeed so to move on investigating. I would bet more on oscillation of the reg on the choke than just ripple if it is coming from the rail. There is suspicious microphony reported also, I would investigate instability or loop area issues regarding the choke loading next.
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Old 29th April 2013, 10:38 PM   #2134
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Start with a basic resistor load and get the thing up and running properly first.

Chokes have a nasty habit of picking upp every unwanted signal there is.

Split the PSU from the amp getting rid of any AC near the amp.

I“ve got nice shielded industrķal power cables come and get them Stajo.

After that you can start investigating the amp for grounding and stability issues.

Now there“s so many factors involved .
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Old 1st May 2013, 08:14 AM   #2135
stajo is online now stajo  Sweden
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Howdy. Its a kind of holliday here and I woke up early so what to do if not play around with new scope.

Yesterday I made a conversion of the choke loaded CF to a resistor loaded and listened and measured. (Pic 1) About the same looking Arta curves and a small hum plus audiable noice in speakers. I also tried to feed it directly from PSU filter, without SSHVs. Small differences regarding hum and noice but the 305 V on the anodes sure made music glare.

So, today I made some scoping on the power rails. First up is PSU filter on 13,5 k/channel dummyload. (Pic 2). Around 5 mV p-p (1,8 mV rms) which I think is to much for this config. Should be less if the measuring tools doesnt add something.

I made a sim in PSUD II that says 127 uV (Pic 3)

Then I set the SSHVs on same dummyload (Pic 4). 5 mV/div so now we are down to measuring tolerances but occasionally I also noticed small occational spikes on the scopescreen. Very hard to catch on camera but you can see a shadow on Pic 5. Then a view on the same with 2 mV/div (Pic 6).

For some reason SSHV V in looks more stable then when the bare PSU loads a resistor dummyload (pic 7).

After that I removed dummyload and plugged in the reconverted choke loaded audio circuit. Pic 8 on the anodes, 2 mV/div, and Pic 9 on cathodes.

I guess this takes a coffee, some reference measuring and more

Attached Images
File Type: jpg scope 6V6 001 (3000x2000).jpg (873.8 KB, 159 views)
File Type: jpg scope 6V6 003 (3000x2000).jpg (763.6 KB, 150 views)
File Type: jpg PSUD (725x685).jpg (143.0 KB, 125 views)
File Type: jpg scope 6V6 009 (3000x2000).jpg (662.1 KB, 120 views)
File Type: jpg scope 6V6 010 (3000x2000).jpg (696.5 KB, 112 views)
File Type: jpg scope 6V6 015 (3000x2000).jpg (695.3 KB, 24 views)
File Type: jpg scope 6V6 017 (3000x2000).jpg (740.1 KB, 19 views)
File Type: jpg scope 6V6 018 (3000x2000).jpg (695.1 KB, 21 views)
File Type: jpg scope 6V6 019 (3000x2000).jpg (690.2 KB, 21 views)
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Old 1st May 2013, 08:23 AM   #2136
RCruz is offline RCruz  Switzerland
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Old 1st May 2013, 09:47 AM   #2137
Salas is online now Salas  Greece
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Scoping at 2mV/div and not even filling a graticule. But from 4 to 8-9 you can understand there is some 50Hz introduced.
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Old 1st May 2013, 01:57 PM   #2138
iko is offline iko  Canada
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Old 1st May 2013, 04:44 PM   #2139
stajo is online now stajo  Sweden
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Filterchoke and transformer, EMI-experiment - YouTube
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Old 3rd May 2013, 11:39 AM   #2140
Salas is online now Salas  Greece
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So that was just filter chokes moving about or load chokes do it too? Lots of loop area and inductance makes fields easy to pick in general. Now if you will be able to create something like this out of just interference you are in for the next Nobel prize.
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