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diyAudio Member

Join Date: Mar 2011
Location: Jarna
Quote:
 Originally Posted by stajo So while Im puting for Ikos measure here, whats the local poll: fiddling filaments finding op points with B+ 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.

 29th April 2013, 08:53 PM #2132 diyAudio Moderator     Join Date: May 2008 Location: Toronto 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.
 29th April 2013, 10:12 PM #2133 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece 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.
 29th April 2013, 10:38 PM #2134 diyAudio Member   Join Date: Mar 2011 Location: Jarna 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 .
diyAudio Member

Join Date: Jun 2011
Location: Stockholm
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
 scope 6V6 001 (3000x2000).jpg (873.8 KB, 225 views) scope 6V6 003 (3000x2000).jpg (763.6 KB, 209 views) PSUD (725x685).jpg (143.0 KB, 178 views) scope 6V6 009 (3000x2000).jpg (662.1 KB, 168 views) scope 6V6 010 (3000x2000).jpg (696.5 KB, 154 views) scope 6V6 015 (3000x2000).jpg (695.3 KB, 38 views) scope 6V6 017 (3000x2000).jpg (740.1 KB, 34 views) scope 6V6 018 (3000x2000).jpg (695.1 KB, 33 views) scope 6V6 019 (3000x2000).jpg (690.2 KB, 34 views)

 1st May 2013, 08:23 AM #2136 diyAudio Member     Join Date: Sep 2006 Location: Wallis Blog Entries: 1 Cool __________________ RC
 1st May 2013, 09:47 AM #2137 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece Scoping at 2mV/div and not even filling a graticule. But from 4 to 8-9 you can understand there is some 50Hz introduced.
 1st May 2013, 01:57 PM #2138 diyAudio Moderator     Join Date: May 2008 Location: Toronto
 1st May 2013, 04:44 PM #2139 diyAudio Member   Join Date: Jun 2011 Location: Stockholm
diyAudio Chief Moderator

Join Date: Oct 2002
Location: Athens-Greece
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.
Attached Images
 Arb.jpg (475.3 KB, 49 views)

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