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Old 30th May 2013, 09:30 AM   #101
Salas is online now Salas  Greece
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Classic symptom of oscillation. Changing the impedance and it changes.
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Old 30th May 2013, 09:46 AM   #102
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What happens if you parallel 220K across each 270K? Are they physically joined to the 47K in your build BTW?
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Old 30th May 2013, 10:12 AM   #103
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Hi. Not really. I found some, unfortunately low resolution pictures, on my physical planning layout. In the scetch, if we look at the right side the grid leaks are R19 (parallelled with a VR pot that I have now removed) and R20. The 47k is R21, directly to the lower 12AX7 grid.

The plate that I built it on is two 2-component glued hard paper with lead ears on.
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Last edited by stajo; 30th May 2013 at 10:15 AM.
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Old 30th May 2013, 10:48 AM   #104
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The 270k ones still refer to the node where the 47k and a 12AX7 grid refer. Does the 47k other side meet gnd along with the EL84s cathodes components?
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Old 30th May 2013, 11:01 AM   #105
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I'm at some negotiation table atm so I cant check but I have some connected ground pins in between the 12AX7s and as I remember it it goes directly to them, same as the EL84rs cathodes components. Grounds are channel separated (together with the last 47 uF C in the small signal filter) up to a leadstand that is between the circuit on one side and the OPTs and RCAs on the other side where all audiocircuits meet. That one has a 2 mm copper up to PSU ground.
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Old 30th May 2013, 11:11 AM   #106
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OK, just verify that those sections are following the schematic exactly for connections and then try to lower the 270k resistors value by // other values to see if a change can happen.
When you had a probe there it changed something, lets see what. Maybe a tighter and more symmetrical physical layout around those points will play a role even.
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Old 30th May 2013, 11:24 AM   #107
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I also wonder if there is an error in that schematic that shows no dots for nodes. What would happen if those 270k had gone to the 47k other side to ground for instance. But I did not spend time to analyze.
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Old 30th May 2013, 11:38 AM   #108
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It would change the balance in the Floating Paraphrase phase splitter is my humble opinion. The signal to the lower 12AX7 grid uses the EL84rs gridleak.
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Old 30th May 2013, 03:00 PM   #109
stajo is offline stajo  Sweden
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I just remembered, and verified passing by home briefly, that the "tighter and more symmetrical physical layout" was just what I tried last time I was trying to track this down. On pic (yes I know it looks like in closeup. It does when changing stuff alot) I have putted them all, two 270K and one 47K directly on the pin as experiment.

Salas, not that I mistrust your opinion about classic oscillation, but what was it that lead you to that? The very wiggle formation on the scope, the behaviour when I moved probe or the motorboating that starts when I simulate music by pushing different frequency buttons on gen?

Though.... I found on inspection that I for some layout reason has ca 15 mm wire left between my 1k Dale unmagnetic WW gridstoppers and grids.

Is EL84 that sensitive to grid oscillation? Experiences anyone?

Well I will try to shorten them later, but I dont have the time now.

Staffan
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Old 30th May 2013, 04:20 PM   #110
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When you touch (not in HV) or load a node that oscillates with some other impedance like a probe, it changes behavior or stops many times.
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