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« on: September 02, 2023, 12:19:48 AM »
Hi:
I've just completed a second 503J unit which works as it should and if it were not for the fact I have a unit built from last year, I would maybe know no better. Activating the DIST switch bypasses to ground R12 (4.7M). But, when in tube mode, there is a difference between the Old and the New unit characteristics.
With the DIST switch activated, the new build sucks out more of the high frequencies - muffling the sound compared to the old version (otherwise they are identical in sound). The schematic is the same for both units but I noticed that C6 is a 100V cap in the new build compared to a 63V cap in the old but that shouldn't matter. I checked the DIST switch grounding etc and its all good and the unit is working as it should other than the DIST difference. It was a bit of a challenge to set the 50K TR1 pot with the DIST activated on the new dull sounding build. I swapped over the tubes between units but there is no difference in performance. Voltages on the tube stages are all more or less identical.
What would cause this and how can I get the new dull sounding unit to behave as the old one? Is it tolerances on C6?
Regards
Craig