Scratch built 6G15 has issue

[tictac]

Am I tripping cause the view that I'm getting from the pictures you've posted is that you've got you're preamp tubes wired backwards! Looks like pin 1 has the green filament wire that would normally be connected to pin 9 connected to it. And what would from a layout point of view be pin 9 has a yellow wire going to a coupling cap!

TT

[tictac]

Sorry, I guess it was an optical illusion.... I knew I shouldn't have commented on....

too late.....


TT

[Blues Hound]

Update:

Traced the signal and the point where I am seeing a problem is at the 50k Tone pot lug that feeds the .1uf cap.

Trace is good when the pot is below 3, once you go over 3 the sine wave deformes at the peak, going from a smooth curve to very jagged.

Still not sure what is causing the PO, but it is there.

[Blues Hound]

Here are some pictures of the trace I am getting at the Mix and Tone pots.

Here id the 1kHz signal at lug 3 of the mix Pot

IMG_0387.JPG

Here the signal at lug 1 with the 250 pf cap going to the wiper of the the Tone pot, tone pot at 1

IMG_0388.JPG

Same location with the Tone pot at 4

IMG_0389.JPG

Same location with the Tone pot at 10

IMG_0390.JPG

[Blues Hound]

Well the unit is working very good at this point, added some passive components to it.

220k resistor and 2000pf cap across the footswitch jack, 1 meg resistor from Pin 2 of V1 to ground and .002 caps across the diodes of the full wave rectifier.

No longer feeds back when the Mix and Tone pots are turned up.

Thanks to everyone who chimed in...

Steve

[tubeswell]

...a problem is at the 50k Tone pot lug that feeds the .1uf cap.

This is the coupling cap from the reverb recovery stage. Did you try a different 12AX7 already? (I haven't bothered reading previous posts)

[Blues Hound]

Tubeswell, sorry for the late reply, haven't been online in a while...Yes, I had tried several new and NOS 12AX7's, currently has a Long Plate GE 12AX7 in it.

[tubeswell]

So it doesn't do this with the mixer control rotation all the way to 'dry' (I take it?). My guess at this point is distortion from the pan springs (in combination with a bit of Reverb transformer saturation and the single-ended reverb driver possibly not having any global NFB) - one way to tell would be to disconnect the pan's return cable and instead inject a 1kHz signal onto the grid of the reverb recovery stage and see if you still get this distortion. The way you've snubbed the rectifier diodes probably helps getting rid of diode-switching transients coming across the PT secondaries (after all is said and done, the reverb recovery stage is highly sensitive to S:N ratio, so the more you can eliminate extraneous noise sources, the more refined the listening experience will be)