2023 Monkeymatic Whitney (Deluxe Reverb)

[xtian]

I'm building my first AB763 Deluxe Reverb, using the excellent PCB from Andrea. Hammond iron. Mojotone chassis and custom cabinet (on order). Jensen N12K speaker.

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[pompeiisneaks]

Looks nice! I've still got to build my ODS from the board by Andrea that was donated to me Lazy guy lately....

~Phil

[xtian]

Well, crap--Mojotone says their DR chassis won't be available until end of December! Anyone have a chassis for me?

[xtian]

I ordered a chassis from eBay--just had to search "blackface chassis."

[Reeltarded]

Beautiful board. Rikens would really be great for a blues amp.

I am terrified by your search term. Al Jolson videos on YT for 6 months. Good luck.

Those boards look excellent!! I have a SF Super that has a Leslie kit that needs modernizing. I think you just found my next project!

[ViperDoc]

That board looks awesome. My last PR I built using blue Sozos and Hammond iron with great results. Looking forward to hearing what you think.

[xtian]

Parts mounted in chassis.

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Those yellow PCBs on the tube sockets are from Lou, and highly recommended: https://luigiretro.com

[bepone]

sorry, correction, NOT recommended.
you had originally between the pins on the socket air, and it is fine. now you put porosive PCB which is worst in any terms than air.. also clearance is not so good. octal socket will draw high cureent heater line through very thin pcb film? so for future realiability problems just remove those pcbs and proceed without..

[xtian]

Build finished. But I'm having a weird problem. After tubes warm up and start conducting, I get a loud, high-pitched tone. Positive feedback, right? The strange thing is, swapping the OT primaries has no effect! Disconnecting the gNFB solves the problem. Maybe this is because my NFB wire runs adjacent to the other OT secondary wires that I have coiled up and taped off. I'll have to experiment with that. Any other ideas?

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[xtian]

More confused. Still getting feedback, even with NFB removed! Pulling PI tube makes noise stop. I moved my OT wires, no change.

[Guy77]

More confused. Still getting feedback, even with NFB removed! Pulling PI tube makes noise stop. I moved my OT wires, no change.

I had this happen once with an amp that had reverb. It turned out I had positioned my tank too close to the speaker magnet.
Unplugging the tank made the feedback noise go away. I ended up repositioning the tank in the combo and that solved the issue.

Cheers
Guy

[xtian]

Thanks, Guy. Turns out the issue was a bad JJ 6V6, right out of the box!

Next, must figure out why my fancy RCA jacks aren't grounded to the chassis. And then will need to audit my grouding scheme--this new PCB is nice, but unfamiliar, and I may have introduced a ground loop.

[xtian]

Much better. I fixed my RCA jacks (I had put the ground lugs on the wrong side of the washers, so they were not making good contact with the RCA jack bodies. Now that that's solved, the hum I was hearing is gone, so no ground loop issues. Nice and quiet. Reverb is lush and excellent!

Only issue remaining is with the vibrato. It kicks in immediately when I ground the vibrato pedal jack, but the oscillations ramp down quickly, over two or three seconds, and then the oscillation is no longer audible. Repeats each time I ground the vibrato jack. Why won't the oscillation stay strong? I tried two 12AX7s in that position. Any ideas?

[xtian]

Regarding the vibrato fading out, here's another clue for you RC-time-constant Wizards. If I set the Speed to slowest, and engage the vibrato, I can hear about 10 cycles before the effect fades away. If I set the Speed faster, the same number of cycles is audible, but faster.

[sluckey]

Is the oscillator cathode resistor 2.7K? Kinda looks like an 820Ω if I'm looking at the right resistor. Can you post your layout?

EDIT... Pretty sure I was looking at the wrong resistor. Still need to verify that V5 pin 3 connects to a 2.7K and a good 22µF bypass cap. Really shooting in the dark without a layout.

Also, what value caps are you using for the three oscillator caps?