Supro 1690T build

[dbishopbliss]

I'm following with this schematic, so;
Supro_1690t.pdf (el34world.com)

IF the mix point for dry signal and trem is a cathode and has a bypass cap, (like the linked schematic), lift it n test.

Yep, that's the one. I will give it a try tomorrow. Today is a busy day.


Another thing I need to try is swapping the 15K resistor off of the foot switch for a 6.8K. That is what Leon C has in his amp and was marked as a variant on that schematic. Although, I bypassed it entirely with some of Sluckey's suggestions so I can't imagine that would make a difference. Leon C also said he has a 3.3uF cap in parallel with the .001 cap. I tried clipping in a 2.2uF because that is the closest I have but it didn't make a difference.


I got some time to play at full volume for about 2 hours yesterday. The amp sounds great and there is a slight barely noticeable change in tone when the tremolo is engaged. And there is a loud pop when the switch is engaged. So something is happening. Just no whump whump whump.

[Willabe]

At this point, I'd change the tube socket and the wires that go to it.

We have seen more than a couple times, someone could not fix the amp and out of desperation they changed the tube socket and that was it.

You have nothing to lose at this point.

[martiro7]

Apologies for jumping back into this topic after a couple years, but my own 1696t build is nearing completion and I just wanted to share a couple of items I encountered, dbishopbliss.

1.) My tremolo was annoyingly subtle. The end result, following sLuckey's comments, was to remove the 1K cathode resistor on V3b and replace it with an LED. Steve does this in his Supro Model S-6424 (12/10/2020). Like magic, the tremolo is now loud and proud! Highly recommended.

2.) On first power up, I also blew my 33uF 50V cathode bypass cap in the power section. I ended up replacing it with a 160V cap for extra insurance. Glad to hear your 50V cap is doing the trick.