My take on a 2nd Gen ODS

[ijedouglas]

Looking good!

[Raoul Duke]

Great progress Matt! Looks fantastic, probably sounds even better

[martin manning]

Wired up the power supply today to do a preliminary smoke check before proceeding any further... Powered it up slowly with my variac and current limiter.
No smoke, pops, or blown fuses.
B+ values were around what I would expect for an unloaded amp running through a current limiter.

Nicely done. So, all four power supplies (heaters, 12V relay, bias, and high-voltage DC) up and working properly?
When you drop the main board in, are you planning on getting the power amp up and working as your next test?

[Matt J]

Wired up the power supply today to do a preliminary smoke check before proceeding any further... Powered it up slowly with my variac and current limiter.
No smoke, pops, or blown fuses.
B+ values were around what I would expect for an unloaded amp running through a current limiter.

Nicely done. So, all four power supplies (heaters, 12V relay, bias, and high-voltage DC) up and working properly?
When you drop the main board in, are you planning on getting the power amp up and working as your next test?

Thank you!
Yep, proper DC was measured on everything, with the current limiter and without. Nothing burned or started to get a smokey smell. I'm going to repeat the same test this evening just to double check everything.
Correct, I'm going to slowly bring everything up on my variac again once the main board is installed to keep an eye on the power amp voltages and current draw. If everything checks out I will proceed with the normal start up procedures.

Matt J.

[Matt J]

I do have one concern going forward before I start installing the main board I would appreciate some feedback on.
Almost all of my previous D-Style builds have used the later used Mid switch seen on #102, #124, #182, etc. This is the first time I've wired up a Deep switch from the 2nd Gen and Classic era.
Since I'm using toggle switches instead of slider switches, I reversed the wiring from the commonly used schematic/layout of #40 but wanted to double check I did not miss anything so I can correct it now instead of later.
It's not my neatest work since I had to adjust a lot of stuff after some trial and error.
The pictures are hard to make out since you are cramped for space in that area and components block your view, so I quickly drew up how I wired it in Microsoft Paint.
Matt J.

[martin manning]

Flipping the slide switch layout it looks ok to me.

[jelle]

Yes, correct, have fun! jelle

[Matt J]

Thank you both!
The first Overdrive Special I built was many, many years ago and since it was a 70s circuit I've always suspected I miswired the deep switch and just never caught it. I never bonded with the PAB on that amp either and I've wondered if an issue with the deep switched affect that somehow. I'm very curious to see how it turns out with this amp.

Matt J.

[Matt J]

I ran another power up test last night with the power supply and everything came out in the clear.

Finished up some work on the main circuit board and started installing it. Much of the preamp is now wired in place. Now I'm mainly looking at the best ways to route some of the longer leads like the power amp grids from the PI to keep them away from noisy B+ sections.

The screen and grid resistors are elevated aways from the power tube sockets and connected to terminal strips so they're not right over the tube and subject to so much heat from the filaments. I know many layouts of Dumble amps and others have them connected to unused portions of the tube sockets, but I've gotten where I do things this way as a preventive measure against heat wear on the resistors. I'm trying to be as careful as possible about that and other points of stress since this is going into a combo cabinet.

Matt J.

[Raoul Duke]

Very neat and tidy build Matt!

[dbharris]

Looks great Matt! Did you run that V2a cathode wire like that intentionally rather than looped around next to the V2b plate?

-Dan

[Matt J]

Very neat and tidy build Matt!

Thank you!

[Matt J]

Looks great Matt! Did you run that V2a cathode wire like that intentionally rather than looped around next to the V2b plate?

-Dan

That was a bit of an accident, but it is something I may look at redoing later today.

[Matt J]

I caught an error in the wiring for V3 then finished wiring up the heaters last night.

Tried a quick smoke test with my current limiter to double check everything. No issues on start up and voltages looked good.

I'm going to double check some solder joints later today and look for any other error later today then I'll proceed with the rest of the start up.

Matt J.

[Matt J]

Went for a full power up test this evening.
No smoke, pops, or crackles.

It is not passing any signal along however, so I've been tracing that down.
I'm pretty certain it is something in the preamp. Tapping on some of the components in the phase inverter and power section will make sound. None of the front panel controls affect this any way.

Voltages are as follows:

5-6-2024 Voltage chart.png

Further, I am not getting the proper amount of negative bias voltage. Currently, with the plates at ~441VDC the lowest I can get is ~63mA.

Matt J.