new build choice, 2nd gen 50w

[erwin_ve]

Marcus, I would stick to your own diagram, because when the front panel manual is engaged the Od will be on because the relay will not be energized. In other words if you stick to #124 relay circuit including the wiring for the pedal you'll be ok.

[martin manning]

erm...so depending on which way would have an effect on the LED's? i.e one way would have the LEDS's on when in clean which would be backward..something that happened on one of my builds in fact.

Yes, exactly. The usual set-up is to ground the relay and LED together, so the LED is on when the relay is energized, and as I've drawn it, OD is on.

I'd use the panel switch to engage OD manually (grounding the relay coil), and the same with the front panel pull-switch to engage FET boost manually. Left "in," the boost is controlled by the footswitch, and LED on means Boost on.

You can still use the 4-ohm tap for the NFB, but the you will have to find a place to connect it, which could be directly to the feedback resistor on the board. I think I would run the FB from the output jack as usual, and increase the FB resistor by a factor of 1.41 to compensate for the higher voltage on the 8Ω vs. the 4Ω.

[erwin_ve]

Fwiw on my last 70-ies 2nd gen hybrid I wired the Od relay as described by Martin. But in every Dumble Ods the Od is on when the coil is not energized. Most detailed pics and layouts with #124 and#102 are availaible. Both Martin's way and the way in the layouts will work. I can't hear a difference.

[norburybrook]

Fwiw on my last 70-ies 2nd gen hybrid I wired the Od relay as described by Martin. But in every Dumble Ods the Od is on when the coil is not energized. Most detailed pics and layouts with #124 and#102 are availaible. Both Martin's way and the way in the layouts will work. I can't hear a difference.

As for the NFB tap: is the wire from the 4 Ohm tap available? you can directly solder that to the NFB resistor.

Yes I have a 4 ohm wire, I did think about that

I forgot to order an impedance selector, but realised as a combo it's not needed, so I've used the two output jacks fro 8 and 16 Ohm.

So I can solder the 4 ohm tap straight to the board?

M

[erwin_ve]

Fwiw on my last 70-ies 2nd gen hybrid I wired the Od relay as described by Martin. But in every Dumble Ods the Od is on when the coil is not energized. Most detailed pics and layouts with #124 and#102 are availaible. Both Martin's way and the way in the layouts will work. I can't hear a difference.

As for the NFB tap: is the wire from the 4 Ohm tap available? you can directly solder that to the NFB resistor.

So I can solder the 4 ohm tap straight to the board?

M

Yes but I'm not sure, because most OT wires a so thick I doubt it will fit in in a eyelet.

[martin manning]

But in every Dumble Ods the Od is on when the coil is not energized. Most detailed pics and layouts with #124 and#102 are available.

I don't think this is true. As far as I can tell Tony's layouts show OD on when the relay is energized, as does icracer's 124 schematic, which was was accurately drawn from the photos. In the 2nd Gen layout the panel switch is labeled "Manual" in the UP position, which grounds the relay and energizes the coil (however the ground connection of that black wire is not clear).

[erwin_ve]

But in every Dumble Ods the Od is on when the coil is not energized. Most detailed pics and layouts with #124 and#102 are available.

I don't think this is true. As far as I can tell Tony's layouts show OD on when the relay is energized, as does icracer's 124 schematic, which was was accurately drawn from the photos. In the 2nd Gen layout the panel switch is labeled "Manual" in the UP position, which grounds the relay and energizes the coil (however the ground connection of that black wire is not clear).

Martin, now I'm confused; why is the manual od relay relay on those #124 and #102 layout wired backwards?

[martin manning]

So you are seeing the same thing I am in all the layouts and schematics, i.e. OD on when the coils are energized?

[erwin_ve]

I think so, my mind is playing tricks on me. At work right now, multitasking isn't for accuracy I'll guess.. Sorry!

My brain was farting with the Ceriatone layouts, they did it backwards not Dumble.

[martin manning]

Yes! I was also recalling that they did it backwards and caused some confusion a few years ago.

[norburybrook]

well got all my wiring done, except for all the FET stuff. I suppose if I connect the B+ to the FET board and ground it I can fire up and test everything except the FET

Any idea where the manual/footswitch overdrive switch is grounded? and in which position is the half power switch in half(triode) and full (pentode)?

I presume that could throw me a curved ball with voltage checking.

As always thanks for everyone's help in getting me thus far.. I doubt the journey's over yet though...............

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any reason NOT to have flown the wires to the relay?

M

[martin manning]

Run all the relay and footswitch grounds back to the relay power supply ground. Where is that, you ask? Don’t know... Make one somewhere near the voltage doubler board.

I strongly suggest you bias the FET using the battery method first. You’ll be chasing your tail if you try to do that when it’s powered from the amp’s B+ rail. That shouldn’t stop you from testing the amp’s power supply, just don’t expect to get the right voltages on the FET.

Triode mode results when you disconnect the screen resistors from the screen node and connect them to the plate node. You should be able to work it out from there...

[norburybrook]

Can I use the regulator middle leg ground, I have the relay board grounded there? I've always wondered why there's an extra ground added for that when it grounds through the center hole of the TAG strip.

M

[martin manning]

The regulator tab is also a ground. Yes you can bring all the relay supply ground returns back to the regulator. You could daisy chain the FET boost switch manual ground wire to the OD manual/pedal switch and then to the regulator.

[pompeiisneaks]

Can I use the regulator middle leg ground, I have the relay board grounded there? I've always wondered why there's an extra ground added for that when it grounds through the center hole of the TAG strip.

M

My best guess is that the screw can slowly come loose over time and lose ground. The wire that's connected to a physical ground point that's screwed in by itself is usually more consistent, so you get a guaranteed ground just in case.

Similar to output jacks, I now started adding a ground connection to the chassis because the physical ground via the jack itself can, over time, come loose.

~Phil