Dumbleator II build.

[rccolgan]

Couldn't sleep last night so I pulled together the signal boards. I'll work on the power supply next. My guess is the crossing wires for paralleling the tubes are done under the PCB socket based on the original being a single-layer circuit board.

[Charlie Wilson]

1uf is correct.
Cw

[Stephen1966]

Couldn't sleep last night so I pulled together the signal boards. I'll work on the power supply next. My guess is the crossing wires for paralleling the tubes are done under the PCB socket based on the original being a single-layer circuit board.

You're really going for it. Good on yer! Keep us posted

[rccolgan]

1uf is correct.
Cw

Perfect!! I should have guessed NTE! Thank you!!

Couldn't sleep last night so I pulled together the signal boards. I'll work on the power supply next. My guess is the crossing wires for paralleling the tubes are done under the PCB socket based on the original being a single-layer circuit board.

You're really going for it. Good on yer! Keep us posted

Ha! That's how I like to do it

[rccolgan]

I think this is about all I have left to give for today. I need to clean up some things but coming together quickly. I'm just using the "Dumbleator II" name as a placeholder. Once I'm happy with the individual boards, I'll put them together via "mouse bites" so it's cheaper to produce the boards (I think). I printed out 1:1 the layout and did a test fit in a Hammond 1U chassis and it fits snug between the top and bottom of the chassis so no rattling around.

Maybe I'll get around to the power supply tomorrow. I plan on trying two versions of the power supply.
* 1:1 original style
* Using Hammond 229 series transformers & 12v heaters. (You'll notice I separated out the heaters so the board can be universal for whatever the desired power supply is for the builder.

time for bed!

[rccolgan]

Question for the group. Do we know what the expected voltages are at the tubes? I admit I'm new to D'lators so I'm learning a ton. I know I can get fully rectified B+ ~320VDC @ 50ma by using a https://www.hammfg.com/part/229B230. I still plan on making a 1:1 original-style supply board, I personally am not too crazy about cutting out the hole for the transformer at the back and I'm trying to understand if transients in this Dumbleator circuit exist as they do in a full tube amp where the supply makes a difference in the bounce, compression, bass, stiffness, etc.

Please school me on the topic! I'll bring popcorn for the class...

Edit: I'm searching around and I see a few Dumbleator builds using 230v secondaries. I also see another schematic of a Dumbleator with a B+ of 365 (which is higher than I think can be achieved)

Double edit: just saw this thread recently :facepalm:
https://ampgarage.com/forum/viewtopic.php?f=4&t=36196

[Stephen1966]

I can't speak to the DII but using a 12AX7 in my "regular", single tube Dumbleator circuits I aim for the voltages Martin and prior to him, Tony detailed: B+1 = 360V, B+2 = 260V. A 100k resistor get you there with the 12AX7, then B+1 is dropped by another 100k resistor to the plate of the recovery triode and that puts you in the region of 230V on the plate. The aim is to get 30V on the cathode of the CF driver. That puts your bias point on the CF in a mostly linear part of the load lines. https://ampgarage.com/forum/viewtopic.p ... 05#p444405

Here's a thread on Dumbleator voltages: https://ampgarage.com/forum/viewtopic.php?t=31667

Edit: if you are concerned about transients in the PS, you might try ultra-fast switching rectifier diodes in the bridge UF4007s. You will get a slightly higher voltage drop (not enough to make any significant difference) but I'm using them in my 183 rectifier circuit and there are no issues.

[jazzbass]

The transformer or transformers are my biggest problem. For the first one I solved by buying a toroidal transformer from Tubetown for the first build (TT-T47) , too big for this application, but it worked.

maybe Piemme elektra - IT?

Hi Bepone,

do you have experience/opinions on the quality of these transformers? I have to find an OT for a Hiwatt DR 504 and I'm considering whether to take the one offered by Tubetown built by Savino Luce.

Thanks, a hug

Franco

[bepone]

Hi Bepone,
do you have experience/opinions on the quality of these transformers? I have to find an OT for a Hiwatt DR 504 and I'm considering whether to take the one offered by Tubetown built by Savino Luce.

Thanks, a hug

Franco

i bought several times laminations from Pieme and they have good quality lamination. Also they have cheap output transformers, so if is M6 lam. then is all ok. I bought 5E3 output but still didn't finished Tweedle dee project, will be soon

[rccolgan]

A few updated progress pics of the Dumbleator II board. I added the Mesa parallel mix circuit with a switch to fully remove the pot. I think I'm settling on calling this the Dominator III

Power supply is moving along and is very inspired by the London Power PSU-PRE-24 https://londonpower.com/electronics/tub ... er-supply/ which seems overbuilt (in a good way). Their power supply covers a lot of scenarios so I'm stripping the functionality down to just what we need for the Dumblelator and I'd like to take a crack at making a Phoenix preamp afterward. -12VDC heaters and +320+VDC B+. Hopefully B+ is higher with less load and I'll find out once I actually build one in the coming weeks.

[rccolgan]

Playing Tetris this morning. It's nice the C-3x is available

[dbharris]

Looking good! Tight squeeze in these 1u racks.

You probably already considered this, but double check any standoff mounting points that are in the vented area of the chassis for alignment with the existing holes. Mine were just a little off and I had to widen one of the vent holes to make it work.

Not sure how thick of a pcb board you will use, but on a long one like that (main board), I might add another L bracket to the middle for more rigidity when changing tubes.

-Dan

[rccolgan]

Thanks, Dan! It's ok to assume I didn't consider something so I appreciate any call-outs. I'm going to use 2mm PCBs and the long signal board is cut into two separate boards like the original Dumbleator II. One mount on each end of the boards (4x total between the two).

You might have noticed I'm using a slightly shallow-er chassis as well. If I can make this size work, it'd be a breeze for the longer styles. I'm hopeful that this size could fit on top of a ODS style head if that is a desired use case like the Two Rock Eli1.

Great tip on using the holes that are already cutout. I should probably be able to find the mechanical drawing for this Hammond chassis...

[rccolgan]

Alright I'm going to give this power supply a try. 120vac @100ma secondaries via 229b120. Martin's recommendation for a single tube supply is 125vac @ 15ma secondaries (Hammond 262a12) which boosts the voltage up to around 365vdc B+. I'm hopeful I can get close enough to that with the 120vac secondaries. There is enough current available for a few tubes and maybe a reverb transformer for future projects if this works out...

Any opinions & thoughts? See attached for the schematic and layout.

120v/240v mains outlet-friendly design too by leveraging the jumpers under the circuit board

[rccolgan]

I was able to shrink the signal boards and modify the boards so the vent holes line up perfectly with the mounts. Attached is a Hammond RM1U1908VBK rack.

Next up is a PCB manufacturing order