Dumbleator Layout

[jazzbass]

I need a suggestion for the Hammond transformer, which transformer should I look for for the European wall voltage of 220V?

I don't know of any single transformer that has the specs you are after.

Another option would be to use two flat-pack transformers: https://www.hammfg.com/electronics/tran ... er/229.pdf These are quite small in size, and inexpensive.
I would use 229E12 for the heaters, and 229B230 for the plates. The 229B230 has 230VAC secondary voltage with 230VAC input at full load (50mA). The regulation is not very good on small transformers, so the voltage will be quite a bit higher at partial load.

I have a very similar Triad FP230-50 unit here, and I measure 258VAC on the secondary (series connected) at 110VAC input (primaries connected in parallel) with no load. That would result in 363 VDC using a full wave bridge, again with no load. You would of course connect the primaries in series for your 220VAC line voltage. You won't be using anywhere near 50mA, so the voltage will not sag much. If I add a 50k load resistor to the secondary, the voltage only drops to 254, and that would be 5.1mA, more than enough for the two triodes in the D'lator, and that produce just about 360VDC.

Hi Martin,

thanks for the suggestions, I have difficulty in finding these transformers available in Italy, one is available and the other is not.
At home I have a transformer bought years ago for this project which I then never realized, it is a toroidal transformer purchased from Tubetown, the tt-t47 with these characteristics:

P = 47 VA
Pri: 0-220 or 230 or 240 Volt
Sec: 250 Volt - 6.3 Volt - 12.6 Volt

It could go well? I'm worried about the voltage of 250 volts at the secondary .......

[martin manning]

That should work for you. 250 x 1.414 is 354 peak, which will be fine I think. Is your line voltage at 220? That is on the low side for EU isn't it?

[jazzbass]

Hi Martin,

thanks for the reply, the voltage at the wall socket is 226 volts.

Franco

[Richard1001]

I'm planning to make another dumbleator and while searching for information I was looking at the pictures and lay-out in this thread.

I wondered why the picture of the dumbleator shows an 18k tail resistor while the lay-out shows a 27k. Is this the value of another dumbleator?

And is the 250k Drive pot a measured value? It seems so strange to drive studio effect processors with a high resistance pot.

[erwin_ve]

Hi Richard, I've seen pictures here on TAG starring dumbelators with different cathode follower tails:
1k8-27k
1k5-15 or 18k
1k5-10k

[pfarrell]

Some recent discussion on the send buffer and cable loss (https://ampgarage.com/forum/viewtopic.php?f=4&t=32162) got me looking into the frequency response. It's true that the buffer is not very well equipped to handle long cables with its 250k send pot, and that will be a problem if the buffer's output is run out to a pedal board. Attached below is a tweaked schematic that addresses that, and includes an alternate power supply using a current production Hammond transformer that will fit in a 1u rack box.

The lower value send pot is accommodated by raising the cathode resistor and tweaking the bias point. If that is all you are after, you can just change the pot, Rk, and Rbias, and leave everything else alone.

Martin! I'm going to build a Dumblelator (why not?) based on this rev schematic you posted—since finding the original branded/speced PTs is seemingly quite the effort. The Hammond is readily available. If you have a moment maybe you could spot-check the layout I made for the power board (using current radial caps)? My understanding of your schematic shows only value changes for the main circuit board, layout is the same. Thanks! I'll still tweak the power board size since the mounting holes are probably a little tight.

(Still LOVE the #183, I'm really only beginning to understand what a gift is as my guitar skills sloooooowly improve—would have been A LOT more work without you and Ian.

Dumbleator_Update_MPM.png

Dlator_Rev_Layout_MPM.png

[martin manning]

Looks good to me. I'm not sure if anyone else has built one like this yet, but it should be fine, and better able to drive long cables.

[pfarrell]

Here's a slight adjustment to Martin's boards with measured components that I have, clearly Martin's build is insanely tidy, but parts I have here wouldn't have fit in a few places—including the small L-brackets I tend to use all the time. I also would prefer to mount the socket directly to the G10 as opposed to using standoffs, with a bigger hole and the pins out the back, like we do all the time with chassis mount—had to make clearance for the mounting rim of the socket. I don't have all the components in hand yet—so, not quite tested.

Dlator_Rev_Layout_MPM_r2.png