Dumblelator straight-up, with a twist

[martin manning]

Grounding pin 9 provides the needed ground reference and it is safe, but you should get lower noise if you use two 100-ohm resistors and center the heater circuit's AC at ground potential.

[mrdarwin]

Grounding pin 9 provides the needed ground reference and it is safe, but you should get lower noise if you use two 100-ohm resistors and center the heater circuit's AC at ground potential.

Ok, I will do this... but with 47r 1w because don't have 100r now

Thanks again!!!

[martin manning]

You're welcome. 150 ohms is another commonly used value in this application.

[mrdarwin]

here it is!

[mrdarwin]

and here...

[martin manning]

Nice work! What power transformer (manufacturer and model number) did you use? People are always looking for a low-profile PT for D'lators.

[mrdarwin]

Nice work! What power transformer (manufacturer and model number) did you use? People are always looking for a low-profile PT for D'lators.

http://www.tube-town.net/ttstore/Transf ... anguage=en

needs a virtual center tap!!!

[martin manning]

Looks like a good option for Euro-zone and UK builders.

[Structo]

The first Dumbleator I built had horrendous hum.

It was a ground loop that made the hum and I snipped one of the shielded cable grounds and it went silent.

Sorry I don't remember which shield I snipped but if you study the schematic you will see the proper way to ground and wire the shielded cable.

[pfarrell]

Old thread reboot—Is it better to have all the MManning content in one place? (now that the damage is done ). This project started in the files area... but it seems to me it should continue here? Martin, LMK.

Here's some chassis parts ready for tapping and finishing etc. I'll probably make the sides wood for some comfort. Roughing out a layout (will swap LED and PWR switch). I'll make a proper labeled front panel, maybe do the label-maker thing for the back....

Martin—artificial CT for the heaters? Also, on your schematic you note the first ground point in the PS as "isolated"...I'm assuming that you just want to see that as it's own separate ground connection, not actually isolated from the chassis?

Manning-Dlator_PF_01.jpg

[martin manning]

G1 is off by itself, away from the signal grounds. See in the layout drawing in his thread. I see I've swapped he numbering, though. The reservoir ground is labeled G2 in the old layout.

Since the heaters are running in series on 12V, the trick is to ground the tube's heater center tap, pin 9, which provides the heater ground reference.