Dumblelator straight-up, with a twist

[dcribbs1412]

Hats off to you Martin
awesome looking build
thanks so much for the great layout

Darin

[SoundPerf]

Very nice build. In fact..perfect.

My orders to build a Dlator are shipping to me as I write this. One should arrive tomorrow. I ordered a 13.5"X5"X2" enclosure to put it in. I don't think it will be as tight as this, but I expect some challenges.

I went round and round on some of the choices of parts. In my case, keeping costs down while maintaining proper "mojo" was part of the consideration. From what I could make out, it looks like you went with 225P's on the poly caps? Same here.

Where I flaked a little was on the trafos. I was going to get the Tube Depot Button or the Allen, but wasn't sure about the voltages. I had figured out how to get the proper B+ but wasn't sure if the 100K RN65D on the plate of the recovery stage would be correct. So I went with two trafos. One with 140 VAC on the secondary and keeping the voltage doubler and a second 6.3VAC for the heaters.

I would've loved to see this post a few day ago.

I'm drawing plans now. I'm also concerned with noise issues. I think I can maintain good grounding scheme.

"edited to correct voltage"

[martin manning]

Hey, thanks Darin, and you're welcome.

SoundPerf, thanks; it's not nearly perfect... I know where all the flaws are, and I've hidden them well! Yes. 225P's, 400V except the 0.47 is 200V. I'm sure your two PT set-up will work fine, and from what I could tell the sound was very good running 30V low, so it's not too critical. You'd want to keep the 100k for the plate load even if your B+ is a bit higher or lower than spec; that stage wants to be center-biased and up in the linear part of the plate curves.

[David Root]

I've done Normster's buffered loop built in to the head amp twice, and it sounds good. I like it with a 12AT7 rather than a 12AX7.

Yes it's a truncated design compared with the Full Monty. Are there any of you have done it both ways and could comment as to tone/feel of both?

[SoundPerf]

You'd want to keep the 100k for the plate load even if your B+ is a bit higher or lower than spec; that stage wants to be center-biased and up in the linear part of the plate curves.

That's what I figured was the case. I kept checking everyones builds and they all kept that the same. I figure since the original went to the trouble to use such precision resistor there, it must be important. Thanks for the heads up.

[Structo]

Make sure the cathode voltage on the cathode follower is right around 30v for best performance.
You can adjust the 27K tail to adjust that if needed.
But if I recall, I adjusted the dropping string to achieve the voltages I wanted.

[SoundPerf]

Make sure the cathode voltage on the cathode follower is right around 30v for best performance.
You can adjust the 27K tail to adjust that if needed.
But if I recall, I adjusted the dropping string to achieve the voltages I wanted.

I've been using this Java based Analog Circuit Sim to do my calculations. Available here. http://www.falstad.com/mathphysics.html

It seems pretty accurate. Although with my 3.0Ghz dual core system, a Dlator size circuit starts to process pretty slowly.

Anyway, right now I'm showing ~28V on the cathode. If I raise the 27k to 30K I get 30V exactly. I have 259V on the plate of the input stage. It will be interesting to see what the real world results will be.

[Structo]

Sounds good!

Geez, I would think a 3 GHz Dual Core would run any sim pretty fast.

Of course you have to have at least 2GB of RAM if not 4.

[SoundPerf]

Sounds good!

Geez, I would think a 3 GHz Dual Core would run any sim pretty fast.

Of course you have to have at least 2GB of RAM if not 4.

I have 4GB. It runs Ok, it just takes a little bit for voltages to adjust after changes. I do have the full dlator circuit running though. I also have Win7 64bit. With 64bit Java. I think I've seen performance issues with older Java programs.

Thanks for the info, BTW.

[galtjunk]

I built a loop using the Allen transformer.
It fits inside a 1 space rack.
I built it using the power supply board in Martin Mannings drawing.
That drawing is in the second post in this thread.
I ordered 2 transformers to meet the $50 minimum.
Now that I have 2 amps I might as well have 2 loops.

Good luck.

[mrdarwin]

Hi!
I built a MP Manning dumbleator.
It works BUT there is a big hum, as loud as the signal of the preamp!

I respected all the grounding
All the voltages are good
Shielded signal wires
When I switch off the unit, it works perfectly during 15sec... because of the psu capacitors.

I tried to put the power xformer out of the case, same deal...

There is something I don't understand...

[martin manning]

Is the hum 60 Hz or 120 Hz (or 50 or 100 if you are in one of those zones) ? This will tell you whether the hum is from the AC heater circuit (center tap not grounded for example) or from the HV rectifier.

[mrdarwin]

Is the hum 60 Hz or 120 Hz (or 50 or 100 if you are in one of those zones) ? This will tell you whether the hum is from the AC heater circuit (center tap not grounded for example) or from the HV rectifier.

It is a 50hz hum circuit...
The toroidal has:
6.3v with no center tapped
12.6 with no center tapped

do I need a center tapped for heaters?

[martin manning]

Yes. Connect a 100-ohm resistor from each leg of the heater winding you are using to ground to create a virtual center tap.

[mrdarwin]

Yes. Connect a 100-ohm resistor from each leg of the heater winding you are using to ground to create a virtual center tap.

It works if I connect pin 9 to ground... but is it safe? do I have to add a 1ohm resistor between pin 9 and ground?

I'm gonna try your solution too!

Thanks for your help!!!!

will post some pics...