Dumbleator dimensions?

[Mark]

I have been looking at a few pictures of Dumbleators and attempting to work out the spacings for the pots and switches.

I don't have anything I'd regard as concrete yet, but I would like to know what other peoples findings were?

[erwin_ve]

Check these topics:

https://tubeamparchive.com/viewtopic.php?t=4084

https://tubeamparchive.com/viewtopic.php?t=3944

[Mark]

Thanks for the reply. I have been looking at that thread today.

The measures are good, but didn't appear to be dead on. I'm sure if Funk built it, it sounds simply wonderful, but I get somewhat anal retentive when looking at these pix. I will have to live with decisions I make at this point in time.

[glasman]

Thanks for the reply. I have been looking at that thread today.

The measures are good, but didn't appear to be dead on. I'm sure if Funk built it, it sounds simply wonderful, but I get somewhat anal retentive when looking at these pix. I will have to live with decisions I make at this point in time.

What are you attempting to build an exact replica of a dlator? If so you are going to have to find someone that owns one have have them measure things for you. Of course I doubt there were ever two dlators that were built exactly the same. He used chassis he found at local salvage store and probably did the screening himself.

If you are not building an exact copy the layout is pretty non-critical for the most part. When I designed the Matchbox I started out with the basic idea for a layout in my head and used Corel Draw and Autocad to finalize the mechanical plans and a PCB design program for the power supply and mainboard. Of course I did change a few things in the design, I don't like voltage doublers, use DC filaments and having my owning grounding methods that make them quieter.

There is more than enough information in these forums to build a functional external loop.

Just my 2 cents

[Mark]

Thanks for the reply, and your replies have made me think a bit about the design.

I'm now wondering what to expect from a completed D/L build.

What is it that you don't like about the voltage doubler?

A 12AX7 is operating in class A, so voltage sag isn't an issue. Without building the loop, it seems to me that as long the supply has sufficient regulation and is quiet. What is the problem?
(If I have missed something, please let me know.)

DC filaments is always a tricky decision, extra components usually means extra items that can fail. I know a lot of guys prefer raised filaments over DC filament. I haven't experimented with either so I can't comment.

Earthing, this surely must be one of the most misunderstood parts of building any amp project. What I'm curious about is the method you use for determining the best earthing layout?

While still on earthing, I was wondering if raising the ground potential over the earth potential was necessary to eliminate earth loops?

When building a stand alone reverb unit, I encountered the earth loop problem. I either had to remove the earth or raise ground above earth potential.

What are your thoughts on this one?

Thanks for your assistance.

[nickm57]

Hi Mark
Noticed you are in Australia.
I'm still trying to find a 1u transformer for my project.
From my understanding you can use a fender reverb transformer but it will not fit in a 1u rack case.There is a Euro toroidal but at 35 euro + shipping will end up a bit $$$.
Be nice to find a suitable transformer for 240 volts with out allot of playing around with the filament supply or similar problems.
I did read on another board Duane from Ledford might have ordered a run of suitable toroidals.
Nick

[glasman]

Thanks for the reply, and your replies have made me think a bit about the design.

I'm now wondering what to expect from a completed D/L build.

What is it that you don't like about the voltage doubler?

Voltage doublers in general have poor regulation when compared to a full wave or full wave bridge circuit. I think HAD used the trannies he did because this is what he could find.

A 12AX7 is operating in class A, so voltage sag isn't an issue. Without building the loop, it seems to me that as long the supply has sufficient regulation and is quiet. What is the problem?
(If I have missed something, please let me know.)

No you are correct there is not much strain on the power supply, I just think the full wave bridge for this application is a bit cleaner to implement and filter.

DC filaments is always a tricky decision, extra components usually means extra items that can fail. I know a lot of guys prefer raised filaments over DC filament. I haven't experimented with either so I can't comment.

The extra components for me a 1 Bridge rectifier, 1 diode, 1 7812 regulator and 2 caps. If you size the caps correctly they should last a lifetime.

Earthing, this surely must be one of the most misunderstood parts of building any amp project. What I'm curious about is the method you use for determining the best earthing layout?

I use isolated jacks on the rear panel. I group the return grounds by stage (ie CF, Recovery 1, Recovery 2). All signal grounds come to a single point. The safety ground is at a location close to the AC connector.

While still on earthing, I was wondering if raising the ground potential over the earth potential was necessary to eliminate earth loops?

When building a stand alone reverb unit, I encountered the earth loop problem. I either had to remove the earth or raise ground above earth potential.

What are your thoughts on this one?

I tried something similar in one of the early designs of the Matchbox. I did not find it made any improvements. Of course this was on a unit with isolated jacks and separate ground returns.

The best way to eliminate ground loops is to eliminate the ground paths. The only two ways I know of to accomplish this is to use optical coupling or transformer coupling. I am working with Jensen transformers to build a high quality transfomer to use in a studio version of the Matchbox and a rack guitar preamp for this very reason.

Gary

[glasman]

Hi Mark
Noticed you are in Australia.
I'm still trying to find a 1u transformer for my project.
From my understanding you can use a fender reverb transformer but it will not fit in a 1u rack case.There is a Euro toroidal but at 35 euro + shipping will end up a bit $$$.
Be nice to find a suitable transformer for 240 volts with out allot of playing around with the filament supply or similar problems.
I did read on another board Duane from Ledford might have ordered a run of suitable toroidals.
Nick

Heyboer would probably build them for you. The transformers they build for me (same physical size as the Dumble (stancor?) trannie have dual primary windings for 120/240 operation.

I have also used flatpack transformers from Hammond that work fine in a dlator, although there is a bit more hum. Here is a picture of my original prototype. I have since went to a rear mounted transformer to save space and reduce hum.

[Funkalicousgroove]

Hi Mark
Noticed you are in Australia.
I'm still trying to find a 1u transformer for my project.
From my understanding you can use a fender reverb transformer but it will not fit in a 1u rack case.There is a Euro toroidal but at 35 euro + shipping will end up a bit $$$.
Be nice to find a suitable transformer for 240 volts with out allot of playing around with the filament supply or similar problems.
I did read on another board Duane from Ledford might have ordered a run of suitable toroidals.
Nick

Heyboer would probably build them for you. The transformers they build for me (same physical size as the Dumble (stancor?) trannie have dual primary windings for 120/240 operation.

I have also used flatpack transformers from Hammond that work fine in a dlator, although there is a bit more hum. Here is a picture of my original prototype. I have since went to a rear mounted transformer to save space and reduce hum.

It's a Triad R-2C, they were intended for Tube Meters, an old off the shelf part from the triad magnetech catalog.

I have some with 230/240 taps and grain oriented steel for 50hz operation if you need one.

Brandon

[heisthl]

If you forgo the rack unit the Fender stand alone reverb transformer works great and is available in export voltages. The transfomer hum can be eliminated by making a "fence" out of your filter caps. This size unit is a plus if your not dealing with rack gear.

[Mark]

Thanks for all the replies.

I have been looking at the Dumbleator 2 dimensions as many guys who build a regular Dumbleator include a pot on the input to the recovery stage to pad down hot signals.

Anyway, I will post a drawing, but this is what I have so far, Don't take these measurements as Gospel as I haven't drawn them up at full size yet:

(1) 3 3/8" from the left edge of the front panel is the drive pot,

(2) The first brightness switch is 1 1/4" from the drive pot,

(3) The second bright switch (to be omitted on a regular dumbleator) is 7/8" from the first switch (this switch should be 1 1/4" from the recovery A pot.)

(4) The recovery A pot should be 3 3/8" from the drive pot,

(5) The recovery B pot is 1 1/2" from the recovery A pot,

(6) The recovery B brightness switch is 1 1/4" from the recovery B pot,

The switches are a difficult one to do, firstly, they are grouped fairly tightly, secondly there is the ground A/B switch which most people omit, I assume this is a cap from earth to either side of the mains, the modern in-line filters are small and would do a better job I imagine. I suppose a ground lift switch could be put in this position in case of earth loops?

These measurements are taken from the RIGHT edge of the front panel.

(1) 7/8" from the RIGHT edge of the front panel is the ground switch,

(2) The on/off switch is 5/8" from the ground switch,

(3) The standby switch is 5/8" from the on/off switch,

(4) The LED bezel is 5/8" from the standby switch.

I will draw them up later and post the drawing, but until then, let me know if you have a problem with these dimensions?

Thanks for all your help and interest in my thread. I appreciate all the assistance offered to me.