[Bas Hermus]

Hi everyone,

After I really enjoyed building my AC18, I was looking for a new project (stuff to do during the Christmas holidays).
I really like the Supro DualTone, so I looked around for a good schematic. I found one on Steve Luckey's website.

Using illustrator I have tried to translate it to TubeTown's 18 Watt format, using the same power transformer and output transformer.

In the drawing I added the option of switching the two preamps from parallel to series in order to get more gain (don't know whether this is a good idea).

What do you guys think?

[Bas Hermus]

I just noticed that I made a mistake in the layout. I connected the OT to pin 6 instead of pin 9 on all three 12AX7's.
Serves me for looking at the schematic upside down...

This is the corrected one.

[bluesfreak]

Hi,

that looks quite good, just 2 small things I would change:

1. 6973 has Grid #1 connected to Pin 3 and 6, I would bridge these pins to avoid having one side "floating"
2. same for Grid #2 , 6973 has Grid #2 connected to Pin 1 and 8, I would bridge these pins to avoid having one side "floating"

just my 2c

blues

[Bas Hermus]

Hi Bluesfreak,

Thank you for the tips.
I actually see this in his schematic as well.
However, I don't see it in his layout or photographs.

I will take these along.
I will also try to ask Sluckey why he did not do this.

[Bas Hermus]

Just got more information about this.

The pins are connected inside the tube.
You should not add these external jumpers (really not).

I attached the corrected layout again.

[Bas Hermus]

BTW it won't damage anything in the amp when you connect these pins, it just doesn't do anything.

[Bas Hermus]

BTW I updated the layout slightly.

I connected consistently to pin 1 of the power tubes (not 1 and 8 mixed).
That way you can also run 6CZ5 tubes instead of 6973 tubes.

NOS 6973's are outrageously expensive. NOS 6CZ5's not so much.

[bluesfreak]

Why running NOS when there is an actual 6973 doing a decent good job available?
https://www.tube-town.net/ttstore/eh-6973.html

[Bas Hermus]

Why running NOS when there is an actual 6973 doing a decent good job available?
https://www.tube-town.net/ttstore/eh-6973.html

I know. I have a couple of them already.
But with that small consideration while building you can also try the 6CZ5 if you want, without any modification at all.

Good news.
The parts arrived, so I can start building 

[Bas Hermus]

...and I found another mistake (when building the amp).

The 270K resistor was connected to the wrong potentionmeter lug for volume 2.
Fixed in the new pdf.

[Bas Hermus]

Just found another mistake (more like an omission).
I forgot two wires at the reverse side of the board, so I updated the PDF.

During soldering I was wondering why two capacitors would lead to a dead end.

Also found a really nice Tolex (not in stock yet at TT), that will creat a nice match with my Fawn AC18.


BTW
Does anybody have a good suggestion for a matching speaker?
I can't decide yet between a Jensen P12Q or a WGS C12c/s.

[Bas Hermus]

Finally had the time to progress a bit.

The board has been populated and all the wires attached to it.
It is mounted inside the chassis, but I still not to connect all the wires from it.

Again, found a few mistakes (resistor values), so I have updated the pdf.
Also reduced the number of ground wires that are needed, by adding a few shorts on the board.
Updated the colors of the wires to match the actual colors that I used (not useful for anybody but me).

[Bas Hermus]

Finally finished the amp.
In the end I removed the series/parallel option.
The amp really did not sound nice in series and it made some of the wiring needlessly complex.
So now the amp has two inputs:
-Input one is both preamps
-Input two is only the tremolo preamp

My first impressions.

I tried it out using two speakers:
-A Supro DT12, which came in my reissue Supro DualTone
-A Celestion Alnico Gold, which is installed in the AC18 shown in the first post


I really had the chance to compare it to the reissue Supro DualTone, and in my home-build one sounds better.
The reissue has more bottom end, but can be bass heavy. The difference is not that big.
The biggest difference is in the highs. The home-build one has plenty of highs, but does not sound shrill. The reissue can become a lot more piercing in the high end. Certainly at higher volumes.
As a results the home-build DualTone sounds a lot better using fuzz pedals. It really sings in a nice and creamy way that the reissue simply doesn't do.
I don't think that difference can be completely attributed to the difference in tubes. The reissue has all EHX tubes, my home-build one has JJ's for the preamp and rectifier and RCA 6CZ5's for the power tubes (I also tried it with EHX 6973, but that did not really make a big difference).

That was when using the speaker from the reissue DualTone.

When switching over to the Alnico Gold the first thing you notice is volume. Damn, that speaker is loud. A lot louder than the DT12. More bass as well.
It doesn't sound bad at all, but for me the Alnico Gold is not the right speaker for the DualTone. It simply doesn't fit very well.
To me it sounds as if it is trying to make the DualTone like a Vox amp, which feels a bit like Mel Gibson trying to sound Scottish.

Hopefully I have some time to record the map (will post clips).

Overall I am really pleased with the amp so far.
The reissue will be leaving soon, I guess.


One question
The range of the tremolo speed is very limited. It goes from rather fast to fast. No slow or very fast options.
Any idea how to enlarge the range?

[Bas Hermus]

Made some last changes, with help and input from the el34world forum.
Replaced the intensity pot for a dual one and changed a few resistor and capacitors.

Now the intensity and speed of the tremolo have a nice range of speed and depth.

I updated the layout with my changes.

[Bas Hermus]

Made a few quick recordings of the amps.
The ones labelled DualTone are from  my own-built amp.
The ones labelled Supro are from my reissue Supro DualTone.

https://soundcloud.com/user-489882423/sets/dualtone-recordings

Played everything on a Telecaster with a maple neck and Lindy Fralin pickups.
All tracks with a little bit of delay from a delay pedal. At the end of the first track I switched the boost part on of a JDM Tonemaster (=Germanium boost).
With the second track I use a homebuilt Solasound One Knob Fuzz copy.
The last track is just comparing the tremolos of both amps.

For all recordings I used a TwoNotes Torpedo Captor X with the exact same setting for the speaker emulation. That way I was sure I was really comparing the two amps and not possible differences in microphone placement.

I chose not to use a looper pedal for the recordings, but simply play everything twice.
In the past I have used a looper to that, but I noticed that I changed my playing slightly, based on how the amps reacted.