Another Supro 6424 build (at least, when I have all the parts)

[bmccowan]

That's nice Tolex. I like it. Where did you find it? I only see it from Canadian suppliers. I see /13 is using it.

[Bash]

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.

[Bash]

That's nice Tolex. I like it. Where did you find it? I only see it from Canadian suppliers. I see /13 is using it.

The manufacturer is Kayline. They list it as "Pewter Trout Slub Bronco".
Mojotone sells something called  "Blackened Tuna Tolex", which seems to be the exact same material.

In Europe TubeTown is one of the dealers. The color is new, so they do not have it yet. Should arrive in February.
That is a long time to wait, but at least gives me enough time to finish the amp and figure out which speaker is the best match.

[bmccowan]

Thanks - found Kayline - great selection. The Vintage Amethyst Bronco looks interesting too for a Valco build. They are in New Jersey but oddly the only dealers that list it are in Canada. I contacted Kayline. Mojo's Blackened Tuna does indeed look like the Trout stuff.

[Bash]

The Vintage Amethyst Bronco looks interesting too for a Valco build.

I found that one too, but it is a bit too purple for my taste.

[Bash]

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).

[Bash]

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 (I updated my layout file in the first post).
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. And  I always really loved the reissue.
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 amp (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?

[sluckey]

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?

First, you have a 270K resistor on the INT pot. That should be 2.2M.

You can replace the 1K resistor that's connected to V3-8 with a red LED (anode to the tube). This will greatly increase the tremolo oscillator output and "allow" a larger speed range. You'll likely need to increase the size of that onboard 1M resistor that connects to the FS jack to decrease the tremolo signal to prevent overdriving the preamp.

Now you can experiment with the speed. There are two things you can do. Increasing the value of any of the three feedback caps (.033, .022, .01) will slow the speed. I'd experiment with one cap at a time. I'd replace the onboard .033 with a .022 to increase the speed. Then use a SPST switch to connect the removed .033 in parallel with that new .022 to give you a slow speed range. This may be all you need to do. Here's an example. Look at page 2...  http://sluckeyamps.com/RCA/Ampeg_J12B.pdf

Another thing to try... Replace the 100K onboard resistor (the one that connects to the speed pot) with a 47K. This should increase the speed. Now replace that ground jumper on the speed pot with a 470K resistor to slow the speed. If you like this, then put a SPST switch across the 470K so you will have a Fast/Slow speed range.

30 minutes of experimenting should give you some joy.

[Bash]

Hi Slucky.

Thank you very much. I can't state sufficiently how grateful I am for your input and original work.
I will start experimenting (hopefully) this evening.

[Bash]

I experimented a bit.
First replaced the 270K resistor for the correct 2.2M one.
That mostly decreased the depth of the tremolo. So I changed it back, so the tremolo can become a bit choppy (almost on/off).

Also replaced he 100K resistor for a red LED. Did not need to change the other resistor. The preamp does not overload at all.

After a bit of experimenting I found that the best speed range for me was putting a 22nF paralle to the 10nF one.

[sluckey]

Also replaced he 100K resistor for a red LED. Did not need to change the other resistor. The preamp does not overload at all.

100K??? I hope that's a typo. The LED should replace the 1K resistor that's connected to V3 pin 8.

I did a bit of experimenting on mine too. I already had the red LED in mine so I'll use that as my baseline.

The baseline speed range is 3.46Hz to 6.24Hz. Not very wide.

Changed the .033 to .022. Speed range now 3.9Hz to 7.2Hz. Better fast speed.

Connected the .033 in parallel with the .022. Speed range now 2.84Hz to 5.16Hz. Much better slow speed.

Put the .033 on a switch to provide a slow and fast speed range. Now the total range is 2.84Hz to 7.2Hz. Very usable for me. This is how I left mine.

[PRR]

The LFO uses a 3-section network with one R variable 100k to 600k.

To a fair approximation the frequency will shift third-root of R or about 1.817.

Checks:
3.46Hz times 1.817 is 6.29 (measured 6.24Hz)
0.022... 3.9Hz times 1.817 is 7.1 (measured 7.2Hz)
0.055.... 2.84Hz times 1.817 is 5.16Hz (measured 5.16Hz)

IMHO the range "should be" over 2:1 so you can octave-transpose to meet your beat. But this is rarely done.

It is possible the SPEED pot could be 1Meg for 2.22X variation of rate. 22% more, a little, not a lot. But this is similar to Fender.

Changing _2_ of the Rs to pot-sections (a dual-gang pot) would give (for 500k+100k) more like X^(2/3) 3.3:1 ratio of speeds.

[Bash]

100K??? I hope that's a typo. The LED should replace the 1K resistor that's connected to V3 pin 8.

Yes, that was a typo. I replaced the correct one.

Changing _2_ of the Rs to pot-sections (a dual-gang pot) would give (for 500k+100k) more like X^(2/3) 3.3:1 ratio of speeds.

I am not entirely sure what you mean by this.

Do you suggest replacing the 100K + 500K potmeter by a dual gang pot?

[sluckey]

Do you suggest replacing the 100K + 500K potmeter by a dual gang pot?

Yes. One pot would be wired just as it it now. The second 500K pot plus 100K would replace the 1M.

Sunn used a triple ganged pot to change all three resistors in the feedback loop.

     http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

[Bash]

Yes. One pot would be wired just as it it now. The second 500K pot plus 100K would replace the 1M.

OK. Clear.
Now I wish the tremolo pots and the resistors and capacitors were a bit closer together in my layout 

Sunn used a triple ganged pot to change all three resistors in the feedback loop.

Good luck finding one of these...

Well, I don't have any dual-ganged pots around (or many other parts for that matter).
So I'll have to go shopping in the weekend before I can experiment a bit more.

[sluckey]

I tried PRR's suggested dual 500K pot. Also changed two caps. Speed goes from too slow to too fast. See pic...

[Bash]

That looks great, indeed.

Will try that this weekend.
Updated my layout accordingly.

BTW I really recommend reducing that 2.2M resistor that is connected to the intensity pot, for that "How soon is now" sound.
Used 270K myself.

[sluckey]

I'll give it a try while I have the amp on the bench.

[Bash]

Just performed all the changes.
Yes, it does work like a charm.

Nice range for both the intensity and the speed.

Thank you for all the help and tips.

[Bash]

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.

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.

Dual Tone track 1:
https://soundcloud.com/user-489882423/dualton-1?in=user-489882423/sets/dualtone-recordings
Supro track 1:
https://soundcloud.com/user-489882423/supro-1?in=user-489882423/sets/dualtone-recordings

Dual Tone track 2:
https://soundcloud.com/user-489882423/dualtone-2?in=user-489882423/sets/dualtone-recordings
Supro track 2:
https://soundcloud.com/user-489882423/supro-2?in=user-489882423/sets/dualtone-recordings

Dual Tone track 3:
https://soundcloud.com/user-489882423/dualtone-3?in=user-489882423/sets/dualtone-recordings
Supro track 3:
https://soundcloud.com/user-489882423/supro-3?in=user-489882423/sets/dualtone-recordings

[vampwizzard]

sounds great! especially the fuzzy tones.

[Bash]

sounds great! especially the fuzzy tones.

Thanks. That amp really likes old-school fuzzes and volume boosts.

[SILVERGUN]

Thanks for all of those samples.
That tremolo on the Dual Tone Track 3 is strong. Pretty close to the 'How Soon is Now' effect. (I like the Supro version also)

[Bash]

Thanks for all of those samples.
That tremolo on the Dual Tone Track 3 is strong. Pretty close to the 'How Soon is Now' effect. (I like the Supro version also)

That is what happens when you make the mistake to use a 270K instead of a 2.2M resistor.
For now I like it.
It can sound closer to the Supro, by either turning the intensity down a bit, or mixing in channel two.

[Bash]

Damn, getting that Tolex took ages.

So finally I have the cabinet done.
Really pleased with the result.


In the end, I settled on using a Celestion A-type in it, which sounds really nice.
Also tried the Jensen P12Q in it, but that was really overly bright for my taste.

[TIMBO]

AWESOME!!!!

[Bash]

AWESOME!!!!

Thanks.

And they sound really great together. They really complement each other.

[dbishopbliss]

Coincidentally, I just recovered my Silvertone 1482 in Blackened Tuna so it will have a similar look to your amp with the vertical chassis. I'm working on covering the baffle later tonight. I also just built a 1x12 (really big) for my VOX AC15 and I'm working on the head cabinet that will also be covered in tuna.


My question is, where did you get your face plates made? They look really sharp!

[Bash]

I had them made in Germany at tube-town.de
Since I live in the Netherlands, that was the best solution.

I am now going to use the same Tolex for covering a speaker cab with a Yamaha Ja1701a inside (the rotating speaker unit from old Yamaha organs and Ra-200 amps).

[Bash]

I decided to add a permanent power soak on the second output of the amp.
That way I can turn up the volume more, without going completely deaf, and the volume of the internal speaker (when I connect it to the second output) is in better balance with the volume of the rotating speaker (which is less efficient than the Celestion A-type).

I used a TRS input to make sure that the 8 Ohm resistor is not messing thing up when there is no plug in the second output.

I used two pairs of 20 Watt resistors in parallel to be sure they could handle the power (even though the amp is just 18 Watt).

[Bash]

And finally I had the time (and all the parts) to finish the matching cabinet, for the Yamaha rotary speaker (salvaged from an old organ).

I am rather pleased with the results.

[Bash]

And the final results.

[Willabe]

Very nice!!! 

[Bash]

Thanks.

I added an additional layer of speaker cloth on the inside (that flimsy black Hifi type of stuff) so the speaker is less see-through.

Also finished the foot switch with three options:
-On / off
-Slow / Fast (speed set by the knob on the back)
-Momentary switch that always ramps up to maximum speed, no matter how the other switches are set.

Here you can see it on top of the DualTone (the other foot switch is for its tremolo and tap-tempo for my delay pedals).