Supro 1624T Dual Tone

[Joel]

Hi All!

Has anyone built one of these?  I've attached the Schematic I found on this site.  I would really like to build this as my next amp.  I haven't found many forum threads related to building this circuit.

I'm particularly interested in what iron people have used.  Most of the transformer manufacturers have clones of the more well known classic amps, but nothing specifically for this one that I can find.  Hammond transformers are the easiest to get here in Australia so I'm looking at their iron.  Looking at their offerings, the Marshall 18W iron looks like the closest match for the 1624T circuit. 

I'm also wondering which WGS speaker would pair well with this circuit.  The re-issue amps come with Supro badged "DT12" 8 ohm speaker.

Opinions, thoughts, and inklings welcome.

[TIMBO]

Hey Joel, Welcome aboard.
I would think the 6973 is close to an EL84, so an 18w transformer set would work fine or Vox AC15

Try here. http://www.evatco.com.au/

[tubenit]

As an FYI,  it looks like Electro-Harmonix is making the 6973 and that they sell for around $20 each.

With respect, Tubenit

[kagliostro]

I think that 250K at the cathode of the 6973 tubes is a typo

may be they mean 250R (?)



---

With my pour knowledge ... to me seems strange that the resistors connecting the grid (G1) of the power tube to ground aren't of the same value

one is 270K + 12K, the other is 470K, is that a Paraphase PI ?


Franco

[DummyLoad]

6973 is mildly a hopped up 6CZ5 - mainly just voltage ratings. late production RCA 6CZ5 and 6973 are same tube. have not built one. looks like a fun build to put to an eyelet board or turret board.


--pete

[kagliostro]

Joel

May be you can have interest on this



seems that there was a tremolo issue

The solution for the tremolo issue





Channel 1: https://youtu.be/AceX1MlJgso

Channel 2: https://youtu.be/GqD6d6BQEdg

Source is here

http://music-electronics-forum.com/t43972/

Franco

[MacGwyn]

Watts tube audio has a nice kit of this amp available online including repro transformers and a beautiful chassis.

[tubenit]

I drew these up some yrs ago and simply put them in a file.  I think (?) they are supposed to be close to the original design but with 6V6's?

Anyhow,  maybe something here will be useful to you as these are editable schematics and layouts.

CHECK for ERRORS!  Compare the schematic I've drawn with the original and then check the schematic with the layout.  I don't remember if I ever checked these for accuracy after drawing them.

With respect, Tubenit

[DummyLoad]

one is 270K + 12K, the other is 470K, is that a Paraphase PI ?

yes, it's a paraphase. a good part of the mojo of the amp.

--pete

[jjasilli]

https://www.youtube.com/watch?v=gw1IJqSInNw
I'm in love

[DummyLoad]

http://www.youtube.com/watch?v=gw1IJqSInNw
I'm in love

really good tone coming out that little box.


--pete

[tubeswell]

I think that 250K at the cathode of the 6973 tubes is a typo

may be they mean 250R (?)

Yup I'd say so.

With my poor knowledge ... to me seems strange that the resistors connecting the grid (G1) of the power tube to ground aren't of the same valueone is 270K + 12K, the other is 470K, is that a Paraphase PI ?

The 270k/12k divider feeds the grid of the 2nd inverting stage in the paraphase, and doubles as the grid leak path for the output tube grid that is being fed by the 1st inverting stage. All the imbalances are 'designed' to provide some sort of counterbalance to otherwise pretty uneven gain structure that you would get it you had two inverting stages cascading into each other whilst taking one side of each output stage from each driver stage.

The thunderbolt PI is a pretty decently designed paraphase inverter. I managed to incorporate workable NFB loop into a couple of my amps using the t-bolt inverter.

[Joel]

Thanks for the input everyone.

All those layouts and schematics have been downloaded for future reference.

[sluckey]

I'm in love

I liked the video that jjasilli posted so much that I decided to build one more amp. I chose the Supro S-6424 because it is identical to the 1624 except that it really has two tone controls. Don't know why the 1624 is being called a "Dual Tone" when the original only had one tone control? Anyhow, good sounding demo.

I dropped the four input jacks on the original S-6424 and used a single jack and selector switch for either channel or both (jumped/linked). This project is underway. I'll start a new thread when I have more to show. Meanwhile, Here's my Visio layout plan...

     http://sluckeyamps.com/supro/supro.pdf

[jjasilli]

 

[kagliostro]

 

[terminalgs]

I have an OT from the 58/59 Rhythm King which was the 1622B, or non-trem version of the 1622T. Similar to what became the 6424. I reverse engineered the winding and found it to be 7.5K:2ohm (2 4ohm 6x11" in parallel).   Valco replaced the 2 oval speakers with a single 8ohm 12".   Classic-Tone still makes that 7.5K:8ohm as well as the Classic-Tone 40-18062: a 305-0-305 (6.3@1.75,5@2) replacement for valco PTs #3693, which was the PT used in many of those 2x6973s including the 6424.

[Joel]

Haha!  I've started something! 

I must admit I've been leaning towards the S6424 for the same reasons you did sluckey.  And now I'll have the privilege of seeing your work before I attempt my own.

One thing I have discovered, the re-issue Supro Dual Tone is a different amp than the classic.  The re-issue has a solid state rectifier, and 4 x 12AX7's.  Personally, I'll go with the classic design (but I'm totally stealing your input selector).

What speaker are you thinking of teaming up with it?  I've been thinking of the WGS G12Q.

Greatly looking forward to your build thread.

[terminalgs]

I'm also wondering which WGS speaker would pair well with this circuit.  The re-issue amps come with Supro badged "DT12" 8 ohm speaker.

Originally Valco used a C12R.  Which was maybe 15W?  If you believe in tone-cap mojo, your wallet is gonna like valco's affinity for ceramic disc Z5U's.

[clyde]

I built one last winter in a Harmony chassis turned around so the controls were facing frontwards.  With the cabinet mods I used two Weber Signature 10's.  The circuit was mostly faithful 1624 but the preamp was modded a bit to accommodate the Harmony control layout.  Outputs were 6V6 into a MM early tweed Super OPT.  PT was 275-0 Hammond with 5AR4 rectifier.  Quite a nice sounding project.