Supro S6424 project

[sluckey]

Recorded with a 50^th Anniversary Strat, S1 system engaged, bridge pickup, 6 month old strings, guitar wide open. Straight into amp at about 60% on volume, both channels. Galaxy S5 phone. Recording sounds a littly muddy to me, but it sounds brighter in the shop. I ain't got sharp ears. SG, you can jump in my corner anytime.

[shooter]

with all that hoopla stuff you used,  did you find you dialed a "sweet spot" on the tone knobs then forgot them, or were you tweaking and playing?  I stole the tone knob circuit from your build and find there is a narrow range 4-6 that just works well for me and I forget about it once it's dialed?  anyway just curious, thx

dave

[bnwitt]

Sounds great Steve.  Not bad for cell phone.  I'm sure the actual in room experience is something else indeed.
Barry

[tubenit]

THANKS for sharing the sound clip! Sounds good.

With respect, Tubenit

[sluckey]

Thanks guys. Shooter, my ears are not good enough to recognize sweet spots anymore. I don't even know how I had the tone set other than one channel was set a little bright and the other channel was set a little dark. Early on I did rotate the tone knobs through the entire range and noted that they went from muddy to way too bright. I set it somewhere in between and then just flipped the strat switch for a tone I liked. The amp is too loud for me when it reaches the distorted sound that you heard. Not too loud for a band, just too loud for me by myself. My dog thought so too. She would not stay in the shop! 

[shooter]

they went from muddy to way too bright.

Thanks Sir, that's what I found also, but somewhere in the middle just worked
And my ears are not far behind

[pompeiisneaks]

Someone's Jimmy Page is showing :)  Sounds great!

~Phil

[CraigB]

That's cool Steve!  I think I have everything I need to get started.  I think my chassis is 16x8x3, so I'll have plenty of room.  You mentioned that you'd like to see how the build goes and maybe others would, as well.  I'll just ask since this is your thread and you're a forum moderator here, would you like me to add to your thread or start a new one?  Thanks!

[sluckey]

This thread is already pretty long and will probably fade away soon. Probably be better to start a new thread. Looking forward to following.

[Ed_Chambley]

Sounds good Steve.  Phone worked good.

[sluckey]

I just realized that I never posted a link to my Supro webpage. It's mostly the same info found in this thread, but in a more condensed and organized manner.

     http://sluckeyamps.com/supro/supro.htm

[davidwpack]

Very nice work!

[adamG]

Steve,

Very nice job!
Thank you for this project, very much. I also follow this one.
My question is where might I put the effects loop?

My Supro build is with MV, as you instructed me. I will see ,if this works well.
Anyway, I'll give you feedback with success or fail;)

Thank you in advance.

Regards,

Adam

[sluckey]

My question is where might I put the effects loop?

That would have to go between the junction of the 270K channel mixing resistors and V2 pin 2. Whatever you do, be sure that V2 pin 2 has a resistance path to ground, maybe add a dedicated 1M grid leak resistor.

[adamG]

Thank you Steve, very much.

Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?
Those ones are two times cheaper then 6973. I mean JJ;)
My build is gonna be with 47uf on rectifying as the first cap. That's because, I do not like tube rectifiers. So, I can provide a bigger one.
Is your 22uf cap enough to reduce hum?

Regards,

Adam

[terminalgs]

great thread, great build!

Sorry, no sound clips. I don't have any recording equipment.

Ah, so just when you thought you've run out of amps to build, a new door opens.   maybe build a couple mic pre's?  maybe one with 48V phantom power to a condenser? a small mixing amp with an output to your phone.. later a computer..  later pro gear gates open...

I had a chance to try some Jensen speakers today... C12N ceramic and P12N alnico. Surprisingly, I prefer the P12N to all the speakers I've tried.

The C12N was Jensen's beast at the time, 27oz magnet with a 1.5" voice coil.   Used heavily by Leo.. The P12N that it replaced was a much smaller speaker in terms of power handling.


The Valco speaker of choice for the 2x6973's was the more economy minded C12R with a 10oz. magnet and 1" VC.  That speaker (or a similar speaker, ill-equipped for bass frequencies) in a cheap -- (ahem, ... "more economy minded"....) small, open back cabinet is part of the key to valco 24.  (by '67 the C12R was a ~5oz magnet really only useful for department store or classroom speakers mounted on the wall...)

[sluckey]

Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?

You could do that. I don't know what would happen to the sound. Might just sound like every other 18 watt amp. I wanted the amp to be as close to the real thing as I could get so I stuck with 6973s. They sound different from all my EL84 amps. AES has an 11% off storewide sale right now.

Why don't you like tube rectifiers?

[terminalgs]

Do you think ,it might be possible to mod this circuit with EL84 to keep the amp's sonic character?
Those ones are two times cheaper then 6973. I mean JJ;)
My build is gonna be with 47uf on rectifying as the first cap. That's because, I do not like tube rectifiers. So, I can provide a bigger one.
Is your 22uf cap enough to reduce hum?

I'm with Steve on the EL84's.  If you want EL84s, 47uf and SS diode rectifiers in the power supply, you want something that isn't this circuit.

[adamG]

Why don't you like tube rectifiers?

Because, it means another expense (tube+socket+space+labour), bigger transformer, filtering caps limitation.
Also, no sonic influence, IMO.

[adamG]

I don't know what would happen to the sound. Might just sound like every other 18 watt amp. I wanted the amp to be as close to the real thing as I could get so I stuck with 6973s. They sound different from all my EL84 amps. AES has an 11% off storewide sale right now.

Yes, you might be right for above. It sounds wise.
Anyway, I am pretty close with my build, so eventual success will draw further path...

Regards,

Adam

[sluckey]

Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.

[Joel]

great thread, great build!

Sorry, no sound clips. I don't have any recording equipment.

Ah, so just when you thought you've run out of amps to build, a new door opens.   maybe build a couple mic pre's?  maybe one with 48V phantom power to a condenser? a small mixing amp with an output to your phone.. later a computer..  later pro gear gates open...

I had a chance to try some Jensen speakers today... C12N ceramic and P12N alnico. Surprisingly, I prefer the P12N to all the speakers I've tried.

The C12N was Jensen's beast at the time, 27oz magnet with a 1.5" voice coil.   Used heavily by Leo.. The P12N that it replaced was a much smaller speaker in terms of power handling.


The Valco speaker of choice for the 2x6973's was the more economy minded C12R with a 10oz. magnet and 1" VC.  That speaker (or a similar speaker, ill-equipped for bass frequencies) in a cheap -- (ahem, ... "more economy minded"....) small, open back cabinet is part of the key to valco 24.  (by '67 the C12R was a ~5oz magnet really only useful for department store or classroom speakers mounted on the wall...)

This is why I'm thinking of going with the WGS G12Q.  It's got a 1" coil and light magnet.  So it should pair up nicely.

[adamG]

Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.

Steve,

Yesterday, I fired up my Supro with 6973 onboard.
Plate voltage is up to 350V (energetic network fluctuations at my place). On cathode I've got 25,2 V. Cathode resistor 360R. So, it means that output power is appox.22W.
Nevertheless above, I feel that the amp is too weak. This is my first built with that type of PI. Maybe, the power is not as big as in the long tail pair PI?
MV seems to work fine. I provided stereo 500kA pot as you suggested. The only difference is I applied two 2,2M resistors across both pots. Maybe ,I should change the MV pot(s) value?!

Thank you in advance.

Regards,

Adam

[sluckey]

I don't think mine is as loud as my Marshall 18 watt. But I don't consider it weak sounding either. This is my first experience with the paraphase inverter too. Could be a factor.

[adamG]

This is my first experience with the paraphase inverter too. Could be a factor.

So is mine;)
Today ,I just bypassed MV and that is the amp's final state.
This amp is not the powerful one. So, I also consider it as an experience.
If I am asked to build another one, I'll do it with poliester caps. My favourite polypropylene are too dark even to my taste.
Therefore, I suggest the other builders to provide those caps, IMO.

Thank you Steve, very much. 

Best regards,

Adam

[SoundmasterG]

Probably the only change you would need to make for EL84s would be the 250Ω cathode resistor. Just keep the B+ around 350V.

Steve,

Yesterday, I fired up my Supro with 6973 onboard.
Plate voltage is up to 350V (energetic network fluctuations at my place). On cathode I've got 25,2 V. Cathode resistor 360R. So, it means that output power is appox.22W.
Nevertheless above, I feel that the amp is too weak. This is my first built with that type of PI. Maybe, the power is not as big as in the long tail pair PI?
MV seems to work fine. I provided stereo 500kA pot as you suggested. The only difference is I applied two 2,2M resistors across both pots. Maybe ,I should change the MV pot(s) value?!

Thank you in advance.

Regards,

Adam

The paraphase inverter can actually supply more gain than the LTP or cathodyne. The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides. The LTP provides a distinctive tone that the other inverters don't and many people are used to that, so when a different inverter is used, they find they are missing that tonal thing that the LTP does.

The 6973 is based on the 6V6, though it comes in a 9 pin bottle and has higher voltage capability. The 6V6 isn't known for it's highs, so perhaps the 6973 is similar...I haven't tried that particular tube in a build yet so I don't know firsthand. Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.


Greg

[DummyLoad]

The 6973 is based on the 6V6

6973 is up-rated 6CZ5.

--pete

[adamG]

The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides...

Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.

Thank you Greg, very much. You knew, what I was asking for...
Yes, I am afraid that the amp is too dark as It should be as a Supro replica. I prefere Fendery tones. So, for me the amp is ok. But, it has been built for my friend, who expects that characteristic highs and grittiness.
Could you explain me what is floating paraphase and how to tweak the amp to be moore close to 6424 tone, please?

Thank you in advance.

Regards,

Adam

[SoundmasterG]

The 6973 is based on the 6V6

6973 is up-rated 6CZ5.

--pete

Yes it is directly, but it can be traced back to the 6V6. There was an article in Vacuum Tube Valley issue 15 about it and other 9 pin "dumpster" tubes.


Greg

[SoundmasterG]

The one that Supro used is rather unbalanced, and as a result the highs can be muted somewhat. (The amp can sound dark too if there is a lot of unbalance) The floating paraphase balances better and still gets some of the grittiness that the paraphase provides...

Anyway, I would bet with further tweaking you should be able to get the amp to give up the goods better.

Thank you Greg, very much. You knew, what I was asking for...
Yes, I am afraid that the amp is too dark as It should be as a Supro replica. I prefere Fendery tones. So, for me the amp is ok. But, it has been built for my friend, who expects that characteristic highs and grittiness.
Could you explain me what is floating paraphase and how to tweak the amp to be moore close to 6424 tone, please?

Thank you in advance.

Regards,

Adam

If you want the raw Supro tone you need to stay with the un-balanced paraphase as they used. You can adjust the value of the resistors in the circuit to get more or less balance out of the phase inverter, but if it balances too well then you lose some of the Supro character. That said, it might still sound good with the floating paraphase, or at least have some of what you are looking for. I haven't studied the 6424 circuit in detail and don't have time to do so right now. You will never get the Fenderey shimmer and cleanness out of a Supro derived circuit though without changing a lot of things. They do lots of things but they won't do that Fender sound.


Here is a link to the floating paraphase circuit on Merlin's site:
http://www.valvewizard.co.uk/paraphase.html


You can also study the Vox AC100 schematic as it used a floating paraphase with a 12AU7.

Greg

[adamG]

If you want the raw Supro tone you need to stay with the un-balanced paraphase as they used. You can adjust the value of the resistors in the circuit to get more or less balance out of the phase inverter, but if it balances too well then you lose some of the Supro character. That said, it might still sound good with the floating paraphase, or at least have some of what you are looking for. I haven't studied the 6424 circuit in detail and don't have time to do so right now. You will never get the Fenderey shimmer and cleanness out of a Supro derived circuit though without changing a lot of things. They do lots of things but they won't do that Fender sound.

Thank you for above, very much.
Actually, I seems in acc. what you've mentioned, I have well balanced circuit, because I feel I did not received raw Supro character basis its schematic. It is more Fendery then Supro now. Amp sounds smooth and warm like a hell;) Both channels stay cleaned up to 80-85% of their volume.
So, the issue is how to get highs and grittiness of Supro?!
Any suggestions?
I applied polypropylene caps, mainly. Maybe, that is the reason of smoothness and warmness?

Regards,

Adam

[sluckey]

Which PT and OT did you use? Post voltages for each power supply node and all tube pins.

[g-man]

Deleted

[sluckey]

1) Is the switch on the intensity pot (SW-2) needed? It seems like you could use the foot switch and intensity pot to control the trem, but do you get any ticking or thumping noises if not using SW-2?

A front panel switch (whether on the pot or a separate toggle switch) is not strictly needed but I think it's very useful. But if you will always have a footswitch plugged in, it becomes redundant. Removing the switch will not cause any ticking/thumping noises.

Is your question based on the fact that a 500K-L pot with push/pull switch is difficult or impossible to find? If so, I assure you that a 1M-A pot with push/pull switch is easy to find and works great. The 1M pot will actually give you a stronger tremolo too.

2) Instead of the input jack switch to choose channel 1 or 2 or both, would running the shielded cable and 2.2K resistor to V1 pin 2 and a jumper between pins 2 and 7 give the same variety? Just use the volume pots to control whether you use a single channel or both together?

That'll work just fine. Since I prefer to run both channels all the time I would probably do just as you say if I were going to build another for myself. I think most people would like the switch.

[g-man]

Deleted

[SoundmasterG]

Thank you for above, very much.
Actually, I seems in acc. what you've mentioned, I have well balanced circuit, because I feel I did not received raw Supro character basis its schematic. It is more Fendery then Supro now. Amp sounds smooth and warm like a hell;) Both channels stay cleaned up to 80-85% of their volume.
So, the issue is how to get highs and grittiness of Supro?!
Any suggestions?
I applied polypropylene caps, mainly. Maybe, that is the reason of smoothness and warmness?

Regards,

Adam

A lot of the Supro sound is the lack of negative feedback, and the unbalanced phase inverter. Some of it is the use of ceramic caps. Obviously the voltages would matter as those determine the power output of the amp (along with the impedance of the transformer in relation to the tubes), but also the headroom and gain of each stage in relation to each other. You can deviate from standard values for the dropping resistors and adjust the voltages of each stage in relation to each other. If you have a scope you can adjust so the power amp distorts first, followed by the phase inverter, then the next stage, etc., to the front of the amp. This is called gain scheduling and you can tailor the amp to distort the way you want by adjusting the operating voltage of each stage. This changes the headroom and gain level of each stage. To make it work best, each stage should have it's own filtering node and dropping resistor. Assuming you used appropriate transformers to duplicate the primary impedance and voltages of the original, then you are left with the balance of the phase inverter and the caps you are using. Considering the original resistors used likely had a 20% tolerance, then you can play with the resistors in the phase inverter circuit to purposely unbalance it and get some of the Supro grit. I forget right now which specific resistors in the phase inverter circuit should be adjusted, but it is really only two of them in relation to each other to get the balance or unbalance, one in each side of the inverter, though I suppose you could play with all them in that specific area of the circuit within 20% of their value now and see what you get. The ceramic caps also contribute to the grittiness of the Supros....they aren't as "perfect" of a cap in comparison to polypropylene but that isn't the point of these amps.


Greg

[adamG]

Which PT and OT did you use? Post voltages for each power supply node and all tube pins.

Steve,

Here are measured voltages:
V1 - input -
1-188V
6-104V
3-2,44V
8-1,12V

V2-PI-
1-138V
6-165V
3-1,12V
8-1,67V

V3 - tremolo - I didn't ground it for measurement, so...
1-284V
6-145-158V,

Power tubes both-
1-8 - 340V
9-352V
7-25,2V

Power supply 230V.
Nod 1-354V
Nod 2-341V
Nod 3 - not measured;)
Rectifier - Graetz bridge.
Filament - 6,6V AC

OT by myself - primary 7,5K, secondary 4,8,16.

Regards,

Adam

[sluckey]

Your voltages look about the same as mine. Maybe the amp is working correctly and doing all it's supposed to do? I don't consider this amp to have a bright sound, more of a woody tone to me. The Jensen P12N alnico I'm using is fairly bright. Does your amp sound anything like the sound clip on my website? That was made with a cell phone and with the volume turned up pretty loud. Much too loud to talk over.

[CraigB]

This is interesting.  FWIW, I find mine to have plenty of brightness, not piercing brightness, but certainly not muddy, even with the tone on lower settings.  I think the lower volume clean tone and natural compression, being very pedal friendly and killer trem are what make the circuit shine.  Channel 2 does have more of a woody midrange than Channel 1. Using mine with a 12" 8ohm Eminence George Allessandro speaker in an open back cab and an assortment of single coil and humbucker equipped guitars. 


Steve, I have tried to get a decent recording with an iPhone and it clips awful.  I even tried placing the phone in the other room with the door open and just sounds awful.  Did you use any special app or just the voice memo recorder?  Your recording sounds pretty good

[sluckey]

Steve, I have tried to get a decent recording with an iPhone and it clips awful.

You gotta move up to the Galaxy! 

Seriously, I just laid my S5 face down about two feet in front of the speaker and let it rip. The S5 records a MP4 video that's too big to post here even though the video was all black. I used a software program to extract the audio and save as a much smaller MP3 file. The original MP4 still on my phone sounds brighter than the MP3 posted on my website. But the grind is there on both.

I can't say about the audio quality from an IPhone, but the quality of pictures from my old Galaxy S5 is waaay above the pic quality of my wife's IPhone 6.

[CraigB]

Ah hah, the Samsung vs. iPhone debate continues  well, no debate here...I'm stuck with a 6S for another year and a half - no likey!

[pompeiisneaks]

I love my Android phone, mines the LG G6, and I gave up on apples back on version 3 or 4, they lock you in so tightly they never let go and you need to fight to get away from them :P

I'm definitely amazed at how well that sound came out on a phone, for sure.

~Phil

[EL34]

Someone is requesting Sluckey's Supro board as shown in Steve's PDF file

I can make them as an eyelet or turret board
You can use the price calculator link below to submit the info
http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php

I already have the drilling info for this board on file so there is no extra charge for not having a .dxf file

The board is 3.125 inches tall x 8.5 inches long
There are 56 terminal holes
Note that I don't drill wire holes or mounting holes, only the 56 terminal holes
Pick the board type and terminal type in the calculator

This is what it looks like with terminal holes only

[sluckey]

Only $22.19 for a black turret board. Shit! I ain't never gonna build another board. From now on you can do my boards Doug. 

[EL34]

Yes, well the first one would be way more expensive 

[sluckey]

I'll just take the second one. 

[CraigB]

Yeah, that is a great deal!  Thanks Doug!

[EL34]

The prices would vary by material type, color and terminal type
The calculator sends me the specs/info for the board you want made

[mresistor]

You do really nice work Steve and this amp endeavor is no exception. I will join others saying thank you for the documentation of this project, making it available to all, and for all the help you selflessly  give to any who enter here. 

[EL34]

I have the drilling file already set up for this board

If anyone wants one, fill out the calculator program first here
http://hoffmanamps.com/php/PartsList/BoardPriceCalculator.php

Pick yes that you have a cad file so there will not be an extra charge

Pick the material type, color and terminal type
The board is 8.5 inches long

Fill out a note that says
Sluckeys 6424 Supro and I will know to use the drilling file I have already created

If you have other parts you need, go to my shopping cart and add a note to your order to add this custom board after you have filled out the board price calculator form
If you do not need any other parts, just email me to order the board after you have submitting the board price calculation form

Look at the screen shot below to see how I filled out the calculator form