Supro S6424 project

[sluckey]

I saw your Pathfinder conversion. Looks good. And I love the name. Now you need a "99" to complete the set!

[sluckey]

Got it completed today! The layout works and is very quiet. The amp sounds good and the tremolo is very good. The power tubes were idling at 25 watts with the stock 250Ω cathode resistor. I've replaced that with a 470Ω to cool it off a bit at 17.8 watts. That's about all I expect to change other than tidying up the wiring a bit. Tomorrow I'll update the schematic with my final voltage readings. Stay tuned...

[John]

other than tidying up the wiring a bit.

Yeah, good Lord it's a real mess.


 

[DummyLoad]

very, very nice! 


--pete

[Tony Bones]

Not sure about the knobs, but I love the rest!

[sluckey]

Gotta raise some money for a full set of knobs. Or steal from another amp! 

[kagliostro]

You can cut a broomstick for that purpose 

----

As always very nice realisation Steve 

Franco

[tubenit]

Fantastic job!  Well done, Steve.

With respect, Tubenit

[Ed_Chambley]

I hope all that summer sweat is worth it to play that mystical Jimmy Page stuff.  Nice job, but buy you some chicken head knobs and quit    about not having money for them.  Now you gotta build a Dragon Telecaster.


Nice job!

[shooter]

Not sure about the knobs

I have the same set!  As an abstract artist, messing with ppl's head is fair game 

[Ed_Chambley]

Not sure about the knobs

I have the same set!  As an abstract artist, messing with ppl's head is fair game 

Are you sure that is not INSANE artist?

[shooter]

INSANE artist

some famous human once said, there is a fine line 'tween..............I keep going back n forth seeing which side I like better   SSA just sent me my "projections" for retirement, I get more if I stay on the insane side

[sluckey]

We should get together Shooter. I bet we could come up with a full set of knobs between us. If not, surely we could get a very interesting mix!   

K's broom handle idea seems appealing.

[SILVERGUN]

I bought up stock on all those big, round, silver, knurled edge, Radio Shack knobs when stores were closing around here. I probably have 30-40 of them just sitting here. I see they are sold out online.
I'll gladly ship you a few if you want to PM me your address. (if that's the look you're going for)
https://www.radioshack.com/products/radioshack-silver-tone-knurled-knob
 
You can even save a couple for your next "last" amp 

[shooter]

We should get together Shooter

I have enough black n chrome to make you a full set, the RS diamonds also
next time I head south i'll load them with some MI craft beer n some home-grown n PM you

[sluckey]

I've updated the schematic with a couple notes and all my measured voltages. Stole some knobs. Now to straighten out that wiring. Maybe by the end of the week I'll be playing Whole Lotta Love! 

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

[Joel]

Thanks Steve for the awesome photo's and resources.

Can someone please check my math?  I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph.  In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k).  Plate max dissipation is 12W, B+ 350V. 

So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A).  Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point.   100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor.  This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result).  Yes?

This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve.  And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve. 

Am I understanding this correctly?  Have I drawn the load lines correctly?  I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?

[tubeswell]

Very tidy.


Soundbytes?

[John]

Thanks Steve for the awesome photo's and resources.

Can someone please check my math?  I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph.  In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k).  Plate max dissipation is 12W, B+ 350V. 

So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A).  Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point.   100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor.  This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result).  Yes?

This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve.  And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve. 

Am I understanding this correctly?  Have I drawn the load lines correctly?  I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?

If I'm understanding right, you've just forgotten to divide your pDiss by 2 tubes. Your data sheet is probably showing for 1 tube.

[sluckey]

I got a full set of knobs, tidied up the wiring a bit, and took a few more pics. I still don't have a good idea what this amp really sounds like other than it works as expected and is pretty quiet. Maybe by this weekend my blisters will be healed enough to try some loud guitar. I'll let you know if this amp makes me sound like Jimmy Page! 

[SILVERGUN]

Beautiful pics!
 
Now, if I could only get the picture of you soldering in your bathing suit out of my head....    

[sluckey]

Gimme your cell number and I'll send you a selfie!   

[Ed_Chambley]

That is just downright purdy!  I GOT BLISTERS ON MY FINGERS!


I have not has any dinner!

[CraigB]

Beautiful chassis!  Any plans for cabinet?  Combo?  Head?

[sluckey]

No plans for a cab. It's done. Did you find a switch? Digikey, Mouser, and eBay have the one I used.

[Joel]

Thanks for reponding John.  I don't understand your comment.  I've followed the method outlined by Merlin on his website for drawing load lines http://valvewizard.co.uk/pp.html  there's no mention of dividing max power dissipation by the number of tubes used.

Thanks Steve for the awesome photo's and resources.

Can someone please check my math?  I'm drawing a load line on the RCA 6973 datasheet Average Characteristics graph.  In this exercise I'm using the Hammond 290PAZ Marshall 18Watt OPT (8.4k).  Plate max dissipation is 12W, B+ 350V. 

So I draw the Max Dissipation curve, and the initial lines from 350V on the x axis, to 83mA on the y axis for 1/2 Za-a (class B), and 166mA for 1/4 Za-a (Class A).  Next is to find a nice bias point below the max dissipation curve, and apparently 70% is a safe starting point.   100% dissipation would lie on the max dissipation curve at 34.3mA, so 70% = 24mA and approximately -21V across the cathode resistor.  This would give a cathode resistor of about 440ohms (shared cathode resistor is half the calculated result).  Yes?

This means if I use a 250ohm cathode resistor as per the original schematic, I’d be at 100% dissipation and the entire load line would be above the max dissipation curve.  And, if I used an OPT with less load impedance (say 7.5k or 6.6k), all this would be even worse as the gradient of the line would be steeper and further beyond the max dissipation curve. 

Am I understanding this correctly?  Have I drawn the load lines correctly?  I feel like I’ve missed something, otherwise how did the original S-6424 amps not melt their output tubes?

If I'm understanding right, you've just forgotten to divide your pDiss by 2 tubes. Your data sheet is probably showing for 1 tube.

[Tony Bones]

Nice knobs!

Watching you build is inspirational!

[Ed_Chambley]

Inspirational or just Luckey?  Thats so punny.

[bnwitt]

Steve,
Absolutely bee u teeful.  First class amp porn!  Will there be sound clips?

[sluckey]

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

[CraigB]

Found the switch locally as well as the 500KL pot with switch.  I used to pretty much be able to buy everything I needed from this place, but the lady who ran it for years finally retired and sold it.  The new owner is cool, but the stock of things useful to tube amp building has dwindled to almost nothing.  What power tubes are you running there?  I can't tell from the pics.  Thanks again for documenting this build!  Very cool layout

[Sonny ReVerb]

Beautiful work, Steve! You're inspiring me to get going on my Ampeg build.

Now, if I could only get the picture of you soldering in your bathing suit out of my head...

Almost spit coffee through my nose  Wonder how this would sound through a Supro:

https://www.youtube.com/watch?v=OOgd9hitEAE

[sluckey]

@CraigB, are you going to build this amp? BTW, a 1M with switch works just fine for the Intensity pot. I'm running EH 6973 output tubes.

@Sonny, I think that would sound good through any amp! 

[CraigB]

@Steve - I'm gonna build it.  Ever since the Gretsch rebuild, I've wanted to do one of those, or the Supro. The trem on that Gretsch was one of the best I've ever heard, but it didn't have a depth control.  Dang, that's been like ten years ago, so a little slow to get around to it, to say the least.   

I've run across a couple negative internet comments about the EH 6973, but I am paying no mind to that whatsoever.  I've never had any problems with EH tubes not sounding good or being reliable.  I'm pretty sure that's what the new production Supros must come with.  So there to the naysayers.  Spend your money freely. 


And if you don't mind, I will be using your excellent layout, spaced a little different to allow for the size of Mallory 150 caps.  Hammond 16x8x3 should work since I won't have a PT cutout.  Using Heyboer replacement iron.

[sluckey]

I'll be interested to see your project. Others will too. I don't think you will have to change the board to fit the M-150s.

[bnwitt]

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

Oh Well.

[sluckey]

@CraigB, I don't know if you are committed to a particular chassis, but this project will easily fit into a 12.5 x 6.5 x 2.5 chassis, just like the chassis I used on my 6V6Plexi, L'il Maggie, and Dual Lite. And since you will be using a standup PT, you'll have even more room than I had in those projects.

I would have used the small chassis but I had a 17" chassis that I needed to use up. Anyhow, just a thought.

[sluckey]

♫ Duh-duh duh-duh duh! ♪

Finally had a chance to crank this amp. That early LZ sound is definitely there but at ear bleeding volume. So far I've tried a Celestion Blue, Weber California, and a 2x12 cab loaded with Celestion Heritage G12H(55) and Heritage G12H(75). The 2x12 sounds best to me. I plan to try some Jensen and Eminence speakers soon.

At moderate sound level the amp has an aggressive sound with a very noticeable compression. A good sound for most of the stuff I try to play. The sound cleans up a lot just by rolling the guitar volume back a bit. Even at low levels there is still a bit of compression. Wish I could describe the sound better but my ears just don't work well so I'm not sure my description is very meaningful.

The tremolo circuit actually modulates the gain of the first preamp tube. Very smooth and there's plenty of intensity and the speed range is good. I like it a lot better than the trem circuits that modulate the output tube bias or the typical neon/LDR roach.

Running both channels at the same time allows a much better range of tone settings. This will be the default setting for me.

Although I can now cover the opening to "Whole Lotta Love" it still doesn't quite sound like Jimmy. Probably just need a new set of strings! 

♫ Duh-duh duh-duh duh! ♪

[NO_H2O]

Yet another great build Steve. I'd love to hear it.

[Ed_Chambley]

♫ Duh-duh duh-duh duh! ♪

Finally had a chance to crank this amp. That early LZ sound is definitely there but at ear bleeding volume. So far I've tried a Celestion Blue, Weber California, and a 2x12 cab loaded with Celestion Heritage G12H(55) and Heritage G12H(75). The 2x12 sounds best to me. I plan to try some Jensen and Eminence speakers soon.

At moderate sound level the amp has an aggressive sound with a very noticeable compression. A good sound for most of the stuff I try to play. The sound cleans up a lot just by rolling the guitar volume back a bit. Even at low levels there is still a bit of compression. Wish I could describe the sound better but my ears just don't work well so I'm not sure my description is very meaningful.

The tremolo circuit actually modulates the gain of the first preamp tube. Very smooth and there's plenty of intensity and the speed range is good. I like it a lot better than the trem circuits that modulate the output tube bias or the typical neon/LDR roach.

Running both channels at the same time allows a much better range of tone settings. This will be the default setting for me.

Although I can now cover the opening to "Whole Lotta Love" it still doesn't quite sound like Jimmy. Probably just need a new set of strings! 

♫ Duh-duh duh-duh duh! ♪

New strings and a telecaster would give more bite on the bottom end. If you had your strat so you could run the neck and bridge and the neck blend pot.


Also, a strat is brighter if you are using the tone pot on a tele like seasoned tele players do. Tone knob centered roll up a little to get sparkle, drop back a little and get a nice power chord.


So you are saying to prefer the Celestine loaded SUNN cabinet? I think that is a great cab and I meant to get dimensions on that thing. That hampeg with that cab is really great. Great punch, so I would think the Supro would sound good too.


I believe it is 20percent speakers and 80 cab. I really like that SUNN stuff for build quality.

[adamG]

The power tubes were idling at 25 watts with the stock 250Ω cathode resistor. I've replaced that with a 470Ω to cool it off a bit at 17.8 watts.

Steve,

I confess I do not get the above math. Even, with cathode res.470R you'll receive approx.19,5W.
Could you expound your calculation, please?

Thanks in advance.

Regards,

Adam

[sluckey]

I assume you used the voltages from my schematic? Did you forget to subtract the cathode voltage from the plate voltage to get the real plate voltage needed for the calculation?

[adamG]

I assume you used the voltages from my schematic? Did you forget to subtract the cathode voltage from the plate voltage to get the real plate voltage needed for the calculation?

Actually, I've made a silly mistake .Now, I can see that ,I perceived on schematic 374 V instead of 347 
For now ,it's perfectly ok.

Thank you Steve!

Kind regards,

Adam

[MFowler]

Steve,


Such a clean good looking amp.


Mark

[sluckey]

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. Here's my lame attempt at sound clip using cell phone and MP4 to MP3 converter software. Please don't tell Jimmy!   

http://sluckeyamps.com/supro/test.mp3

[John]

All that needs yet is a picture of you in your bathing suit. 

[sluckey]

I ain't ready to give it all away yet!   

[davidwpack]

Can I ask where you got your fuse holder? I don't recall having ever seen one like that. It looks pretty nifty.

[sluckey]

That fuseholder was very common in military/industrial equipment. The twist in cap has a neon bulb in it which will illuminate when the fuse is open. Look in government surplus or industrial electronics supplier catalogs, or eBay. Do not get one of the low voltage holders.

[SILVERGUN]

I was just about to start handing out defensive ass-whoopins for you, like
"he's done 24+ amps and never posted a sound clip, please stop pressuring him.....if he wanted to post a clip he would. Do you think you're the first one to ask?"
..and then you go and post one.
Love it!...I can definitely hear that Zep quality in there.
I'm assuming that was recorded with your Strat?
I agree with Ed that the Tele would be the magic ingredient.

Now, get busy with those other 23+ clips you owe us