Supro S6424 project

[sluckey]

I've finally started this project. All parts have been received and the build is under way. I'll eventually make a web page for this amp, but I have a lot of other stuff going on right now too. Meanwhile, here are a couple pics of completed chassis work to give you an idea what it's gonna look like...

EDIT... here's the layout document...  http://sluckeyamps.com/supro/supro.pdf


 

 

[shooter]

Nice as always!  I'm looking forward to getting your take on the 1 knob tone n if you tweak it.  I need to get my project from a 2 knob to a 1 knober, so please don't patent it yet

[sluckey]

The 6424 has two tone knobs so I won't be tweaking for one knob. Look at the 1624 schematic if you want to see the one knobber version of this amp.

[shooter]

6424 has two tone knobs

the schematic you posted on another thread shows 1 knob for each side of V1, so ya 2 total, same as I'm thinking of doing, currently I have 2 per side.

If I looked at it correctly they are the same 500pf, .0033uF, 500k.
I'll steal that as a starting point.

[tubeswell]

Subscribed.


Hi Steve - what VA rating is that variac on your bench BTW? (if you don't mind me asking - only it looks like of compact/smallish - like 500VA or something. I was wondering about picking one up for myself, but didn't think that 500VA would be big enough. If it is 500VA, how do you find it for your stuff?)

[Joel]

Excellent!

[sluckey]

Hi Steve - what VA rating is that variac on your bench BTW?

It's rated for 0-140V and 10 amps. I sold a 5 amp Staco earlier this year. 5 amps is big enough for everything I've messed with. 10 amps is what I've seen mostly in the old repair shops. If I had to buy one I'd shop for a 10 amp model. A built in volt meter is very handy too.

[Tony Bones]

And, if you would like a variac that does not hum and vibrate, then get one rated for 240V and run it on 120V. Unfortunately, the current rated does not double, it stays the same.

[MFowler]

Steve,


Great looking project looking forward to this.  I had a custom 1-15 cabinet built and will be tackling a Supro T-bolt one of these days.


Mark

[sluckey]

Thanks Mark. I've been following your project over on TAG with interest. Looks good too.

[PRR]

> 10 amps is what I've seen mostly in the old repair shops.

The original GR Variac was rated 10A. Many clones were also. In days of 15A circuits, a 10A would handle nearly any load. The "10A" is conservative and you can beat it considerable for occasional use/abuse.

Smaller ones don't want to cost a lot less-- wire core and labor don't scale-down real favorably. Of course smaller/larger ones did appear, under 2A to over 30A. I just got a 5A which I plan to use on a 3.6A furnace blower where it may be loaded 23 hours a day. (I ended up with the small fan on the extra-small burner and it blows a lot of hardly-hot air; I can reduce the blow for the same heat in warmed air and less draft.)

[sluckey]

Got the board built today. Too hot to do any more...

[EKDENTON]

Real nice looking so far! You always make nice neat looking amps!

[sluckey]

I got the board laced and loaded today...

[Ed_Chambley]

Man you just throwing all the mojo out.  MF Resistors, Illinois caps, and Chicklets?  Have you gone mad sir?  You know it will now sound like a modern Mesa Boogie, is this really what you want being an old surf junkie?


How hot is it?  Why didn't you air condition your workshop?  You've got enough money to air condition a cotton field there in LA.


Is this where you play guitar too?
 


Looks great and really a fun amp.  The tremolo is outstanding.  Is that Black Fiberglass Board? It looks like it has graphite on it.


The lone turret under the pot on the front of the chassis, did you not drill through?  Use a bottoming tap.  This support for your preamp ground bus?

[sluckey]

Man you just throwing all the mojo out.  MF Resistors, Illinois caps, and Chicklets?  Have you gone mad sir?  You know it will now sound like a modern Mesa Boogie, is this really what you want being an old surf junkie?

I've set my sights pretty high on this one. I'm gonna be able to play the opening to "Whole Lotta Love"! 

How hot is it?  Why didn't you air condition your workshop?  You've got enough money to air condition a cotton field there in LA. Is this where you play guitar too?

Low 90s with matching humidity. I'm still trying to raise money for an AC unit. Not to worry though. The pool is only 20 steps away. And I have a refrigerator in the shop. I prefer to do amps during the winter.

Is that Black Fiberglass Board? It looks like it has graphite on it.

Yes. Got it from Doug. He calls it FR4/G10. It drills and cuts easier than his green board. The board is jet black but the fluorescent lights put a "washed out" sheen on it. Haven't been able to get a good pic.

The lone turret under the pot on the front of the chassis, did you not drill through?  Use a bottoming tap.  This support for your preamp ground bus?

The turret is soldered to the back of the pot. It supports the two mixing resistors from the two volume pots. Look at the layout and schematic.

[shooter]

I'm still trying to raise money for an AC unit.

I got an 8ton unit with a couple issues, but it's free

[Ed_Chambley]

I see the Visio work now, you added it.


Your schematic drawing is much easier and logical to read, but it doesn't show a switching pot.  It took me a bit to find the shared cathode site you have them reversed.  Are you planing a pull pot to slow the tremolo even more or is it simply to stop and start?


I see you have a switching dual input.  I do this a lot now myself ever since the AC15.  Just a simple thing, but it adds so much to the tonal versatility to an amp.  Since the wiggle channel has more gain and headroom, I am surprised you duplicated the tone stack.


I wish I could play    Even if it were only Whole Lotta Love.  Finger doesn't look a lot better yet.  120 grit on a belt sander will remove fingernail and skin quick.  I just hope it quits bleeding in a day or 2.


Nice work as always!

[Ed_Chambley]

I'm still trying to raise money for an AC unit.

I got an 8ton unit with a couple issues, but it's free

Shooter, he is full of more crap than a Christmas Turkey!


Trying to raise money.  Yea, I believe that.  No, he is just used to the Mobile area where when it is not hot, you better leave cause a hurricane is on the way.  I hear the older you get the more you prefer the heat.  I also hear you ears do not quit growing and I already have plenty.

[sluckey]

I got an 8ton unit with a couple issues, but it's free

Couple issues??? Are you saying it actually took two lightning strikes? 

[sluckey]

The pot switch simply turns the trem on/off. Just trying to keep it true to the schematic but mostly it's s good way to mount that 2.2M resistor. 

I got my index finger jammed between a disc sander and the sanding table on my ShopSmith once. It came out once I had sanded it enough.

[sluckey]

Looks like all I'll get done today is the filament string.

[shooter]

It came out once I had sanded it enough.

You folks need to sand like you build amps

two lightning strikes? 

I wasn't counting, I wasn't seeing very well either!  I was upstairs, 30ish ft away when it struck!!  The next morning my eyes felt like I had flash burns from welding!  It also hit 3 apple trees that had been on the property since late 40's.  They have lost most of their bark, most of the upper growth, but still got a bumper crop growing for the resident deer.

[pompeiisneaks]

Wow I've missed this much of your build Steve!  Good to see another amazing build coming together.  But I do see one error.  You've got the red and black wires used for heaters when they should be green and white! :P

Look forward to the finished product!  My first ever real time sluckey build. 

(I missed the first due to being on vacation in Scotland, so I guess that's acceptable :D)

~Phil

[sluckey]

I prefer green/yellow and would really love to have some brown. But I have limited quantities of those colors. Got miles of 20AWG red and black Teflon though! That's the main reason I use it. Plus it makes all the Marshall freaks happy! 

[sluckey]

Got the control panel wired today...

[SILVERGUN]

Beautiful, inspirational work, as always.. 
Love the way you are able to work patiently and just chip away at it. I always get so damn excited I just work and work until my eyes hurt and I need a massage.
 
I noticed a small discrepancy in your schematic.
The cathode bypass cap on the input triode ("Z" feed from the tremolo) appears to be 35uf/50V on the original, but .0033 on your schematic. I see where you have a 35uf on your layout, so I'm sure it's just a typo.
 
I found this while comparing values and circuit structure to the 1624T model.
This 6424 and the 1624T are basically identical.
 
Your documentation is always perfect and I want to keep it that way 

[sluckey]

Thanks for catching that. Got it fixed already. As always, if you find any discrepancies or other little turds please let me know.

I'm not really being patient on this project. I would be done by now if I had waited until winter to do it. But I got the hots to do it right now. And that's the problem. It's too damn hot and sticky in my shop to stay on the bench for more than a couple hours! I'm working in a bathing suit so I can jump in the pool with a beer. I usually don't make it back to the shop after that! 

[CraigB]

Thanks for catching that. Got it fixed already. As always, if you find any discrepancies or other little turds please let me know.

I'm not really being patient on this project. I would be done by now if I had waited until winter to do it. But I got the hots to do it right now. And that's the problem. It's too damn hot and sticky in my shop to stay on the bench for more than a couple hours! I'm working in a bathing suit so I can jump in the pool with a beer. I usually don't make it back to the shop after that! 

Nice project Steve, I've been wanting to build a PP 6973 based amp ever since I "restored" a Gretsch 6161 a few years back.  Looks like pretty much the same beast to me.  The guy had two of them, one that was completely thrashed (mostly the cabinet and speakers, which looked like they had spent some time underwater) and the other amp was in half decent shape, so he commissioned me to salvage the parts that were in the best shape from either and make them into one functioning amp, and whatever was left was spare parts.  So I had never heard played on one of these until I finished the project.  Very impressive little amp and very fun to play.  I must say, I didn't want to deliver it back to him! 

[sluckey]

I must say, I didn't want to deliver it back to him!

That sounds encouraging. Thanks for the info Craig. Thanks for the kind words as well.

[shooter]

ok, I give, is that standoff soldered?

and

jump in the pool with a beer

doesn't that water down the already thin beer

[sluckey]

ok, I give, is that standoff soldered?

Yes. The bottom threaded part is brass. Solders very easy even with my little Weller iron. Just gotta use flux and pre tin the turret and the back of the pot.

[tubenit]

Been following this build with interest.  Looks like  fun project!

With respect, Tubenit

[adamG]

Steve,

Regarding my topic of 1624, what power output with your 6424 are you gonna receive?
I think ,I'll follow my build with quartet tube power stage and remain with biasing cathode resistor or resistors.

Regards,

Adam

[sluckey]

I'm expecting about 15 watts.

[adamG]

Acc.to 6973 data, It should be approx. 17W with 300V at plates.
On schematic we have 350V. So, It might be even more?

Regards,

Adam

[MFowler]

ok, I give, is that standoff soldered?

Yes. The bottom threaded part is brass. Solders very easy even with my little Weller iron. Just gotta use flux and pre tin the turret and the back of the pot.

Haven't seen that before, very neat idea. I use a lot of those turrets and think I'll still just drill a hole and bolt mine on, I'd probably cook the hell out of the pot.


Mark

[shooter]

Haven't seen that before, very neat idea

agreed, does seem a waste of good threads though

[sluckey]

Got the input selector, shielded cables and PT wired this morning. All PT voltages checked out OK. Probably won't get back on this until Monday. Got some dignitaries coming to Mobile this weekend.

[pompeiisneaks]

Got some dignitaries coming to Mobile this weekend.

In Laws? :)

~Phil

[sluckey]

No, they're outlaws! At least one is. 

[John]

The best kind bring 'shine.

[bnwitt]

Very nice Steve

[Joel]

I'm building vicariously via this thread.  It's looking very nice Steve, and I'm finding nice little touches of yours to steal to include on my build.

Speaking of little touches... On your schematic you've got a 1M input resistor, but the layout has 470K.  The original S6424 schematic uses 470K, so I imagine you're also using 470K?  I can't tell from the latest pic...

I'm interested in what output transformer you'll use.  I'm pretty much restricted to the Hammond line of output transformers unless I want to pay an arm, a leg, and my first born to pay shipping from the States.  The Electro-Harmonix 6973EH datasheet gives 17 Watts from 310V plate voltage, 270R Cathode Resistor and 6k load.  The closest Hammond Output transformer would be the 1760H, 6600 ohm CT, 20W.  Of course, this circuit runs the plates a wee bit hotter... 

It's the same story with the power transformer.  I'm liking the Hammond 290BEX for this.  315-0-315, 138mA primary.  I reckon this'll give me a B+ of around 350 to 370V when using a 5Y3. 

I'll need to break out my books and draw some load lines to figure the difference all these little differences will make.  250R, 310V, 6k vs 270R, 370V, 6.6k.  Or are all these values close enough for rock n' roll?

[DummyLoad]

the hammond 1650F 7.6k 25W OT is closer to the original supro part which is 7.5k.   


the 290BX will generate about 375V.



--pete

[sluckey]

On your schematic you've got a 1M input resistor

Thanks for finding that error. I've corrected it.

I'm using a PT and OT from a donor Hammond AO-43 amp.

[Ed_Chambley]

The best kind bring 'shine.

And they may bring some of that wacky weed too.

[Ed_Chambley]

On your schematic you've got a 1M input resistor

Thanks for finding that error. I've corrected it.

I'm using a PT and OT from a donor Hammond AO-43 amp.

Do you know the reflected impedance on the Hammond OT?  I guessed they were 10K/8ohm, but I have never known for sure.

[sluckey]

Voltage ratio is 1.025:30.6 or 29.85.
Impedance ratio is 29.85 x 29.85 = 891.

So, 8Ω would reflect 8 x 891 = 7128Ω plate to plate. Looks like a good choice for 6973s.

This OT was used with a pair of EL84s in the AO-43 amp and the same OT was used with a pair of 6GW8s in the AO-44 amp. And I used the same OT in my Plexi6V6 and L'il Maggie projects.

[jojokeo]

Voltage ratio is 1.025:30.6 or 29.85.
Impedance ratio is 29.85 x 29.85 = 891.

So, 8Ω would reflect 8 x 891 = 7128Ω plate to plate. Looks like a good choice for 6973s.

This OT was used with a pair of EL84s in the AO-43 amp and the same OT was used with a pair of 6GW8s in the AO-44 amp. And I used the same OT in my Plexi6V6 and L'il Maggie projects.

These are perfect for all of those tubes mentioned. I really like them (the Hammond iron). I've also used it for 6BM8s with much success.

Steve, you inspired me to create an amp conversion recently, as many of your amp projects have - and I'd just like give a big thank you for this along with all of the responsive help you provide.