Supro 1696TN

[scstill]

Been fabricating the cabinet and split chassis(s) for the Supro 1696TN.
Can see build progress at https://stillampd.com/supro-1696tn-repro
Now its time to begin wiring.  The only real available schematic was hand drawn by Bill Kahle (not in EL34 schematic library but included below). I also have a hand drawn from Leon C that I could post but its very hard to read. anyone have another source?

The schematic has a significant error that I wanted to confirm.
The 6L6 grid is switched with the screen.
Notice that the HV is applied to the grid and the input is on the screen.
Unless I'm missing something this is backwards. I believe that the pin numbers are correct

[Latole]

Same as Gretsch 6163 ?
 
https://schematicheaven.net/bargainbin/gretsch_6163.pdf

[sluckey]

The 6L6 grids is just a little thing, but that Kahle tremolo circuit is definitely WRONG. Look at the Gretsch schematic Latole posted to see how to unravel the Kahle drawing.

EDIT... I must have been looking at the tremolo circuit with crossed eyes! Looking closely today I see that the circuit is drawn correctly. Sorry.

[bmccowan]

I also have a hand drawn from Leon C that I could post but its very hard to read.

If you want to post that one from Leon, I'd be happy to try and decipher it and redraw it in ExpressSCH. I have an incomplete basket case of that amp waiting in the wings - enough of it is intact that I can use the parts to confirm pieces of the schematic. Leon knows his way around those Valcos, so I'd be pretty confident that his schematic is correct.

[scstill]

Here is LeonC schematic. I will be taking closer look after seeing the Trem issue with the Kahle Schematic
LeonC Schematic was also posted at https://el34world.com/Forum/index.php?topic=26740.msg293624#msg293624

[sluckey]

Here is LeonC schematic. I will be taking closer look after seeing the Trem issue with the Kahle Schematic
It was also posted here https://el34world.com/Forum/index.php?topic=26740.msg293624#msg293624

There is no issue with Kahle's trem circuit. It's all good.

I've redrawn Kale's schematic in a more logical drawing using Visio. I'll compare to Leon's schematic and probably post tomorrow.

[PRR]

...a hand drawn from Leon C that I could post but its very hard to read. ...

Somebody needs more ink in his pencil. Or his scanner.

I dunno if this is better or just less squinty.

V6 is missing a grid resistor. 270k like the other side makes sense. The 0.01u/0.02u grid caps don't makes sense to me but maybe the factory was trying to use-up ALL their parts.

[sluckey]

More ink...

Edit... Updated schematic now includes single chassis layout

[bmccowan]

Well that's a big improvement - I started redrawing Leon C's schematic in ExpressSCH. I'll finish and compare to Sluckey's Visio drawing. So far - its very similar to other Valco 2x6L6 models - no surprise.

[sluckey]

The trem channel and power amp are almost identical to my S-6424. Actually, identical circuit with very few slightly different component values. I was able to easily modify my existing schematic. Leon's schematic had one error that PRR spotted and there is one small error on Kahle's drawing.

[bmccowan]

I finished the Express SCH drawing this morning. I like Steve's Visio drawing better but I have not used Visio in 20 years - maybe I'll start again. As near as I can tell Steve's drawing nails the Leon sketch, and I think this one is identical. But I usually make a mistake or 3. So we'll see. I added Leon's notes for mods, but its a bit confusing as to which value was the chicken and which was the egg. I'd experiment with both if I was building it.
Edit - I went to Leon's YouTube channel and found this:

Looking at my old notes, looks like most of what I did was on the trem channel. The switch there provides alternative ground reference options for the first triode. I replaced the 1M resistor there with a 2.2M. There are two .005uF caps coupling the first triode to the next stage. They were replaced with .02uFs. There's a 270K ground reference between them; I added a 500pF cap in parallel to prevent oscillation due to the extra gain I've induced. I changed the 150K grid leak in front of the PI to 270K. There you go!

Edit - fixed the mistake Sluckey found

[bmccowan]

jpg not displaying - but opens

EDIT... Fixed attachment

[sluckey]

Just like Leon, you forgot the 470K grid leak for the bottom 6L6.   

[bmccowan]

Just like Leon, you forgot the 470K grid leak for the bottom 6L6.   

yes I did - its leaking as it should now I think. Thanks for noticing.
But I must also be doing something wrong when posting the jpgs?

[sluckey]

I just opened your jpg file in Paint Shop Pro (PSP) and then I saved as jpg file. PSP cleaned it up.

Tell me exactly how you get from Express SCH format to jpg format. I want every little detail.

[bmccowan]

Tell me exactly how you get from Express SCH format to jpg format. I want every little detail.

OK - first I move my mouse toward...
1. I export the file to a 200 pixel bitmap image.
2. Open the bitmap image.
3. Save the bitmap image as a .jpg file

[sluckey]

What program do you use to open/save your bitmap file? If using Windows native photo program, then try another image program. If you want a good free image program then download Irfanview. Very good.

     https://www.irfanview.com/

[Latole]

I just opened your jpg file in Paint Shop Pro (PSP) and then I saved as jpg file. PSP cleaned it up.

Tell me exactly how you get from Express SCH format to jpg format. I want every little detail.

With my Mac I clic on the file and I see it.

[bmccowan]

I am using a Windows native program - I will give that a try Steve - thanks

[uki]

This is a very powerful image editor and will probably get things right!

www.gimp.org

Bad Windows...   

I call it Ruindows

[scstill]

Thank you all for your assessment of the hand sketched schematics.
This forum now has some great 1696 schematics that could be hosted for others in the forum library (if possible).

I have another issue with this build.
I am planning to add a Fender Twin Reverb reverb circuit with a 9AB1C1B tank I have laying around. This is my 1st reverb build.
Reverb is already mounted in the cabinet along with custom bag and RCA cable from tank to upper chassis.
Two questions:

1) Footswitch - I am planning a Stereo Switchcraft shunted jack and was hoping to wire like my Silvertone 1484 which is grounded to chassis (BTW - thanks Tubenit for that footswitch still working great). But the 1696TN shows a .02 cap before ground. is this to eliminate pop when removing the Footswitch plug? Could I eliminate? or would it work for both the tremolo and reverb?

2) High Voltage - the Fender Reverb Drive (schematic below) shows 440v on the drive plate. But as designed, the 1696 circuit only sends about 320V to the upper chassis (C output from PS). Does the Reverb need the 440? And if so since I only have one HV line would I be ok to take the B output and the drop the voltage for the other 12ax7 plates in the upper chassis??

[sluckey]

I don't know why valco did the footswitch like that. Stupid idea IMO. Easy fix though. Look at this schematic and modify your circuit to match the footswitch connection...

     https://el34world.com/charts/Schematics/files/Supro/Supro_s6616.pdf

The Fender reverb driver wants a lot of B+. Afterall, it is a little single ended power amp. I suggest using the screen node to send B+ to the upper unit. This will easily power the reverb driver. But you will need to add a dropping resistor and a filter cap to feed your preamp circuits. Should be pretty easy to do.

[shooter]

fwiw;
WIN10 has something called a snipping tool, type it into tool search bar.
whatever you have displayed you can draw a box and save as jpg.
works great for "screen captures" from the net.

[sluckey]

Been fabricating the cabinet and split chassis(s) for the Supro 1696TN.
Can see build progress at https://stillampd.com/supro-1696tn-repro

Got a couple questions for you...

What is the width (long side) of your preamp chassis? And what is the width of the control panel cutout on top of the amp?

BTW, I just took a tour of your website. I really like the projects you've done, especially those radio conversions.

[PRR]

jpg not displaying - but opens

It originally said .JPG but was really a BMP. That was an OK format, in 1989. Don't do that!

The .jpg filename and .bmp contents confuse the forum thumbnail tool. In the past it might confuse browsers. Today's browsers ignore the extension and make their own guess, so it mostly displays OK.

BMP is rarely compressed. (It comes from days of slow CPUs.) Note that in Sluckey's trio, the BMP (black thumbnail) is much bigger than the others.

IMHO, JPEG is BAD for clean line-drawings. Eventually the whole world will drown in JPG blurr. Clean B&W images render terrific in GIF, and compactly.

Today (I wish you had not edited in place) some of the black-thumb images images are PNG. That can be a good plan, but again the thumbnail tool is baffled and delivering a big black dot.

Below is the image as a GIF. It is 1/8 the size and has no extra fuzz.

Decide what file-type (JPEG for nudies, GIF for line-drawings), and be sure your filename extension matches. Not everybody (not even program tools) knows how to look inside the files for the true filetype.

[bmccowan]

PRR - that gif looks nice and clean. So I want to make sure I understand you. Since ExpressSCH only exports to .bmp an amended process from what I responded to Sluckey would be?:
1. Export the file to a 200 pixel bitmap image.
2. Open the bitmap image.
3. Save the bitmap image as a .gif file
I just did that with another sch file and it looks very good.

[PRR]

> Open the bitmap image.

With what? I have PaintShopPro, Sluckey has same/similar, Irfanview is a good tool.

I don't trust MicroSoft Paint even for MS's/OS2'2 own file formats (there are many).

And THEN there are image-hosting outfits which refuse GIF, or silently convert to a blurry JPG.

[scstill]

Been fabricating the cabinet and split chassis(s) for the Supro 1696TN.
Can see build progress at https://stillampd.com/supro-1696tn-repro

Got a couple questions for you...

What is the width (long side) of your preamp chassis? And what is the width of the control panel cutout on top of the amp?

BTW, I just took a tour of your website. I really like the projects you've done, especially those radio conversions.

Thanks for the website compliment. Means a lot to me. There is a lot of EL34world knowledge in those builds.
They sound really good too. Hoping to add some sound clips to the site soon.

The preamp chassis length is 21.5". The cabinet opening for the control panel is 17" x 2.75" (to the inside of the back panel).

I did alot of research on the 1696 cabinet and chassis. I did not have a model to measure and so used pictures and scaled the dimensions as best I could. BTW - this is the Supro slant cabinet (front and back) it is really a great look.
This is my first try at building a cabinet (my son cut the fingers and rounded the edges and cut the front and rear panels). Also first try at bending chassis' After building the lower chassis I decided to add the reverb and so I had to unbend and re-bend a narrower chassis. Next time I will go for lighter gauge :-)

[scstill]

The lower chassis is now wired up.
mods based on this forum: 1) split chassis cable socket is on the lower chassis. Hole patched in upper. 2) Higher voltage for reverb drive is sent to upper chassis with preamp dropper upstairs, 3) for the footswitch - going with the standard dual footswitch wiring rather than Supro.

And the footswitch is fabricated and wired. May need to upgrade the switches as they don't have a real good mechanical feel to them. Also I used a microphone cable for the footswitch with the shield as the ground.

More description here:
https://stillampd.com/admin/edit-content/supro-1696tn-repro

[sluckey]

Your footswitch looks just like the FS for my old Sears 1484 amp. And my 45 year old GE range hood used those same style switches for the light and fan. Still working fine when I recently upgraded the hood.

[scstill]

Your footswitch looks just like the FS for my old Sears 1484 amp. And my 45 year old GE range hood used those same style switches for the light and fan. Still working fine when I recently upgraded the hood.

I also have a Silvertone (Sears) 1484; great amp that gets played alot. Tubenit provided the footswitch that I was missing (an exact match from Danelectro). That switch provided the inspiration. This will match the Supro 1696 repro, and there is an excellent storage spot between the PT and the cab wall.

[scstill]

As mentioned earlier, I plan to include the reverb circuit from the Fender Twin Reverb AB763 in this Supro 1696TN Repro.
1) Should I use the Second triode of the 12ax7 Reverb Recovery tube as a gain stage as the AB763 does?
2) is the correct place for the reverb circuit at Pin 2 Grid of the V2 PI tube of the Supro 1696?

[sluckey]

I think you will have a lot of challenges trying to adapt an AB763 reverb circuit to this Supro. I suggest you look at tubenit's one tube reverb circuits. I believe you will have better results and fewer headaches. Maybe tubenit will join in and offer some suggestions.

[tubenit]

This is the reverb that I have in my Carolina Overdrive Special.  You could try it and see if you like it.  IF you need more reverb try increasing the cathode cap on the send triode from 10uf to 22uf.  IF you need more reverb than that you can change the reverb pot from 1M to 2.2M.

I'd try a 12DW7 first.

I have an amp with AB763 type topology using a paralleled send triode and this one with one tube reverb. At the level I play reverb, this one tube reverb sounds as good or better to my ears. 

I am NOT familiar with the phase invertor in this amp, but I am not aware of any reason why this wouldn't work either?


Oh, I'd also create a node D and use that for the reverb send and return triodes. You could just use 20uf.      * see attached   

With respect, Tubenit

[scstill]

Thanks for the reverb considerations...

1) Leaning toward the single tube approach which will leave a spare 9pin socket in the chassis.
Just leave it empty? Or is there a clever use for it?

2) Why a separate D node? isn't that the same as the C Node?
Recall that I have a split chassis cable and am sending only one HV to the upper chassis.
So My plan was to send B (or as recommended D) to the upper and then drop to C upstairs.

3) Does anyone know why Ab763 used an additional triode gain stage for the reverb before sending to the PI?
Wouldn't that give a higher signal than the normal channel?

[sluckey]

1. Just put a button plug in the hole for now.

2. As is, there are six triodes being fed by Node C. Don't need to pile on more. But rather than making a Node D, I would first try rearranging the nodes. I would use Node C for V1, V2, and the reverb recovery triode. That's five triodes on Node C. Use Node B for V3 and the reverb driver triode.

3. See that 3.3M mixing resistor just prior to the additional triode? That knocks the crap out of the dry guitar signal prior to mixing with the reverb signal. The third triode is needed to boost the guitar signal back up.

[scstill]

As is, there are six triodes being fed by Node C. Don't need to pile on more. But rather than making a Node D, I would first try rearranging the nodes. I would use Node C for V1, V2, and the reverb recovery triode. That's five triodes on Node C. Use Node B for V3 and the reverb driver triode.

Thanks for the advice:
I  could run the B node to the upper chassis. Can I use that direct for the Reverb Drive or does it need its own RC?
Or I could run A to the upper and create a D node

Still wondering if I would lose the Supro sound if I don't keep V1, V2 and V3 together
Otherwise, What do you think about three parallel C nodes off the B: C1 for the V1 and V2; C2 for V3; and C3 for Reverb Recovery. That keeps the tremolo and reverb separate if that would help. And Unless channel 1 and 2 are patched there is only two triode on C1.

I read the AC30 post (https://el34world.com/Forum/index.php?topic=17349.msg173718#msg173718 #8) by EL34 where they give every tube its own node.

[tubenit]

I don't remember who posted it and where I read it, but I remember someone saying part of the "Supro tone" is the under filtering in the B+ rail.  So, my thinking is leave all that the same as on the original schematic.

However, you are wanting to add a one tube reverb.  So, my thinking was leave the original filtering for the original triodes alone.............. BUT add one more filter cap for the reverb tube.  That's why I suggested that and took the time to draw up a schematic to illustrate what I was saying.

This doesn't mean you "should" use my suggestion. I simply put it out there because it made sense to me and is how I would approach this.

Sluckey gave you a reasonable suggestion also.  You have added a 3rd option.  Pick one and let us know how it turns out.

With respect, Tubenit

[sluckey]

Updated schematic now includes single chassis layout. See reply #7.

[scstill]

Relative to the original filtering comment. In Kahle schematic on B node there is two parallel 20uf whereas in LeonC there is 20 and 10. Same as the redrawn schematics. Anyone know which is original? I wired up as two 20s. Does this matter?

[sluckey]

I don't know the answer. Might be able to tell from some good pics. It's more common to see the largest cap at Node A.

[sluckey]

Take a look at the S6622 schematic. I would use this reverb schematic. The fender reverb tranny and pan will work well in this circuit. Guaranteed to sound like a Supro. 

Also, notice the filter cap arrangement.

[scstill]

Updated schematic now includes single chassis layout. See reply #7.

This is great I love the chassis layout. Wonderful software tool that you have.
Couple of things:
1) where might I go for a graphic for the top panel? would I have it custom made? or go with my own printed water slide, dry rub or self stick?
2) My layout is slightly different that the original (pic below) as I added the reverb control to the top panel and moved the footswitch out of the way to the underside of the upper chassis and also moved the fuse and on/off to the lower chassis to avoid having mains power cabled between upper and lower. A slight inconvenience for the player, but easier (and maybe safer) to design.
3) on your layout the pwr supply A to B resistor is shown originally as 7w (10w in the redrawn schematics) which might need a bigger space on the layout. Maybe also for the 5w B to C resistor.
4) I used the 1760J as the OT and the 274AX as the PT (I could not see PT called out on your layout), The PT was based on info from Terry Dobbs (friend of LeonC) who pointed out the Orig Valco PT was E-3738A and Magnetic Components made the 40-18060 as a replacement. The 274AX is a close match to the classictone.
5) I love the circuit board layout, although I have not done one yet, but soon. This 1696 repro will be point to point wired with terminal strips as needed to match the original. Any advice in this regard?

[scstill]

Take a look at the S6622 schematic. I would use this reverb schematic. The fender reverb tranny and pan will work well in this circuit. Guaranteed to sound like a Supro. 

Also, notice the filter cap arrangement.

Thanks for this. For sure a Supro reverb circuit will sound more like a Supro :-)

In the S6622 It seems that V1b is used as pre-reverb gain before V2 Drive. Wonder why??
Then like the AB763 there is a post reverb (and dry) gain with V3b.
Although the Supro dry here only sees 470k resistor vs Fender at 3.3M.

If I do go with the S6622 reverb I will only have one spare triode. Would it be best served for Pre-gain? or Post gain?

[sluckey]

Couple of things:
1) where might I go for a graphic for the top panel? would I have it custom made? or go with my own printed water slide, dry rub or self stick?
2) My layout is slightly different that the original (pic below) as I added the reverb control to the top panel and moved the footswitch out of the way to the underside of the upper chassis and also moved the fuse and on/off to the lower chassis to avoid having mains power cabled between upper and lower. A slight inconvenience for the player, but easier (and maybe safer) to design.
3) on your layout the pwr supply A to B resistor is shown originally as 7w (10w in the redrawn schematics) which might need a bigger space on the layout. Maybe also for the 5w B to C resistor.
4) I used the 1760J as the OT and the 274AX as the PT (I could not see PT called out on your layout), The PT was based on info from Terry Dobbs (friend of LeonC) who pointed out the Orig Valco PT was E-3738A and Magnetic Components made the 40-18060 as a replacement. The 274AX is a close match to the classictone.
5) I love the circuit board layout, although I have not done one yet, but soon. This 1696 repro will be point to point wired with terminal strips as needed to match the original. Any advice in this regard?

1) I just use a Dymo PnP label printer. I used black type on clear tape for my Supro. Good enough for me. There are lots of website services that can make a faceplate from your artwork. Many members know more about that than I do. Sign shops, trophy shops and print shops can also do custom stuff from your artwork.

2) Your changes make good sense to me.

3) I did some power calculations based on an estimate of 10mA screen current and another 10mA for the three little tubes. 3 watt resistors should be fine for both of those droppers. Heck, I only used 2 watt resistors in my Supro.

4) I put the 1760J on my layout mainly for a size reference. I recently used that OT in a 6L6 push/pull amp and I know it's a good choice for this Supro. I didn't bother to specify a PT because I ain't gonna build this. My preference would be a standup style PT. I'll take a look at the 274AX.

5) I don't envy you building a PTP circuit in that skinny chassis. Better get it right the first time and hope you never have to fix it.   

The S6622 only uses two tubes for reverb and you have five sockets. Sounds just right to me. Get the circuit worked out before you drive any nails.

[sluckey]

This is how I would add that S6622 reverb to your 1696TN. No warranty.   

[bmccowan]

5) I don't envy you building a PTP circuit in that skinny chassis. Better get it right the first time and hope you never have to fix it.   

I have rewired a few Valcos and I admire the way they bent the resistor leads uniformly like sawtooths to make neat terminal strips. But, they are a bitch to work on with solder joints hiding behind components. I was constantly putting burn marks on wires and such. So if you are going to go that route, I'd suggest maybe soldering up the terminal strips in modules before securing them to the chassis. Another consideration is that resistor and cap leads are not as robust as they used to be, so point-to-point wiring is not as solid as it used to be. But your photos show that you do great work, so you'll likely find it easier than I do.

[scstill]

Thanks for all the advice and suggestions. I learn a lot from your experience.

Here is my next step, I made adjustments on sluckey redraw for the footswitch and upper chassis pwr.
I typically count the number of connections that need a terminal (T) after connecting to pots and sockets.
My draft below for strips for each stage.
In addition to challenge of narrow chassis, this one is almost 4" deep. So I was thinking of using standoffs to avoid the deep dive.

BTW - did you notice the unique upper chassis side profile? Because the front and back of the cabinet is slanted the upper chassis needed to be angled to be flush with the cabinet angle. I suppose I could have picked an easier first chassis bend. :-)

[martiro7]

The lower chassis is now wired up.
mods based on this forum: 1) split chassis cable socket is on the lower chassis. Hole patched in upper. 2) Higher voltage for reverb drive is sent to upper chassis with preamp dropper upstairs, 3) for the footswitch - going with the standard dual footswitch wiring rather than Supro.

Wow! Where did you get your Amphenol style umbilical plug/socket? I've been hunting, to include even eBay, to try and source something that would do for my 1696 build.

[sluckey]

How hard did you look?   

https://www.tubesandmore.com/products/plug-8-pin-octal-tube-base-black-plastic

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=male+8+pin+octal+plug&_sacat=0&LH_TitleDesc=0&_odkw=male+8+pin+plug&_osacat=0