Supro 1688TN scratch build

[luthierwnc]

Hi All,

I'm in the design phase of my winter project.  Thanks to the amazing vids by leonc I thought I'd make a serious run at the Supro 1688TN.  This will be a head to go over existing 2x10 or 2x12 cabs.  I'm using the S6688 schematic by our own sluckey (thanks).  They layout will be more in the Fender-style using a laser-cut aluminum chassis -- never been comfortable with separate chassis and a high-voltage supply cord between them.  Garolite and solder-lugs.

Got a couple questions though.  The first is that schematic shows 640 VCT.  The one I've attached shows 680 (I think).  The ClassicTone Supro power transformer comes in at 700 VCT and only 125 ma.  It seems like a beefy unit but I thought I'd better check.  I've got 122 VAC coming out of the wall compared to 110 back in the day.  There are lots of 650 VCT trannies out there.  Since I won't create the DXF file for the chassis until I have the components, I thought I'd see if a stock Fender transformer might be a better idea.

The other question is the filtering.  I got 20/10/10 on the rail.  That's fine.  Just thought I'd see if anyone has stiffened that or it is better to leave the antique charm.

Attached (I hope) is a schematic of the Airline GVC 9010A which is supposed to be the same as the 1688TN except spec-ed for 7027 tubes.  It is hard to read but so far it is dead on.  Thought I'd throw it in for the archives since I  hadn't seen it before.  You can find it with more instructions and gut-shots on Reverb.

Thanks for looking and thanks for the body of work already done on this interesting amp.  Be safe and Happy Thanksgiving, Skip

[scstill]

Been thinking of scratch building a supro as well.
But leaning toward the 15" models

Either the 1696 (alnico speaker with PS in the bottom and preamp in top) or
the 6420 (ceramic speaker with entire amp in the bottom)
Thinking they will be great for guitar;

Anyone have any suggestions or recommendations?
Any thoughts about how the circuits will sound?

[sluckey]

I'm using the S6688 schematic by our own sluckey (thanks).

I don't recall doing a S6688 schematic.

[luthierwnc]

My error.  I have your S6424 on the brain.  sh

[scstill]

does anyone have or know where to get the 1696TN schematic?

[sluckey]

Less than 5 minutes on Google...

     https://www.schematicsunlimited.com/s/supro/supro-1696tn-amplifier-schematic

[scstill]

Less than 5 minutes on Google...

     https://www.schematicsunlimited.com/s/supro/supro-1696tn-amplifier-schematic

Thanks.  I did see this one. But being hand-drawn, wasn't sure if I should commit to it.
Seems that there are no existing manufacturer or engineering drawings left anymore.

[tubenit]

https://www.thegearpage.net/board/index.php?threads/new-build-supro-1688tn-video-added-in-post-32.1245510/

Interesting reading about Leon C.'s project on the 1688TN.   Worth the few pages of reading before building one of them.

[scstill]

https://www.thegearpage.net/board/index.php?threads/new-build-supro-1688tn-video-added-in-post-32.1245510/

Interesting reading about Leon C.'s project on the 1688TN.   Worth the few pages of reading before building one of them.

Agree...
I reached out to Leon and he sent me his 1696 schematic
Hand drawn of coarse :-)

[luthierwnc]

Bookmarked it when I first looked at this build.  I figure I have to work to the 380VDC on the plates.  Allowing for modern wall voltage it seems any of several Fender-style PTs gets me in the ballpark.
I took some time trying to compare the schematic I attached to my reference S6688 schematic and there are a few differences.  It looks like they forgot the 100k grid-leak on the normal input.  Some caps are different but overall it is pretty close.  I'm still wrestling with the filter caps.  The Airline schemo using a 5U4 rectifier tube shows the first node with what seems to start with a '1'.  Might be 16uf since that was a common size.  The second node at the screens is in parallel -- maybe a 10uf and 20uf?
There are two dozen pictures with that Reverb listing

https://reverb.com/item/14015328-1961-tweed-airline-gvc-9010a-supro-1688tn-high-power-dual-tone-thunderbolt
including some pretty good gut shots.  Definitely part of the ongoing archive of that build.  I probably ought to just buy it.  Cheers, sh

[scstill]

.  ...I probably ought to just buy it.  Cheers, sh

nope - build it
are you going to go with vintage or modern speakers?

[luthierwnc]

scstill; not sure.  I've got a pair of Celestion Greenback 10's like leonc but might go with P12N's.  I've already got one.  Course, that's what makes buying an existing amp attractive since most of them have a pair of P12N's which are a third of the total price if purchased separately.  My 2x12 is an open-back with a Celestion G12-65 and a Scumback heavy-magnet H55 cone -- very versatile.  That way I could just make a head.  sh