New guy with a new ST-70 project

[Wardsweb]

Hello all - some of you may already know me and others may have seen me around the internet. I just found out about this place yesterday when talking with a buddy about my new project. I'm taking a stock ST-70, upgrading it and putting it on a new custom chassis. I've already orderd Shannon's driver board and will order a new power transformer sometime next week.

Here are a couple of pictures of the unit I'm starting with.

[Wardsweb]

What I envision is something along the lines of this battery powered preamp I just built. Think of the this wood cabinet expanded to fit a flat plate of aluminum with a 90 degree bend down at the back. It slides into the cabinet from the back. I do a layout similiar to the ST-70 and put all the connectors on the back.

[TerrySmith]

Looks like an insteresting project! I wish I had a good woodworking imagination, anything I do with wood looks like Homer Simpsons spice rack!

Whats your plans for the old chassis and transformer?

[Wardsweb]

The process has begun. I started to layout the new chassis on some .080 aluminum while I wait on a lot of new parts to come in. One of which (Shannon's driver board) I need as a template to cut the tube holes. I plan on mounting the parts on the underside of the board and the sockets on top, so I can mount the entire assembly under the chassis with only the tubes sticking out.

[EWBrown]

Hi Luther,

Welcome aboard! Looks like a nice project! I recently built up one of Shannon's ST70 boards as you described, (for a long-delayed EL84 PP project, built up on a salvaged Heath AA-151 carcass), with everything but the tube sockets under the PC board, so only the three tubes will see daylight. The PSU and output section is already built up,

I just have to drill four holes, punch three more, and do some wiring, and it should be good to go...

You may want to consider adding a crosswise length of 1/2 or 3/4 inch aluminum angle bracket under the chassis to act as a "stiffener" if the heavy iron makes the top plate sag - those trannies are HEAVY... The 0.080 aluminum may be thick enough so this won't be necessary.

/ed B in NC (AKA Dyna Saur on the Bottlehead forum).

[Wardsweb]

[quote="EWBrown"]
You may want to consider adding a crosswise length of 1/2 or 3/4 inch aluminum angle bracket under the chassis to act as a "stiffener" if the heavy iron makes the top plate sag - those trannies are HEAVY... The 0.080 aluminum may be thick enough so this won't be necessary.
quote]

The 90 degree bend down at the back acts as a stiffener across the back where the trannys are. Most likely with that in place I could have gone with a thinner piece of aluminum but I've always been about over doing.

[Wardsweb]

I've started a page on the build, just in case anyone wants to follow along or duplicate it in the future.

http://wardsweb.org/audio/ST70/

[Wardsweb]

The latest picture gives a better idea of what the final product will look like. I have the quad of Shanling EL34 and a matched quad of Ruby EL34 to try.

[Sal Brisindi]

Nice job on the rebuild. Looking at the website you created, you mention using 500V electrolytic capacitors in the power supply, I would up that to 525v minimum as the 500v can be exceeded at power up until the EL34's start pulling their full current.

Regards,
Sal

[Wardsweb]

Shannon's driver board is built to fit my custom chassis.



Most all parts are on the bottom side.



Only the sockets and pots are on the top. I took a lot of time to get the sockets soldered in at the same height as the pots.



It came out perfect. It did take a lot of time and measuring to get the holes in just the right places.

[Geek]

Cool PCB colour, Shannon!

Cheers!

[TomMcNally]

Looks sweet !

Tip: Mark the 4 corner holes of the UNBUILT board
and drill 4 holes in your chassis. Bolt the board in place.
Mark and drill the small pilot holes in the center of the
tube sockets and pots and cut your full size holes. Perfect!

Clever man that Shannon Parks ... his idea has been
used by some others since, but I think he was the first
to use that feature.

[Sal Brisindi]

I like the 2 small holes for the bias balance pot on top of the chassis. Looking good! I'm looking forward to the rest of the build.

Sal

[Wardsweb]

Looks sweet !

Tip: Mark the 4 corner holes of the UNBUILT board
and drill 4 holes in your chassis. Bolt the board in place.
Mark and drill the small pilot holes in the center of the
tube sockets and pots and cut your full size holes. Perfect!

Clever man that Shannon Parks ... his idea has been
used by some others since, but I think he was the first
to use that feature.

Yes that is what I did for the tube sockets but the bias pot adjustment screw took some doing. There isn't any margin for error. I ended up drilling a hole in the board where the adjustment screw was and using that as my guide for drilling the chassis.

[skidave]

Hi Wardsweb! I remember you from the SAE / GAS chat group on Yahoo. I'm not sure if that is still around? I have not logged in for years. As I recall, you have a large SAE collection. (I have four Ampzillas and a few other GAS items. I would love to find a SAE2600 sometime for a reasonable price.)

Good luck with your project. This forum is great for help and suggestions.

Dave