revamped S.E.X. C4S upgrade

[Doc B.]

We used to sell the C4S upgrade for the S.E.X. kit as a part of a package that included caps, and had instructions for installing the MQ iron upgrade. A link to those instructions are on a sticky in this forum. Over time we split the iron from the C4S kit and the caps became unavailable. Recently we have had several requests for S.E.X. C4S upgrade by itself and I decided it was time to update the kit to more up to date PC boards. And so we are now selling a slightly improved C4S kit for S.E.X. kit that will install a bit more securely.

http://www.bottlehead.com/store.php?crn=44&rn=448&action=show_detail

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.bottlehead.com%2Fsc_images%2Fproducts%2F448_image.jpg&hash=e06661a74f38c5eca03891ccd730b336b41c8b6b)

[Grainger49]

Excellent, another use for the "Universal board."  That is ingenious!

[JC]

Cool!  Out of curiosity, what does it mount to?

[Dr. Toobz]

Am I correct in that the boards are a new thing, but the actual circuit is otherwise the same (i.e., there would be no benefit to ripping out the old boards to put in these new ones, other than for aesthetics?)

[Doc B.]

The boards mount onto the forward socket mounting screws, on top of 1" nylon standoffs. The circuit is the same as the original S.E.X. C4S. We have updated to the MJE5731A as well, as it has proven to be more robust than the MJE350 in applications where the underchassis environment can get pretty warm.

[corndog71]

Only $45 to make my Sex amp even better?!

This is good news!

[bainjs]

Are the caps included now? If not, what value do we need to look for?

Thanks

[JC]

If you a referring to the C4S kit, I believe that you will find that all of the parts to complete the C4S will be included.  I don't believe that there are any caps involved.

The old iron upgrade used to include changing the interstage and parafeed caps along with plate chokes and output transformers, as well as the C4S.  You can still do the whole thing, but Bottlehead just sells the C4S now.

IIRC, the value of the interstage coupling cap remains the same as what came in the SEX; you just replace it with your favorite high-end equivalent.  The value of the parafeed cap depends on whether you upgrade the iron.  If you just want to upgrade the cap alone, you use the same value as came with the SEX.

[kgoss]

The cap values are in the old C4S instructions.  The text below is a cut/paste from those instructions.  If you are going to add the Magnequest iron later you can go ahead and install the 2uF capacitor of your choice rather than upgrading the 1.0uF coupling capacitor only to replace it with a 2uF capacitor later when you do install the iron upgrade.  I believe Paul posted that it is OK to replace the 1.0uF with a 2.0uF even before you add the C4S upgrade or the iron upgrade.  But of course Paul will have to confirm that.

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You will also need to supply two of your favorite flavor of coupling capacitor with the following ratings

2uF, rated for at least 600VDC

Optional - you may also wish to upgrade the two stock 0.1uF interstage coupling capacitors with a boutique capacitor of the same 0.1uF value and 600VDC rating, as shown in the instructions below.
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[Paul Joppa]

...I believe Paul posted that it is OK to replace the 1.0uF with a 2.0uF even before you add the C4S upgrade or the iron upgrade.  But of course Paul will have to confirm that. ...

Confirmed.  :^)  I love this forum, usually somebody posts an answer before I even see the question, and usually it's right.

Just another option - you can leave the 1uF cap, it will work well with the MQ upgrade. Bass won't go quite as deep but it will be more solid, in the sense that the tube is working onto a more comfortable load so the deepest bass power handling is improved. The difference is subtle.

You can also bypass the stock 1uF with another cap of 1uF to get 2uF total if you have the iron upgrade. Might make for some interesting experimentation, and a reduced cost.