Any problem with serial wiring of heaters?

[Jim R.]

I'd like to wire the filaments of my s.e.x. amp such that there is only one pair of leads coming from the C terminal strip, and then daisy chain the second tube off the first.  Is there any problem that I'm not considering when doing this?  I will keep the shield intact from the first tube to the second, and the wire will be heavier gauge to handle the additional current.

Thanks,

Jim

[Paul Birkeland]

This shouldn't be the end of the world.  The stock shielded twisted pair will work fine in terms of current.  Just run the first run from the filament DC supply to one tube, connecting the shield at the lower hole of the center terminal on the closest 5 lug terminal strip.  Run the second run to the other tube, connecting the shield at that tube's closest 5-lug terminal strip.

If you get tempted to use heavier gauge wire, you may end up with shielded twisted pair that is stranded, and that can make a huge mess in a hurry. 

-Paul

[Jim R.]

Hi Paul,

I'm actually making my own STP out of solid core wire because the STP with the kits now is stranded.  Besides, I seem to have misplaced my original package of wire, but have plenty of other suitable wire on hand.

Thanks for theadvice on grounding points too.

-- Jim

[Paul Joppa]

The shield should be grounded only once. It is grounded at C1, and should NOT be grounded by the middle terminal of any other terminal strip. To maintain a daisy-chain shield, the shields of the two segments should be soldered to each other and insulated from the chassis plate and other adjacent wires. IIRC, there are no unused non-grounded solder terminals nearby to use for this.

The purpose of this it to prevent formation of ground loop currents, adjacent to the magnetic field of the power transformer.

[Paul Birkeland]

So they cannot be wired as the shields are done in the Seduction, Foreplay III, Repro Amp, or Eros?

[Paul Joppa]

So they cannot be wired as the shields are done in the Seduction, Foreplay III, Repro Amp, or Eros?

Those are all wired so that the shield is grounded at only one point, as I said.

Now that I think a little more, yes you could chassis-ground the shield at the first tube socket, removing the ground at the power supply end. Then the section to the second socket would have its shield grounded at the same point with no shield wire at the second socket.

[Paul Birkeland]

Those have the shields grounded to multiple points on the chassis.  The seduction uses the fewest (2), while the Repro 5 separate heater shield ground connections to the chassis...  I'm not seeing the difference between these two and the proposed heater wiring for this particular SEX amp.

[Jim R.]

It's good to know that any of these schemes will work.  My preference is to keep things to as few grounding points as possible and it's really quite easy for me to wire it grounded at the original terminal strip and then to the main grounding lug next to the IEC inlet, and then just tie the shields of the two sections together, making sure that it doesn't contact the plate or another ground point anywhere else.

Thanks for all the thoughts.


-- Jim