Another question - Shielding the PI output ?

[pedro]

Is it worth using shielded on the PI output to power tube grids ?

At m0menet in the old donor PA chassis ( repeating myself ! ) I have to have a 7" run from PI board to grids of power tubes - so I shielded them.

Now wondering whether I'd get even better top end and no issues if I just use plain wire ?

Rgds
Pete

[novosibir]

Is it worth using shielded on the PI output to power tube grids ?

Actually not necessary! But remember some rules of proper PA design:

- twist the grid wires
- the swamp resistor has to be on the tube socket
- stay away with the grid wires from the OT's wires & the NFB wire as far as possible
- twist the OT's primaries w/o the CT wire included
- twist the OT's secondaries with the common wire included
- always ground the OT's secondary common to the speaker jack
- if you have insulated speaker jacks (always better), ground it to the PI's ground

Larry

[dogears]

Why twist the wires that are out of phase with one another?

Is it worth using shielded on the PI output to power tube grids ?

Actually not necessary! But remember some rules of proper PA design:

- twist the OT's primaries w/o the CT wire included

Larry

[novosibir]

Why twist the wires that are out of phase with one another?

In case of the grid wires to the output tubes, to cancel out to each other possibly catched stray fields from other 'transmitter' sources, especially the OT wires - similar as a humbucker PU is operating.

In case of the OT wires, to minimize their electromagnetic stray field around the wires - a similar effect as at the twisted heater wires.

Larry

[heisthl]

The only time I have ever sheilded the PI grids wires was on this project:
http://ampgarage.com/forum/download/file.php?id=1803
because the PI tube was in between the output tubes. It did not seem to hurt the sound quality but sure made this amp quieter.

[Darkbluemurder]

Is it worth using shielded on the PI output to power tube grids ?

Actually not necessary! But remember some rules of proper PA design:

- twist the OT's primaries w/o the CT wire included


Larry

It is really important NOT to include the CT wire in the twist. I did this once with a Marshall which screwed up the tone big time. Took out all of the harmonics and gave a nasal midrange honk which made the amp sound the same regardless of what guitar I played through it. Thanks for helping me out on this, Larry.

[novosibir]

Thanks for helping me out on this, Larry.

Anytime

You probably have read my advice concerning this on the Metroboard?

Larry

[Darkbluemurder]

Thanks for helping me out on this, Larry.

Anytime

You probably have read my advice concerning this on the Metroboard?

Larry

Of course I did, it was me who started the thread there!

Cheers Stephan

[Funkalicousgroove]

what purpose does twisting the OT primaries serve? I have never seen this before.

[Bob-I]

what purpose does twisting the OT primaries serve? I have never seen this before.

Actually one of my Peavey transplants had the OT wires twisted. It sounded a bit dull until I untwisted them. It was a noticable difference.

[skyboltone]

what purpose does twisting the OT primaries serve? I have never seen this before.

Here's' Francesca. Two whole turns......

[IMG:800:600]http://i20.tinypic.com/1tn6ec.jpg[/img]