Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Twist, Don't Shout! Making twisted-pair leads for the Dyna PAS

Moving forward in small leaps and bounds now.

In an effort to reduce hum, I'm using shielded cable in a few select places.  As one example, this is the wiring from the tape monitor switch to the Blend Switch, and then from the Blend Switch down to the inputs on PC-5.  On a stock PAS preamp, this would be unshielded, so I thought this might be a good place to use coax.  The Dynaco manual even indicates that the wiring should be dressed to the front panel as closely as possible, so clearly they were trying to minimize hum.   It's just good wiring practice; this technique was advocated back to the early days of amateur radio.

You can also see the back side (backside?) of our new Alps Blue Velvet pot.

On the coax from the volume pot, I used the PC-5 ends to ground the shield.  The 'hot' wire goes to terminal 9 here, and since terminal 8 goes to ground, and I won't have any other connections there, I'm using it to run the shield to ground there rather than try to find a ground up near the volume control.

I used this really semi-awful Radio Shack stuff I had around.  I tried to be neat, but the outer jacket melts if you look at it for too long.  Yuck.


Now on to something I have a lot of fun working on.

There are fairly long runs of wire from the input board connectors to the selector switch, which means there is a big potential to pick up hum and other noise (RF) there.  Dynaco didn't use any kind of shield at all on this wiring, but I think it needs it.  I would guess Dynaco didn't bother because they were being cheap...meaning they could save money on wire.

Bill Thomas, who I referenced before, went so far in one of his builds as to use coax.  I considered that, but to be honest, I've already spent a bunch of money, the only small coax I have is this Radio Shack junk and I just don't want to spend more for better cable.  So there!

I'm going to install the PAS selector switch kit I got from Cucio Audio Engineering, which comes with enough wire to wire the inputs as twisted pairs, with one lead acting as a shield, so I just figured I'd stick with that.   This method actually goes back to the earliest days of radio. 

Anyway, back to where I started.  We need to make up two lengths of twisted pairs.  Curcio gives you teflon-insulated, silver-plated copper wire for this, a length of black, and lengths of green and red.  I cut an 8 foot section of red and black and put one end in a vise.

Then I took the other ends and put them in my handy-dandy trusty English-made Stanley hand drill (aka Eggbeater).  Chuck 'em in there.

Then you just string the whole length out, put a little tension on it, and turn the drill clockwise.

I have tried a power drill for this, but it goes way too fast for my liking.  The hand drill is much more controllable.

This is what the end product looks like - about seven and half feet of nicely twisted wire.

Repeat with the black and green and you're ready to start wiring.

 
 
 
 

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