Larry's Phase Linear 700B

[NavLinear]

Back from the horses - must've missed the fun. So Q1 was shorted and loading the AP? Out of curiousity what did you do to isolate the problem?

So you're seeing 60 Hz at the output now?

 

[laatsch55]

Q1 didn't check right in circuit so I pulled it. That was 2 nights ago, then fired it up without Q1 in circuit which smoked R51 in the LED board. Put a new Q1 in and everything is fine, except for the hum of course. It sounds fantastic other than the hum. It's not volume linked and looking at the backwall there is AC going to the thermodiscs that is rubbing against the collector bus bar and parallel with some other DC runs. A relocation of te AC in is in order and a rebundling of wiring in general, along with a BABB and several other things while I'm in there that deep.

 

[laatsch55]

ok Joe, when rebundling the wires, do I have to twist the hi voltage DC or is there anothert way to cancel the effects? As far as the AC goes , all that will be routed around the top away from everything, except the ground return from the RCA in's ground plane. Do I need to reroute the rca ground?

 

[laatsch55]

And, I've aslways thought having a ground tab an 1/8 inch away from the rails wads a noise maker too, as in the center of the 3 tab terminal strips on the back wall.

 

[mlucitt]

Ground should be the absence of all hum. I don't think the terminal strip caused any issues with the DC. Hum is from the AC wires such as the thermostatic switch and the power switch wiring. I try to keep those from everything else.

 

[laatsch55]

Yep, that's the goal of the latest "going in". Now the AC switch is bundled in with the low signal wiring going to the light board, I'm thinking of a way to keep those outta there and short of installing the On/Off switch last and first everytime you take the faceplate off, a harness plug of some sort.

Pics, caps out, BR and buss bar out, fuse holder out, wire unbundled. And that mess under the right output rail.
It will get a new 35 amp BR, properly bypassed, a new BABB( Bad Ass Bus Bar) and god knows what else.

 

[mlucitt]

Nice detour on the way to a minor hum job.

 

[laatsch55]

Well, ya know I can't ust get rid of the hum, gotta do other stuff while I'm there.

 

[NavLinear]

A link to "Twisted Pair Cable Noise"

http://www.wisc-online.com/objects/ViewObject.aspx?ID=CIS5108

We use shielded twisted pair cabling in most of our harnessing - I've been bit more than once when we short cut something. I have a care package out your way but I'm starting a new list already.

I knew what a BABB was.

 

[laatsch55]

I knew you knew what a BABB was, that was for those who didn't know. A new list??

 

[laatsch55]

Nice link, it's nice to see it drawn out like that.

 

[laatsch55]

Ok, bought got all the AC wire gutted. An interesting find, the wires going from the thermoswitces and the On/Off switch was some very thinly insulated #16, almost mistook it for #18.

 

[laatsch55]

Gotta cut out for a couple hours, Squidley's 2nd birthday party at the skating rink. Pretty amazing when ya think we didn't think he'd make it to his first one.

 

[jbeckva]

Hey I forget...

is it better to have a wire that could cause interference perpendicular or parallel to the wire to be protected?

 

[mlucitt]

Perpendicular is better if close at all.

 

[laatsch55]

I did remember that, if they have to cross, at right angles.

 

[mlucitt]

Lee, that green wire in picture 1 is kind scraggly. Also, I like those 4004 flyback diodes a little father away from the terminal strip. If they touch ground, it's all over but the tears. I cut the ground wires to the terminal strip middle post too. They do nothing.

Chuck did that one, eh?

 

[laatsch55]

Yep, ol Chuck. Yeah the 4004's arte a little close. they've been manhandled pretty hard the last couple days. That tiny green wire is - ground for the + 24 volt Dc power source for the ampslabs DC protect.

 

[mlucitt]

Sorry, I thought the green wire was attached as shown. Now I see it is only dangling. My glasses are dirty, again. Of course, it goes to the STAR ground, right?

 

[laatsch55]

Yes it does. On my first cup of coffee. When the 2nd one clears the hatch this 700 is going to be done today, or late tonight, whichever occurs first.