Phase Linear 700 B amp - any cautions before I power it up?

[bmwr75]

Hey Guys,


Bought this at a flea market today for not a lot of money. The seller was not present, but had a tag on it stating one channel is not working, but the transformer is good. Of course I'm hoping it is just a dirty gain pot or dirty coupling selector switch (normal vs. direct, whatever that means) on the rear.....fingers crossed.

I've never worked on any Phase Linear equipment. Any common failure modes I should be looking for in this amp? Any reason I can't just go ahead and hook it up to some speakers and a source and give it a go?

[bmwr75]

I just checked the DC offset. Got 125 mV on the right side, -1 mV on the left.

Right side has a problem. Ideas on what to do next?

Must have not been powered up in a while. The work bench lights dimmed when I turned it on and those huge power supply caps starting charging up.  Didn't happen the second power on cycle to check the other side.

[bmwr75]

Isn't this a Bob Carver amp?  Isn't this a Carver centric forum?  .........  crickets chirping.

Come on guys, speak up.

[Kingman]

Got alot of Phase Linear amps....refer back to the Pittsburgh experts. They have my 700 series 2 now.....

[OldiesButGoodies]

This is a brand-diverse forum with a special level of endearment w Carver crap.   Anders or Tom should weigh in as the senseis of Carverdom.

[bearjew]

Resistors are probably bad on that channel. Someone probably drove low impedance speakers with it, which will make the resistors catch fire: hence "flame linear". Not too hard of a fix. Bring it to the shop some time, we could definitely do it.

[bmwr75]

You work at the shop @bearjew?

[OCCD]

You work at the shop @bearjew?

I traded PBJ a ReVox B77 for bearjew.  Dam he eats alot.

[papabearjew]

He shits a lot too

[bearjew]

This is true. My dad enjoys the b77, and I work at the shop haha. And yes, I do shit a lot.

[BrianT]

Dam he eats alot.

At Carverfest 13, he only had one meal a day, he started it as soon has he got up
and stopped eating when he passed out at night due to the alcohol taking over.

Brian

[bearjew]

Dam he eats alot.

At Carverfest 13, he only had one meal a day, he started it as soon has he got up
and stopped eating when he passed out at night due to the alcohol taking over.

Brian

This is something I take pride in.  I gained 20 pounds that week I think.  Took me 3 weeks to deflate.

[Kingman]

Speaking of amp repair.....

[bmwr75]

Have started studying the troubleshooting steps in the service manual.

Disconnected the power supply filter caps and tested them both for shorts. They are not shorted.

Start testing the banks of output and driver transistors per the service manual.  Looks like I've got some blown outputs in the left channel.

Can I replace just the blown outputs, or do I have to replace all of the ones in that channel?  What is the modern day replacement equivalent?

Left bank - top to bottom - BOLD = suspect
0.6 ohm
0.3
0.6
0.2
0.3
185.0 <- the driver

Left middle
0.4
0.45
0.6
0.2
0.6

Right middle
12.3
12.2
12.2
12.1
12.1
184.5

Right
12.0
12.0
12.0
11.9
12.0
185.3

[bearjew]

when you replace output transistors, i believe you want to change them all