Larry's Phase Linear 700B

[laatsch55]

Late last night i did pull one end of R75, and R76. i was trying to isolate Q10 and 7 from the equation. I don't know if it told me everything I was lookin for though. The protection circuit was no longer flooded with -100 volts DC. The regulated low voltage section is not affected, it's doing fine. My trouble is trying to connect where the -100 is getting from the rail at. Could be a very convoluted route.

 

[Gepetto]

Hi Lee
Quick question, the other night you said you had +100V at the collector of Q4 which is not right at all. Your latest post here says -100V which is what the collector of Q4 should be operating at. It is a current source that does the level shift in order to drive Q5. If it is indeed -100V at the collector of Q4, I would look elsewhere in the circuit. What kind of output offset are you getting with no input signal and no output load?

 

[jbeckva]

Hi Lee,

I'm going to dive in here too a lil' bit as I've done some "trons" too in a past life...

Now... hmmmm.. jump in here if I'm mistaken after reading this through a little...

You say you have -100 all around Q5, right? Still?

Now I am just putting this one out there, but ... if by chance back a few posts ago when you swapped both Q5 and Q7, could it be possible to have swapped them accidentially - physically? My reasoning is this - if Q7 which calls for a PNP has an NPN in it's place, then the negative rail through the negative output array would go right through over to Q5's collector, since Q7 collector through Q7's base would be a straight forward biased diode. It would come in on 3L, straight through Q7 and R76.

(I'm seeing how crusty I still am after 14 years heheh)

 

[laatsch55]

Hi Lee
Quick question, the other night you said you had +100V at the collector of Q4 which is not right at all. Your latest post here says -100V which is what the collector of Q4 should be operating at. It is a current source that does the level shift in order to drive Q5. If it is indeed -100V at the collector of Q4, I would look elsewhere in the circuit. What kind of output offset are you getting with no input signal and no output load?

Minus rail voltage Joe. I have +100 on the collector of Q5, -100 on the base of Q5, and -100 on the emitter of Q5.

 

[laatsch55]

Hi Lee,

I'm going to dive in here too a lil' bit as I've done some "trons" too in a past life...

Now... hmmmm.. jump in here if I'm mistaken after reading this through a little...

You say you have -100 all around Q5, right? Still?

Now I am just putting this one out there, but ... if by chance back a few posts ago when you swapped both Q5 and Q7, could it be possible to have swapped them accidentially - physically? My reasoning is this - if Q7 which calls for a PNP has an NPN in it's place, then the negative rail through the negative output array would go right through over to Q5's collector, since Q7 collector through Q7's base would be a straight forward biased diode. It would come in on 3L, straight through Q7 and R76.

(I'm seeing how crusty I still am after 14 years heheh)

Just checkred Jer, they are correct.

 

[jbeckva]

Pull Q7.. whatcho got then on Q5?

 

[laatsch55]

The same as posted above Jer.

 

[laatsch55]

MeasuringQ7's pads with it out, minus rail on the collector plus rail on the emitter and base.

 

[laatsch55]

We now have positive rail voltage on the output.

 

[laatsch55]

In the past when I've had rail voltage on the output AND IT DIDN'T blow fuses it was in the front end.

 

[jbeckva]

Hmmm, that's a tough nut there

 

[laatsch55]

Ya think?? Time to rig up a board tester. Should have done it long ago. I need to eliminate the chassis as a source of problems, then you can concentrate on the board.

 

[Gibsonian]

Would be nice for you to have a board tester and a chassis tester. That'd be a timesaver for you in the long run.

 

[laatsch55]

Yes Scott, knowin me like we know me, it really would. seems like I have to have a disaster on each piece of test equipment before I make no more mistakes with it. The AP is not that hard to go from times 1 to times 10 on the generators and that's basically what I did. the amp will be better for it. The improved grounding and a couple other little things while I'm in there, bypassing the BR, New 35 amp Br, hash caps on the output rows........ things I didn't do cause Larrt liked the sound, so I wasn't going to change anymore than I needed too.

 

[laatsch55]

Doug, the new board is done and will be installed tonight after work.

 

[fitz43]

Great! thanks.

 

[Gibsonian]

Yes Scott, knowin me like we know me, it really would. seems like I have to have a disaster on each piece of test equipment before I make no more mistakes with it. The AP is not that hard to go from times 1 to times 10 on the generators and that's basically what I did. the amp will be better for it. The improved grounding and a couple other little things while I'm in there, bypassing the BR, New 35 amp Br, hash caps on the output rows........ things I didn't do cause Larrt liked the sound, so I wasn't going to change anymore than I needed too.

You know these amps as well as anyone. I'm just thinking of an easy button for ya.

 

[laatsch55]

Scott, thanks, I have my days.......

 

[laatsch55]

Right channel done. We'll be testing in about 30 minutes.

 

[laatsch55]

Left side done.