Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

[laatsch55]

Good man, glad to seee you doing your part!!


I use crude oil condensate to clean the heatsinks, took all of 3 minutes. Don't know what's in the stuff but as soon as it makes contact the dreaded white grease is on the run. To give you an idea of it's vbapor presure, when it's 80 degrees outside, you can watch it evaporate/.

 

[NavLinear]

Good man, glad to seee you doing your part!!


I use crude oil condensate to clean the heatsinks, took all of 3 minutes. Don't know what's in the stuff but as soon as it makes contact the dreaded white grease is on the run. To give you an idea of it's vbapor presure, when it's 80 degrees outside, you can watch it evaporate/.

That damn monkey cum is tough to get off - no finger flicking will help and do not get on your clothes! The wife will kick your ass!

 

[NavLinear]

Three nights a ago Cathy started getting severe distortion on the left channel. I have chased it all over the board for the last 3 nights and am no closer to finding it than I was when I started. there were numerous slips of the probe this time too, so many I do not trust the reliability of the SECOND board. Thus, the THIRD board was just finished. It's a beauty. Don't know what it is about this particular amp, but it took 3 boards last time too.


Cathy will now get the outputs stripped, heatsinks cleaned, sockets lifted and inspected too make sure there are no whiskers, or cut off leads that will short things out after a hard ride back to Scott. New grease and new mica insulators too. Gonna give it every chance in the world. The only thing it won't get is that HARD WEEK of testing that goes on here. Promised this to be shipped by tomorrow morning. Jani's got my favorite coffee going. We're going in

Damn dude - you need a board level test set up big time!

 

[laatsch55]

You can actually get 2-3" inches of clearance by taking the 3 tab terminal strip loose and letting it float with the sockets...

Kinda groody in there too, may take the condensate to that....

 

[laatsch55]

Damn dude - you need a board level test set up big time!

Dennis ---ain't no doubt about that.

 

[laatsch55]

Sockets reseated, new bias tranny's in, there was a lot of stuff under the sockets, enough to have caused what I thought it might. Now the outputs...

 

[laatsch55]

Bias tranny's. Acetone is great for getting scorch marks off of wire, sockets, solder, etc....
Bias tanny brackets courtesy of ----NavLinear--- FabroNav-------

 

[laatsch55]

Outputs in, board next....

 

[laatsch55]

Still not getting enough bias voltage on the left channel-------Joe??

 

[Gepetto]

When set at max pot setting Lee, what is the DVM reading with your DVM plus lead on the C-L pad and your minus DVM lead on the E-L pad? That will tell us if it is the bias circuit not performing properly or downstream from it.

 

[laatsch55]

Hang on, I know at max setting It goes to 16 volts DC on the speaker output, at minimum .004 offset. Just a minute there Joe...

 

[laatsch55]

Collector pad-----+1.3 volts DC, Emitter pad---MINUS 1.001 volts DC.

 

[Gepetto]

Lee
Your bias setting should have negligible effect on output offset.

 

[laatsch55]

Max setting---25 volts DC, collector pad, emitter pad--Plus 15 and dropping steadily, both of them dropping steadfily.

 

[laatsch55]

Max setting---25 volts DC, collector pad, emitter pad--Plus 15 and dropping steadily, both of them dropping steadfily.

 

[laatsch55]

Lee
Your bias setting should have negligible effect on output offset.

First one I've seen do it.

 

[Gepetto]

Hi Lee
You have something very strange going on in that chassis, sure you know that by now

SPICE model results for you on the bias circuit

With pot set at min (full CCW)
C = 1.37V
E = -0.886V

With pot set at max (full CW)
C = 1.75V
E = -0.958V

Again this setting should not have any effect output offset. Your amp is acting like you have some or all blown emitter resistors in the lower half of the output stage if you cannot achieve a high enough bias setting. Check those resistors and solder joints. Does every emitter of every transistor in the negative half of the left output stack have approximately -100V on it? Probe carefully, don't want additional damage.

 

[laatsch55]

Yes, minus 106.8 to inus 107.

 

[Gepetto]

You seem to be chasing the same problem as you had with the last board. No apparent negative half of the output stage on the left channel

Can you post a closeup of the positive and negative stack wiring for the left channel. My suspicions are there.

 

[laatsch55]

Yes sir, I can.