Phase Linear 2000 troubleshooting

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gadget73

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#162
Do these things have a "death cap" that ties one side of the power line to chassis for a pseudo-ground reference? I wonder if that might be causing hum if that is the same place the RCA jacks ground to. I dont know if they were still doing that stuff by the 70s, but it was very common in the tube era.
 
Gepetto

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#163
gadget73 said:
Do these things have a "death cap" that ties one side of the power line to chassis for a pseudo-ground reference? I wonder if that might be causing hum if that is the same place the RCA jacks ground to. I dont know if they were still doing that stuff by the 70s, but it was very common in the tube era.
Click to expand...
Does not
 
Coldsmoke

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Well,

I replaced all the caps by the original values, threw in the new transistor, checked the continuity of all the tracks, made sure that the bolts to the chassis were tighten.
I scoped the equipement and it appears that :

The 50Hz hum is still here (as light as it it is...)
REAR OUTPUT doesn't work (it wasn't working before).
FRONT OUTPUT works well for both hi and low level inputs

Strange thing : the preamp sends a 50Hz signal to the output when it's off. I noticed it when I heard a sound through my speakers while it was off. I scoped it and it is a 50Hz signal....
 
Gepetto

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Coldsmoke said:
Well,

I replaced all the caps by the original values, threw in the new transistor, checked the continuity of all the tracks, made sure that the bolts to the chassis were tighten.
I scoped the equipement and it appears that :

The 50Hz hum is still here (as light as it it is...)
REAR OUTPUT doesn't work (it wasn't working before).
FRONT OUTPUT works well for both hi and low level inputs

Strange thing : the preamp sends a 50Hz signal to the output when it's off. I noticed it when I heard a sound through my speakers while it was off. I scoped it and it is a 50Hz signal....
Click to expand...
Take R68 (33K) and C39 (0.0027uF) off the AC power switch and see if that gets rid of it. It has in the past.
 
Gepetto

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Coldsmoke said:
Well,

I replaced all the caps by the original values, threw in the new transistor, checked the continuity of all the tracks, made sure that the bolts to the chassis were tighten.
I scoped the equipement and it appears that :

The 50Hz hum is still here (as light as it it is...)
REAR OUTPUT doesn't work (it wasn't working before).
FRONT OUTPUT works well for both hi and low level inputs

Strange thing : the preamp sends a 50Hz signal to the output when it's off. I noticed it when I heard a sound through my speakers while it was off. I scoped it and it is a 50Hz signal....
Click to expand...
Do you know why the rear outputs are not working?
 
Coldsmoke

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Gepetto said:
Take R68 (33K) and C39 (0.0027uF) off the AC power switch and see if that gets rid of it. It has in the past.
Click to expand...
R68 is removed, C39 is on it and the .01uF 1kV is removed. I'll give a try to the removal of C39.

Concerning the rear outputs I just checked the 4739 in the ambience circuits by scoping it through the socket I installed and it appears to be faulty.

Man! 3 out of 4 of these IC's are burnt! I only have one out of the two that Lee kindly sent me on that's working....
 
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laatsch55

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The ones I sent I pulled from an old one I had laying around. I thought I had some spares but they turned out to be 4136's. I do have some more I could pull if need be....
 
Coldsmoke

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laatsch55 said:
The ones I sent I pulled from an old one I had laying around. I thought I had some spares but they turned out to be 4136's. I do have some more I could pull if need be....
Click to expand...
It's very kind of you Lee, but, as you know, I found a NOS here, I think I'll go for new ones.
I hope this preamp deserves all this sweat :toothy5:
 
OneTonScoutII

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laatsch55 said:
The 4739's are a very weird duck. I have tried quite a few in it's place and they always oscillate. Joe tells me it has something to do with bandwidth and phase angles. We were going to rework the circuit on a 2000 to accept a different op-amp one of these days but so far have not done it...
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Yes Please!:toothy5:
 
laatsch55

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Life is pretty tough in the oilfield right now and haven't had the time....someday...
 
OneTonScoutII

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laatsch55 said:
Life is pretty tough in the oilfield right now and haven't had the time....someday...
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While reading about the op amps, I read that improving the power supply would do a lot to improve sound. What are your thoughts on this? What would one use as an upgraded power supply?
Thanks
 
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