549: Difference between revisions

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549 (view source)

Revision as of 23:21, 16 April 2019

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to have linear phase response over this same frequency range.   
to have linear phase response over this same frequency range.   


In the 549, this buffer is implemented as follows:  A [[6DJ8]] tube configured as a
In the 549, this buffer is implemented with a [[6DJ8]] cathode follower at the plug-in interface
cathode follower is used at the interface with the plug-in to present a high impedance
driving an NPN BJT differential amplifier at the bottom of a cascode with a [[7119]] tube on top.   
to the plug-in.  This input stage drives an NPN BJT differential amplifier,
which operates at the bottom of a cascode configuration with a [[7119]] tube on top.   
The output of the cascode (the plate of the 7119) drives the [[delay line]].   
The output of the cascode (the plate of the 7119) drives the [[delay line]].   


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Line input is connected to main transformer primary via two switches, one inside the chassis to select the 110 V or 230 V range, and another on the rear of the chassis to select Low/Medium/High voltage in either range.
Line input is connected to main transformer primary via two switches, one inside the chassis to select the 110 V or 230 V range, and another on the rear of the chassis to select Low/Medium/High voltage in either range.


Multiple secondary windings feeds diodes for rectification for different voltages. Both center-tap and bridge configuration is used.
Multiple secondary windings feeds diodes for rectification for different voltages. Both center-tap and bridge configuration is used. Transistors and/or tubes are used for regulation.  
Transistors and/or tubes are used for regulation.  


As is common in many Tektronix scopes, all regulated voltages are referred to the negative regulated rail (−150 V in this case) by fixed low-tolerance dividers.  Only the −150 V voltage is trimmed, its reference is a [[5651]] VR tube.  A [[12AX7]] is used as the comparator, three [[12B4]] in parallel are used as series pass tubes. A [[6AU6]] is used as an error amplifier.
As is common in many Tektronix scopes, all regulated voltages are referred to the negative regulated rail (−150 V in this case) by fixed low-tolerance dividers.  Only the −150 V voltage is trimmed, its reference is a [[5651]] VR tube.  A [[12AX7]] is used as the comparator, three [[12B4]] in parallel are used as series pass tubes. A [[6AU6]] is used as an error amplifier.
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==Repair issues==
==Repair issues==
The 549 from Portland factory uses ONE black paper-capacitor  from Areovox. Capacitor with 0.5 µF 400 V rating is using in horizontal amplifier. Result: compressing  trace on right side.   
===C335===
Solution:  Replacing him with ordinary 0.47 µF 630V(and above) capacitor.  Their location is upper chassis, middle.
549 scopes from the Portland factory contain one black Areovox 0.5 µF / 400 V capacitor in the horizontal amplifier (in the middle of the upper chassis) which is often deteriorated. When this is the case, the trace is compressed on the right side.  It can be replaced with a modern 0.47 µF / 630 V (or higher) capacitor.  This problem does not appear to occur in Dutch-made 549s.
 
Ironically, dutch made 549 have never this problem.
 


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