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C808 high DF self-heats and causes HV thermal runaway
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(C808 high DF self-heats and causes HV thermal runaway)
 
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|manufacturer=Tektronix  
|manufacturer=Tektronix  
|model=547  
|model=547  
|summary=50 MHz scope
|summary=50 MHz oscilloscope
|image=Tek 547 D-Alt-Trace.jpeg
|image=Tek 547 D-Alt-Trace.jpeg
|caption=Tektronix 547 with [[1A1]] plugin, in ALT Delayed Trigger   
|caption=Tektronix 547 with [[1A1]] plugin, in ALT Delayed Trigger   
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|series=500-series scopes
|series=500-series scopes
|manuals=
|manuals=
* [https://w140.com/mmm/tek-547.pdf Tektronix 547 Manual with 547 Notes (PDF, 128MB)]
* [[Media:070-0398-00.pdf|Tektronix 547/RM547 Manual]] <small>070-0398-00, plus "547 Notes"</small> (OCR)
* [http://bama.edebris.com/download/tek/547/547.djvu Tektronix 547 Manual (DjVu)]
* [[Media:Tek_547_544_546_tech_instr_and_training.pdf|Tektronix 544/546/547 Technical Instruction and Training]] (OCR)
* [https://w140.com/tek_547.pdf Tektronix 547 Manual (PDF, 60MB)]
<!-- * [[Media:Tek 547 544 546 technical instruction and training.pdf|Tektronix 547, 546, and 544 Technical Instruction and Training (PDF, needs OCR)]] -->
 
* [[Media:070-0398-00.pdf|Tektronix 547 Manual (PDF, OCR, 60MB, bad-OCR)]]
* [[Media:Tek_547_544_546_tech_instr_and_training.pdf|Tektronix 547, 546, and 544 Technical Instruction and Training (PDF, OCR)]]
* [[Media:Tek 547 fcp.pdf|Tektronix 547 Factory Calibration Procedure]]
* [[Media:Tek 547 fcp.pdf|Tektronix 547 Factory Calibration Procedure]]
* [[Media:Tek 547 cal procedure.pdf]]
* [[Media:Tek 547 cal procedure.pdf]]
<small>
'''Alternate versions'''
* [https://bama.edebris.com/download/tek/547/547.djvu Tektronix 547 Manual] (DjVu @ BAMA)
* [[Media:070-0398-00 (2).pdf|Tektronix 547 Manual 070-0398-00]]
</small>
<small>
<small>
'''Modifications'''
'''Modifications'''
* [[Media:050-0479-01.pdf|Disconnect Diode 547/R547 Serials 100-12479 (PDF)]] Tek Part [[050-0479-01]]
* [[Media:Tek 547 mods.pdf|Tektronix 547 Modifications]]
* [[Media:050-0479-01.pdf|Disconnect Diode 547/R547 Serials 100-12479]] Tek Part [[050-0479-01]]
</small>
</small>
}}
}}
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{{BeginSpecs}}
{{BeginSpecs}}
{{Spec | Bandwidth | DC to 50 MHz (−3 dB) with fast plug-ins ([[1A1]], [[1A2]], [[1A4]], [[1A5]]) }}
{{Spec | Bandwidth                 | DC to 50 MHz (−3 dB) with fast plug-ins ([[1A1]], [[1A2]], [[1A4]], [[1A5]]) }}
{{Spec | Rise time | 7 ns with [[1A1]] }}
{{Spec | Rise time                 | 7 ns with [[1A1]] }}
{{Spec | Line voltage | 90-136 V or 180-272 V, selected via primary voltage selector (inside cabinet) and voltage range selector (on rear panel), 50/60/400 Hz }}
{{Spec | Sweep Rates               | 100 ns/div to 5 s/div}}
{{Spec | Sweep Rates | 100 ns/div to 5 s/div}}
{{Spec | External Horizontal Input | 100 mV/cm to 10 V/cm, DC to 400 kHz}}
{{Spec | Trigger Coupling | AC, DC, AC LF Rej}}
{{Spec | CRT                       | [[T5470]] (154-0478-00 standard), 10 kV acceleration, 6x10 cm viewing area }}
{{Spec | External Horizontal Input | 100 mV/cm to 10 V/cm, DC to 400 kHz}}
{{Spec | Calibrator               | ~1 kHz, 200 μV<sub>p-p</sub> to 100 V<sub>p-p</sub> }}
{{Spec | CRT | [[T5470]], 10 kV acceleration, 6x10 cm viewing area }}
{{Spec | Power                     | 90-136 V or 180-272 V, selected via primary voltage selector (inside cabinet) and voltage range selector (on rear panel), 50/60/400 Hz, 510 W, AC Fan }}
{{Spec | Calibrator | ~1 kHz, 200 μ V<sub>p-p</sub> to 100 V<sub>p-p</sub> }}
{{Spec | Power consumption | 510 W }}
{{Spec | Cooling  | AC Fan }}
{{EndSpecs}}
{{EndSpecs}}


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From 11890 onward, it uses a [[152-0140-01]].
From 11890 onward, it uses a [[152-0140-01]].


===CRT===
The 547 uses the Tektronix [[154-0478-00]] CRT unless optioned for a special phosphor.
===HV Transformer===
===HV Transformer===
A common problem with 547s is the [[HV transformers|HV transformer]].  
A common problem with 547s is the [[HV transformers|HV transformer]].  
Rather than potting the HV transformer in wax, as was done up to that point,  
Rather than potting the HV transformer in wax, as was done up to that point, the [[120-0308-00|547's HV transformer]] was potted in epoxy.
the [[120-0308-00|547's HV transformer]] was potted in epoxy.
Unfortunately, this epoxy turned out to absorb moisture over time, particularly when used in humid climates.
Unfortunately, this epoxy turned out to absorb moisture over time,  
particularly when used in humid climates.
The moisture causes increased losses in the transformer.  
The moisture causes increased losses in the transformer.  
Excessive losses require the regulator to drive the [[6AU5]] input oscillator tube (V800) harder.   
Excessive losses require the regulator to drive the [[6AU5]] input oscillator tube (V800) harder.   
Eventually, the drive circuit cannot supply enough power to keep the supply in regulation.
Eventually, the drive circuit cannot supply enough power to keep the supply in regulation.
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Bernie Schroder has found that the HV transformer degeneration can be slowed considerably by keeping the HV module cool and dry.  
Bernie Schroder has found that the HV transformer degeneration can be slowed considerably by keeping the HV module cool and dry.  
The mod he was taught by Jim Willams involves replacing the tube rectifiers with NTE517 diodes.
The mod he was taught by [[Jim Willams]] involves replacing the [[5642]] tube rectifiers with NTE517 diodes to reduce the load on the regulator circuit by about 1 Watt by eliminating the filaments.
However, when the tube HV rectifiers are replaced with semiconductor types, the regulator circuit has about 1 Watt of load removed due to the lack of tube heater filaments.  
However, this can force the regulator past its design limit and result in lack of regulation, until the transformer heats up and more power is required due to losses.  
This forces the regulator past its design limit and can result in lack of regulation until the transformer heats up and more power is required due to losses.  
 
After changing to semiconductor diodes, it will be seen that grid pin 7 of V814 will be about 0 volts (fully on, with no swing to regulate)  
After changing to semiconductor diodes, it will be seen that grid pin 7 of V814 will be about 0 volts (fully on,  
in an attempt to force its anode (pin 6) to about +55 V, which is the screen input of the 6AU5 (pin 8).  
with no swing to regulate) in an attempt to force its anode (pin 6) to about +55 V, which is the screen input of the 6AU5 (pin 8).  
 
One way to remedy this is to replace the anode resistor coming off pin 6 of V814 (R803) from 56 kΩ to 82 kΩ.  
One way to remedy this is to replace the anode resistor coming off pin 6 of V814 (R803) from 56 kΩ to 82 kΩ.  
Doing so changes the grid voltage on pin 7 of V814 to a comfortable -0.8 V at switch-on.  
Doing so changes the grid voltage on pin 7 of V814 to a comfortable −0.8 V at switch-on.  
 
Again, this becomes more negative as the losses inside the transformer increase, but not by much if the transformer is healthy.
Again, this becomes more negative as the losses inside the transformer increase, but not by much if the transformer is healthy.
A second path to thermal runaway on early serial numbers is C808, which resonates the transformer primary winding.  Tek used a Sprague 160P DiFilm Black Beauty.  In the 2020's, 160P's are exhibiting high Dissipation Factor when warm, enough to self-heat in this case.  Replace with any modern capacitor.


===Vertical Amplifier===
===Vertical Amplifier===
The 547 has a five-stage BJT vertical amplifier that is fully differential from the plug-in
The 547 has a five-stage BJT vertical amplifier that is fully differential from the plug-in connector to the CRT vertical deflection plates.  
connector to the CRT vertical deflection plates. There is one tube in the vertical signal path,
There is one tube in the vertical signal path, a [[12AT7]] acting as a unity-gain buffer between the plug-in connector and the vertical amplifier.
a [[12AT7]] acting as a unity-gain buffer between the plug-in connector and the vertical amplifier.


====Spoiler Switch====
====Spoiler Switch====
The plug-in bay of the 547 has a "spoiler switch" that only enables the full bandwidth of the 547's
The plug-in bay of the 547 has a "spoiler switch" that only enables the full bandwidth of the 547's vertical signal path
vertical signal path when certain relatively modern plug-ins are used, such as the [[1A1]], [[1A2]], [[1A4]], and [[1A5]].
when certain relatively modern plug-ins are used, such as the [[1A1]], [[1A2]], [[1A4]], and [[1A5]].
 
Those plug-ins have a small hole to the left of the plug-in to mainframe connector, so they can be fully inserted without pressing the spoiler switch.
Those plug-ins have a small hole to the left of the plug-in to mainframe connector, so they can be fully inserted without pressing the spoiler switch.
(Spectrum analyzer plug-in Types [[1L30]] and [[1L40]] have the hole too but for no reason since their vertical output is low frequency.)
(Spectrum analyzer plug-in Types [[1L30]] and [[1L40]] have the hole too but for no reason since their vertical output is low frequency.)


* [[Media:Spoiler switch rationale from Tek 547 544 546 tech instr and training.pdf|Spoiler switch explanation excerpted from Tek 547 544 546 Technical Instruction and Training (PDF)]]
* [[Media:Spoiler switch rationale from Tek 547 544 546 tech instr and training.pdf|Spoiler switch explanation excerpted from Tek 547 544 546 Technical Instruction and Training]]
* [[Media:Spoiler switch rationale from Tek 547 notes.pdf|Spoiler switch explanation excerpted from Tek 547 Notes (PDF)]]
* [[Media:Spoiler switch rationale from Tek 547 notes.pdf|Spoiler switch explanation excerpted from Tek 547 Notes]]


====Delay Line====
====Delay Line====
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===Power Supply ===
===Power Supply ===


The 547's power supply provides regulated outputs of −150 V, +100 V, +225 V, +350 V, as well as a +325 V unregulated output for CRT HV section.
The 547's power supply provides regulated outputs of −150 V, +100 V, +225 V, and +350 V, plus a +325 V unregulated output for the CRT HV oscillator.


Multiple secondary windings feeds diodes for rectification for different voltages, using both center-tap and bridge configurations. The regulator section uses no transistors, only tubes.
Multiple secondary windings feed diodes for rectification for different voltages, using both center-tap and bridge configurations.  
There are multiple 6.3 V secondary outputs for heaters, some elevated to different voltage levels based on the section/tube that is supplied, in order to keep the heater-to-cathode voltage level within limits.
The regulator section uses no transistors, only tubes. There are multiple 6.3 V secondary outputs for heaters, some elevated to different voltage levels  
based on the section/tube that is supplied, in order to keep the heater-to-cathode voltage level within limits.


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.
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.
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A [[12AX7]] is used as the comparator and two [[6CW5]] in parallel are used as series pass tubes.
A [[12AX7]] is used as the comparator and two [[6CW5]] in parallel are used as series pass tubes.
A [[6AU6]] is used as an error amplifier.  
A [[6AU6]] is used as an error amplifier.  
Most other power supply sections in the 547 replicate the same basic design, except slight changes in tubes used: the +225 V and +100 V regulators employ a [[6080]] as the pass element, and +350 uses a [[6CW5]].  
Most other power supply sections in the 547 replicate the same basic design, except slight changes in tubes used:  
The +225 V and +100 V regulators employ a [[6080]] as the pass element, and +350 uses a [[6CW5]].  


The plate voltage delay circuit is similar to that found in many may other Tek scopes of the same era.  A [[6N030T|6N030T delay tube (P/N 148-0021-00)]] controls a relay that switches plate supply voltages on only after the tubes are warmed up.
The plate voltage delay circuit is similar to that found in many may other Tek scopes of the same era.   
Heater voltage is applied to all tubes immediately when the power switch is turned on.
Heater voltage is applied to all tubes immediately when the power switch is turned on.
A [[6N030T|6N030T delay tube (P/N 148-0021-00)]] controls a relay that switches plate supply voltages on only after the tubes are warmed up.


==Links==
==Links==
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Tek_547-TunnelDiodes-Trigger.jpg | Tunnel Diodes TD253 and TD3A in a Tek 547 Trigger/ Sweep Section
Tek_547-TunnelDiodes-Trigger.jpg | Tunnel Diodes TD253 and TD3A in a Tek 547 Trigger/ Sweep Section
Tunnel_DIode_1D2_2.2mA.jpg | 2.2 mA Tunnel Diode in 547 Delay Pickoff
Tunnel_DIode_1D2_2.2mA.jpg | 2.2 mA Tunnel Diode in 547 Delay Pickoff
Tek_547_Vert_Amp.jpg | Tek 547 Vertical Amplifier  
Tek_547_Vert_Amp.jpg | Tek 547 Vertical Amplifier. The output transistors are mounted on [[beryllium oxide]] discs.
547_01.JPG|Top
547_01.JPG|Top
547_02.JPG|Right
547_02.JPG|Right
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</gallery>
</gallery>


==Components==
{{Parts|547}}
{{Parts|547}}




[[Category:500 series scopes]]
[[Category:500 series scopes]]
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