HV transformers: Difference between revisions

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In many classic scopes, the high voltage transformer that supplies the cathode, blanking, and anode voltages has a tendency to break down.   
In many classic scopes, the '''high voltage transformer''' that supplies the cathode, blanking, and anode voltages has a tendency to break down.   
This is mostly because of aging of the potting material used for the high-voltage windings.  It will running very hot, because dielectric loss is too high. It is a thermal runaway.
This is mostly because of aging of the potting material used for the high-voltage windings.   
When this happens, the transformer will run very hot because dielectric loss is too high.  
It is a thermal runaway.


Currently, the only options when this happens are to find a similar transformer from another scope,
Currently, the only options when this happens are to find a similar transformer from another scope,
or to get a rewound transformer.
or to get a rewound transformer.


Inofficial second options is good cooling of high voltage transformer (It is testing by 556´s HV-transformer)
A second option is to improve the cooling of the high voltage transformer.
This approach has been tested with success on a 556's HV transformer.


The same HV transformer, part number 120-0308, is used in the [[543|543B]], [[544]], [[545|545B]], [[546]]and  [[547]] .
The same HV transformer, part number [[120-308]], is used in the [[543|543B]], [[544]], [[545|545B]], [[546]] and  [[547]] .
Chuck Harris, who frequents the Yahoo Tekscopes forum, has rebuilt several 120-0308 transformers with good results.
Chuck Harris, who frequents the groups.io (formerly Yahoo) Tekscopes forum, has rebuilt several 120-308 transformers with good results.
 
[[Category:Repair issues]]


==Documents==
* [[Media:HV Transformer Tek 500 Series-Rev 02.pdf|"HV Transformers for Tektronix 500 Series Scopes Wound on ETD44 Core" by Marco Morelli]]


==Pictures==
<gallery>
<gallery>
File:KeepcoolHV.JPG | Inofficial seconds options: cooling with aluminium-block
KeepcoolHV.JPG | Alternative to replacement: cooling with a heat sink
120-466-0x.JPG | Two different HV transformers for [[561B]] & [[568]]. Brown potting ([[120-0466-00]]) is bad, clear potting ([[120-0466-01]]) is ‎an improved variant to avoid the thermal runaway problems.
</gallery>
</gallery>
[[Category:Repair issues]]
[[Category:Inductors and transformers]]

Latest revision as of 05:08, 7 April 2021

In many classic scopes, the high voltage transformer that supplies the cathode, blanking, and anode voltages has a tendency to break down. This is mostly because of aging of the potting material used for the high-voltage windings. When this happens, the transformer will run very hot because dielectric loss is too high. It is a thermal runaway.

Currently, the only options when this happens are to find a similar transformer from another scope, or to get a rewound transformer.

A second option is to improve the cooling of the high voltage transformer. This approach has been tested with success on a 556's HV transformer.

The same HV transformer, part number 120-308, is used in the 543B, 544, 545B, 546 and 547 . Chuck Harris, who frequents the groups.io (formerly Yahoo) Tekscopes forum, has rebuilt several 120-308 transformers with good results.

Documents

Pictures