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Old 27th Jul 2017, 6:54 pm   #40
Heatercathodeshort
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Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 7,755
Default Re: Kolster Brandes RV 10 (Crown)

This evening I thought I might clarify a simple substitute LOPT test utilizing practically any line output transformer of any make.

The example I have here is from a Ferguson 506T I scrapped years ago. Before you start mourning it was filthy, disgusting, knobless and the cabinet was bashed to bits!

As you can see all I have done is remove the top cap connections from the PL81 and PY81 in this case a PYE V14C and connecting them via some croc clip extension leads to the corresponding connections on the Thorn 506T transformer. No other connections or disconnections were made.

As you can see good EHT is developed in the test transformer to the extent that the EY86 EHT rectifier lights up producing healthy EHT. This can be seen as I draw an arc from the anode connection. [Try holding a smartphone and drawing an arc at the same time]

I played around a bit more. If you don't have a scrap LOPT, delve down your junk box and find an old audio output or mains heater transformer. Connect the primary to the PL81 and PY81 [or any other timebase valves that may be incorporated in the test receiver] and the secondary to a 6.3v .3amp scale light lamp. As you can see with the line output stage working correctly the lamp will light.

This test will work with any receiver that has an independent line oscillator not dependent on any feedback pulse from the primary of the lopt.

It's a crude test but practical and will determine if the damped line output stage is due to shorted turns in the line output transformer itself.

With a little practice you can get to 'read' the results and arrive at a satisfactory conclusion. John.
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Last edited by Heatercathodeshort; 27th Jul 2017 at 7:12 pm.
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