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Rogers Ravensbourne - thermistor advice!

Markoneswift

Markoneswift

Quartz locked n ready to rock
Hi all - I'm restoring a lovely old Rogers Ravensbourne integrated amp, but I a problem with the power supply. There are four thermistors between the transformer secondary windings and the rectifier diodes. All of these thermistors - Mullard VA1033 - have crumbled away to dust.

What I'm thinking of doing is replacing them with similarly rated resistors - just to get power into the amp, so I can check / verify other areas. Would there be any major concerns about this approach? I appreciate that the thermistors are there to control thermal runaway etc but I'll only be running it to test and not under any load.
 
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Should be able to do that. Looks like a 3.9 or 3.3 ohm resistor would suffice for testing. If its in the power supply rather than the bias supply it shouldn't be overly critical. Sitting between transformer and rectifier, the only purpose I can really see it serving is to lower the inrush of charging the main filter caps. It wouldn't have anything to do with thermal runaway or anything like that.

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One thing I am in the dark about is voltages - idle / bias etc - can't seem to find any figures for those type of settings anywhere. Normally. I would expect these to be in the service manual under 'adjustments'
 
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