Quote:
Originally Posted by GrimJosef
The hiss usually arises in the earliest stage of the amplifier i.e. the EF86 and its circuitry. Some EF86s are noisier than others - all you can do is work your way through a few, listening for the quietest one. Another possible source is the anode and screen grid resistors. Mullard specified that these should be 'high-stability, cracked carbon' types for precisely this reason. These days we would call them 'carbon film'. Modern metal film ones are even quieter, but, as always, it's important to make sure that they are not running too close to their voltage limits.
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GJ has already mentioned the carbon composition resistors being a possible cause of noise around the EF86. Suggest you replace these with modern carbon film types.