I'm a first time builder,had been testing my SE prototype with KT88 and its work fine,when I build the final amp,the biasing goes way to high,my prototype is set at -20V,the actual is 19V,which is fine,but on my final amp,the voltage keep shooting up till the resistor burned,I measure the voltage and it goes up to 50V and seems that it want to climb further more,what have I done wrong?
Like this,
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I'm no expert in valve circuitry beyond the basics but if you have a prototype that is OK and the final build is not then three things come to mind, firstly, a basic error in transferring the design over, secondly, are you using the same KT88 as in the prototype ? and thirdly, is the design somehow oscillating. Transformer connections OK ? Have you scoped it ?
Try running it with the 3.3uf grid coupler removed and also the 2.2uf bypass. See if its DC stable in that condition. I assume you have the output tranny terminated into a load at all times.
Try running it with the 3.3uf grid coupler removed and also the 2.2uf bypass. See if its DC stable in that condition. I assume you have the output tranny terminated into a load at all times.
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