Is there any reason for exceeding the 70% recommendation in the HT-40? Is it something unique to how the amp is set up? The second is at about 82% after the tube swap and adjustment. In the first example, the tube dissipation is almost 78% of max. In both these cases, the recommendation of 70% max tube dissipation for tube life (25w max for el34s, 17.5w at 70%) is being exceeded, before and after in the first case, and at least after adjustment in the second case (and must have before too). In one case I have come across, the person replaced their tubes and ended up with almost the same plate voltage and bias before and after - 380V 51mV and 379V 54mV respectively.Īnother person had 51.5mV beforehand (no plate voltage), 32.4mV after with 402V when putting in new TungSols, which he in turn increased to around 50mV. It seems like most people are just biasing their tubes to 50mV without any regard for plate voltage.
You can see by the TP 10 and TP 18 test points 50mV printed on the board.
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