Phono 3 with 5751 valves

[Richard]

I've been trying 5751 valves in Phono 3 this past week. Lovely. I used them a few years ago instead of ECC83 in my 5-20 monobloc poweramps, thought they were good then, and have been meaning to try them in here for a while.

They have a little less gain than ECC83 with mu of 70 instead of 100. With the first stage bypass cap mod fitted, gain is now just a little more than standard (ECC83 and no bypass caps). The sound though is better than the 3 ECC83 types I'd tried before. Natural, transparent and airy are the words that come to mind. I'm not saying they're better than everything else, just that they're another flavour that can be tried without any problems

I checked RIAA response after fitting and there was a slight lift from 10KHz to 20KHz. Square wave confirmed an overshoot. This tells us the high frequency output was greater. A small adjustment of the trim caps corrected this easily (for anyone not using test gear the trim caps end up just past middle of the adjustment range - see pics later). Once this is done the response is ruler flat. The reason for this lift is the slightly lower plate resistance of 5751 compared with ECC83.