I have a bunch of 5752, 6AS6 and bunch of the Russian equivalents and all of them are too microphonic. 6J7 and 6SJ7 work well, they just need about 10 times more control voltage than 6AS6. It's very easy to overload suppressor controlled vari-gain stage. If I were playing with suppressor controlled vari-gain stage again I would use 6SK7 and take the full control voltage to G3 and from there with a voltage divider to G1. Then again single ended 6SJ7 G3 controlled vari-gain stage can be a nice distortion generator.