hey ekadek yr circuit looks great ...did you desgin it,I already had yr shematic on my PC ,dont no where I got it, sadly Im not clever enough to make it better maybe someone is lurking here who can help...I tend to copy circuits & try to imrove or should I say make them better for my purpose which is just to record vocals into PC, Im starting to understand how they work but not right down to the nuts & bolts...I copied the circuit for the BA6A a few years ago now, & have been using & tweaking it ever since I dont no how a real one sounds but mine sounds good to me...like you I experimented with the diode feed capicitors I had bigger values for a while but yes the bigger values made it crush more due to bass, I do like to add switches tho so I can have this feature but I like to have a switch for the original sound too as Iv learnt I can wander off the path of how its meant to sound...I find my BA & other vari mus have way too much level for my modern sound card & have been experimenting with pads & a threashold level pot ( I see you include a threashold pot on yr vari mu) Im finding the pad alters the sound for the worse & having been thinking of designing my own vari mu....I know they need the power output stage to drive the rectifier to get quick enough attack so I was thinking of tapping my audio from earlyer in the circuit...to get the levels low enough Im having to crush more than I want...like i said I have my own threashold pot & if Iv done this correct Iv measured the bias voltage ??? which goes from 0V to 144V I think...In the BA manual it should be a fixed 66V as there is no threashold pot so I figure that if I set my pot so bias reads 66V then Im in the BA6 original threashold state ...I hope ? but in that condition I need to drive it harder cause more output.
Your output attenuator looks interesting ....what of attenuation levels does that give ? is that a T type atten ?
& whats the bottom 12AU7 is that like an active attack thingy ?
Is that a interstage transformer I see ?
& what transformers are you using ?
sorry for all the dumb questions hope you dont mind
Iv enot seen any limiters with EF83s in yet so thats interesting..I wired a pair of 6BA6s as triode and as if they were 1 X 6386 I grafted in onto the input of ny BA instead of its usual 12SK7s I tried different cathode resistors & so on I set the tubes up as in other circuits like the gates & collins but they didnt sound as good as the original I spose because it wasnt designed for those tubes...
Ive just been fiddling with a VK1 circuit.. copy of Altec 436C but with none vari mu ECC85 tube input ECC81 output ....the over all sound was great ( with BA6 output tran) & levels were more managable, but the limiting effect was crap for vocals maybe I could graft the 12SK7s BA input in place of the ECC85