Blue Jinn
Well-known member
I was thumbing through an old ARRL handbook, which had a 6AL5 based side chain for a speech compressor. It looked cool. the input was 'parallel' with the grid of the last triode, before the power stage, and the input to the suppressor grid of the first stage noting that it required a circuit with a pentode input. I'm not a designer by any means, and I googled the heck out of this. Did come across discussions using a 6AL5, and also the "Li'l 4x4" which uses a similar concept, except not with the suppressor grid. I have no idea how to calculate the gain reduction using that method (I generally have no idea how to calculate a lot of things, which is why I hang out here trying to learn things) but I wanted to take a crack at it anyway to see if anything made sense. I took the pentode part numbers straight out of the RCA tables for a 6AU6 which seemed close enough to a 6BA6 (what I read suggested you use a remote cutoff pentode) the triode parts from Zugster's triode gain calculator, and the side chain straight out of the ARRL book. (Except I put in larger value pots in place of the fixed resistors for the attack/decay.)
I didn't find anything like this googling, so I am pretty sure I am barking up the wrong tree here, but thought I'd put it up for criticism anyway. Again, I haven't attempted to do any proper math here, and I have no clue how to calc the gain reduction. Also, I am not 100% certain there should be a pot on the input to the triode. The book called for a "single plate to push pull grids" interstage transformer, so I just took a swag at 1:2.
EDIT: I am also not sure I need all that gain on the pentode, so assuming I could strap the screen to plate instead, and other changes to part values. (And maybe do some math...)
EDIT 1: I did omit a blocking capacitor on the output by mistake.
I didn't find anything like this googling, so I am pretty sure I am barking up the wrong tree here, but thought I'd put it up for criticism anyway. Again, I haven't attempted to do any proper math here, and I have no clue how to calc the gain reduction. Also, I am not 100% certain there should be a pot on the input to the triode. The book called for a "single plate to push pull grids" interstage transformer, so I just took a swag at 1:2.
EDIT: I am also not sure I need all that gain on the pentode, so assuming I could strap the screen to plate instead, and other changes to part values. (And maybe do some math...)
EDIT 1: I did omit a blocking capacitor on the output by mistake.