VariMu/Com from scratch

[Lampie519]

I would like to build a U73 kind of compressor/limiter but no clone as i do not have original transformers. Therefore it makes no sense to even try to clone one. But the functionality and audio quality must be spot-on even with transformers i have at my disposal.
The side chain can be solid state and so can be the Varicom circuit as i do not see any advantage of having it all tubes (hybrid is an option here).
Any thoughts are welcome...

 

[gyraf]

Post schematic, relevant info about what you have at hand, and excatly what you want to do?

/Jakob E.

 

[Lampie519]

I will start off with 2x E99F tubes as in the original with 2 transformers (input and output of this stage, attached some specifications of these transformers) but as i don't have a inductor for the last stage i will have to think about an alternative circuit. Maybe a beefier triode and a resistor load or some kind of follower (no SRPP as i don't like their sound). I will post a schematic soon.

 

[Lampie519]

Here a gain stage with buffer i made up. This way it does not add too much of a sound and can easily drive the next stage (a transformer on the output is not needed if unballanced is ok).

 

[Lampie519]

Naturally the transformer could be attached to the screen grid but then there will be a little DC running through it and maybe a bit noisier as it is connected to the B+ instead to ground.
i also found a couple of small transformers that could be used here. Must check the frequency response though.

 

[Lampie519]

As i integrate the Varicom into the one box compressor i don't need an additional preamp so i will increase the gain of the next amp in order to reach the level needed (that should be easy just less clamping). Also i am not sure if i will have a "stereo"version or just make it a dual mono version with ganged switches (so the setting are the same in any case).