Federal 864 chassis repurpose ideas

[burdoto]

I built two federal 864 limiters a long while ago and I want to reuse one of the chassis and the octal sockets for a different design of some kind. I like dirtiness of the federal, but I don't think I need two of them. I've read all the federal threads out there I think and the couple redesign threads here. I've build a BA6A and I probably don't need another one, but it is very impressive. I've looked at the Western electric 1126 schematic for ideas which one of the other federal related threads discussed. I've read the 6j5 is the predecessor to the 6sn7. Also read the 6cg7 is the nine pin version of the 6sn7 which the rs124/altec 436 uses and performs significantly better. Right now the unit has a BA6A vari-mu section and 6h6 sidechain(including the OD3 regulator) fed by the 6sn7 plates. The circuit works better than I expected given that it should be driven a 6v6 power stage. Would probably benefit from lower 6sk7 screen voltage. I've looked at the Collins 26u which also has 6v6s. So there seems to be power tetrodes and medium-mu tubes used as outputs for these comp/limiters. I know there are other circuits out there. Are there other output tubes I should try? I can add more sockets and I have a 260-0-260 90ma power transformer I can use. I got a 10k/600 OT, but I can try something else. It's been suggested the 6sn7 would like a higher load. Is a medium-mu plenty capable a delivering decent attack times and ratios for studio use or is a stronger output time needed. 6v6s seem a little intense although the BA6A is pretty intense.

I've figured it's time I ask some questions. I could use a little more theory I'm sure. Stronger output tubes? Is Higher plate voltage on the output tubes required for faster performance? I also don't which parts of the circuit determine the ratio of a vari-mu. I'm not sure how much variety there is with vari-mu comps/limiters. The redesign could be a limited or comp or both.

Any suggestions?

 

[emrr]

In traditional use, output power relates to maximum threshold.  If you're building a slower time constant comp without a dedicated side chain drive amp (like most) then you can use lower power output tubes.  6K6 6F6 6Y6 6W6 etc.  6N7.  6N7.  Lots of choices. 

 

[burdoto]

I've read the 6SN7 is a pretty hardy tube.  Should I demand more from it? Higher Plate voltage?

I may be wrong, but the Federal is pretty slow and I think the output distorts because of it.  I want a comp with  enough juice for faster attack times if needed.

 

[burdoto]

Are there schematics I should check out for ideas? Is there a compressor/limiter that uses a sidechain driver I should check out? The UA 176 seems to use transformer taps on the primary for different ratios. Is because of the resistance between the tap and the plate or the impedance?

Also, I use a pentode output section should i use a second stage with feedback from the output tubes to the second stage like most of these limiters seem to? I assume the two stage output section was to achieve a balance between distortion and power?

Also, the western electric 1126 is interesting to me. 6j5 output tubes with a second stage. How would this limiter have performed?