Variable Mu

[Larrchild]

I would say yes. In most circuits, you are not messing with the bias over 20-30v. That messes with Rp, if the plate supply is on the move, with current draw. To my ear, current should vary feeding these tubes, not voltage.

 

[skipwave]

Thanks. I found a detailed response from PRR about regulation in vari-gain stages in this THREAD.

Sounds like there are tradeoffs, but I will do best to go with reg'd. I've never built a regulated high voltage supply before. Guess its time to learn. :green: Sorry for the off-topic.

 

[analag]

I have been running various scenarios...very finicky side chain.
[quote author="Larrchild"]In most circuits, you are not messing with the bias over 20-30v. That messes with Rp, if the plate supply is on the move, with current draw. To my ear, current should vary feeding these tubes, not voltage.[/quote] Hear, hear...also tube devices sound a little different with regulated B+, less spongy.

analag

 

[analag]

I have been reworking the idea...I needed faster attack/recovery and truer gain control. I got it. (According to the simulator)
It now uses three tubes (1)6BC8 (or any of the other favorites) for gain control (1) 12AU7 for output (1) 6SN7 for the sidechain amp. I chose the 6SN7 for it's excellent pulse capability. The feed to the sidechain is taken right after the 6BC8. Unfortunately it now requires another transformer to perform the impedance transformation to drive the 6BC8 grids. Sidechain rectification is done with (4) 1N4148 signal diodes, forming a bridge reftifier. We now have, Gain, Reduction and Gain Makeup controls. The attack and release setup is not yet implemented, but so far it's looking a lot like the compressor discussed in the other thread.

analag