84bronze wrote:
193J is a 10H 150mA choke while the suggested replacements are 7H or 6H. So is it the Henries don't matter and try to get the mA to match when finding a suitable replacement. Wouldn't the Edcor CXC125-10H-200mA be a good substitute?
I apologize for the confusion. It all goes back to the history of the Lacewood amp and reuse of components.
The original Lacewood power supply was built to preclude
any chance of power supply ripple coming through to the tubes. As such, it was FAR over designed. Since I retained the choke for the V2.0 That is what got used. But let's walk through the math.
The the original power supply design has a design point ripple factor of 0.022 at the first capacitor. This equates to -33dBv of ripple. I want at least -90dBv of ripple at the tubes these days. Using the 10H-32µf filter stage gives a ripple reduction of -45dBv. This puts ripple at -78dBv. Just 12 dB shy of my target.
Now the lacewood V2.0 uses a split power supply filter with interstage isolation provided by choke filtering on each branch. This provides a lot of filtering overall because the filter factors from the two stages are multiplicative, i.e. dBs add. So looking at the second stage 1H-100µf filter, it gives a ripple reduction of -35dBv. This gives a total ripple reduction at the power tubes of -113dBv. This is a full 23dBv of filter margin.
What all this means, is that with the same second stage filtering, the main LC filter only really
needs to supply 22dBv (90-33-35=22) to meet the -90dBv requirement. If the 10H choke is substituted by a 7H choke, the new 7H-32µf filter section provides 42dBv of ripple rejection (for a total of -110dBv) and a 6H choke gives 40.6dBv of ripple reduction (for a total of -108.6dBv). So either option is more than sufficient to meet the -90dBv overall ripple requirement.
For a better understanding of filter sections, you can take a look at part 2 of my power supply article
here.
Oh... and to answer your question: Yes, the Edcor CXC125-10H-200mA would make an admirable substitute for the Hammond 193J.