Recently rearranged a couple of Gates SA series preamp racks I’ve been using a long time, this was spurred by the desire to take these out on an Avett Brothers remote recording job. The SA-70’s were in a frankensteined SA-700 rack case, on which someone hacked the rear to be SA-800 sized, and had no front panel controls or connectors. The SA-94’s were in an SA-800 case that was a little more cosmetically challenged, so I swapped cases with the new control escutcheons hiding more scrapes. It took a number of years to find 5 of of the original Gates escutcheons.
The SA-94 rack was previously covered here:
https://groupdiy.com/index.php?topic=28450.msg343899#msg343899
First up is the impressive hacking of the SA-700 case. A bit of custom metalwork with welding, and careful cutting of the case.
Re-racked SA-94’s
SA-70 rack rearrangement
The connector panel and spacer had to be odd sized, and barely fit. The answer was to cut down a piece of L bar.
Interstage gain controls are moved off module onto the front panel, using Daven pots. I’ve done this before with standard pots on other re-racks, and have to say response at intermediate gain settings is much better with the Davens. Standard pots start to show some treble roll-off, but there’s no change here at all.
I burned in a new set of 6J7’s and 6C5’s, then looked at gain/response/noise compared to the tubes that have been in there since the early 2000’s, and found no real degradation in the used tubes. Current was slightly lower, but that was it.
I listened to a number of PSU’s I have here, mostly rebuilt tube regulated types, and didn’t find any appreciable noise difference. The SA-94’s are still on the General Radio, and for now the SA-70’s are still on a Heathkit. I have a Gates SA-40 console PSU (CLCLC) which would be the right matched piece that I need to try after a recap, it would add another 5RU though. In practice these are fine with AC filaments. This rig went out on a remote recording job which was acoustic duo, mix of condensers and ribbons.
The SA-94 rack was previously covered here:
https://groupdiy.com/index.php?topic=28450.msg343899#msg343899
First up is the impressive hacking of the SA-700 case. A bit of custom metalwork with welding, and careful cutting of the case.
Re-racked SA-94’s
SA-70 rack rearrangement
The connector panel and spacer had to be odd sized, and barely fit. The answer was to cut down a piece of L bar.
Interstage gain controls are moved off module onto the front panel, using Daven pots. I’ve done this before with standard pots on other re-racks, and have to say response at intermediate gain settings is much better with the Davens. Standard pots start to show some treble roll-off, but there’s no change here at all.
I burned in a new set of 6J7’s and 6C5’s, then looked at gain/response/noise compared to the tubes that have been in there since the early 2000’s, and found no real degradation in the used tubes. Current was slightly lower, but that was it.
I listened to a number of PSU’s I have here, mostly rebuilt tube regulated types, and didn’t find any appreciable noise difference. The SA-94’s are still on the General Radio, and for now the SA-70’s are still on a Heathkit. I have a Gates SA-40 console PSU (CLCLC) which would be the right matched piece that I need to try after a recap, it would add another 5RU though. In practice these are fine with AC filaments. This rig went out on a remote recording job which was acoustic duo, mix of condensers and ribbons.
