In two weeks time I will be starting the recreation of a 1947 Gates 28CO.
This is an interesting compressor as it is based on the changing resistance of light bulbs, which makes a change from the many vari-mu designs that came after it. It started life in 1937 as the 17B
But that had no provision for release so after WW2 in 1947, Gates came up with the 28CO which incorporated an adjustable release control. This was unusual in that it was derived in a similar way to Vari-Mu types but they used low noise 6J7's instead of Vari-Mu tubes, equally unusually they applied the negative voltage to grid three of the pentodes instead of Grid 1. I have tested this and it does work ok; it is a very subtle effect.
The original is a large unit about 7u high but I will be making it 3u size with modern components. It still uses 5 audio transformers though!!!
This is the original 28CO:-
Thanks to EMRR for the pix.
I expect the 28CO to have an interesting and unique sound.
best
DaveP
This is an interesting compressor as it is based on the changing resistance of light bulbs, which makes a change from the many vari-mu designs that came after it. It started life in 1937 as the 17B
But that had no provision for release so after WW2 in 1947, Gates came up with the 28CO which incorporated an adjustable release control. This was unusual in that it was derived in a similar way to Vari-Mu types but they used low noise 6J7's instead of Vari-Mu tubes, equally unusually they applied the negative voltage to grid three of the pentodes instead of Grid 1. I have tested this and it does work ok; it is a very subtle effect.
The original is a large unit about 7u high but I will be making it 3u size with modern components. It still uses 5 audio transformers though!!!
This is the original 28CO:-
Thanks to EMRR for the pix.
I expect the 28CO to have an interesting and unique sound.
best
DaveP