Over the next few months I shall attempt to make a U73b limiter/compressor from scratch. This project will (hopefully) be a tribute to Oliver Archut who we very sadly lost last year and who has been solely responsible for collecting the Telefunken Archive from which many of us have benefited.
This will be the first feed-forward limiter that I’ve made and Ruairi O Flaherty has kindly offered to test it for me (he is a mastering engineer).
I will be copying the original circuit closely but with a few exceptions:-
1. I will be using a matched pair of 6BJ6’s which I already have, they are the US equivalent of E99F’s
2. I will be using DC for the heaters.
3. I will use an ECF80 instead of an E80CF as I already have one.
4. I will use a resistor load instead of a choke in the make-up amp, this will reduce the output but I am using a 15k:600/ 5:1 OPT instead of the 10:1 in the original which should help with the loss.
5. I will be making a rack mount chassis to give me some more room to play with.
6. I won't be including the balance test circuit, I don't want TX hum near the input grids.
I will cover some side issues in the course of the build which I hope will be useful:-
1 Splitting the primary of an Edcor XSM matching TX.
2. A series of tests on transformer screening.
3. An alternative to the expensive E88CC using TV tubes.
I’ve attached a redrawn schematic out of respect for Oliver’s estate. I have used the original component numbering system as far as possible for reference. If you want to check out his site you can find it here:-
http://www.tab-funkenwerk.com/id6.html
Best
DaveP
This will be the first feed-forward limiter that I’ve made and Ruairi O Flaherty has kindly offered to test it for me (he is a mastering engineer).
I will be copying the original circuit closely but with a few exceptions:-
1. I will be using a matched pair of 6BJ6’s which I already have, they are the US equivalent of E99F’s
2. I will be using DC for the heaters.
3. I will use an ECF80 instead of an E80CF as I already have one.
4. I will use a resistor load instead of a choke in the make-up amp, this will reduce the output but I am using a 15k:600/ 5:1 OPT instead of the 10:1 in the original which should help with the loss.
5. I will be making a rack mount chassis to give me some more room to play with.
6. I won't be including the balance test circuit, I don't want TX hum near the input grids.
I will cover some side issues in the course of the build which I hope will be useful:-
1 Splitting the primary of an Edcor XSM matching TX.
2. A series of tests on transformer screening.
3. An alternative to the expensive E88CC using TV tubes.
I’ve attached a redrawn schematic out of respect for Oliver’s estate. I have used the original component numbering system as far as possible for reference. If you want to check out his site you can find it here:-
http://www.tab-funkenwerk.com/id6.html
Best
DaveP