I started building the V-72-S mic pre yesterday. It looks like it will fit in this small rack which will keep noise down. The rack is a surpus video router that has been gutted. Paid 10 bucks. Has a pretty heavy duty plating job which should help shielding. All the resistors are NOS German resistors from the old days. Scored them at a surplus store. Not carbon comp. That's all the parts you need for the PC board. Going to lay down the two tubes inside the chassis and solder the pins directly to the lead wires, so there will be no switches or contacts in the signal chain.
Using the Peerless K-241-D that I partially dissected a while back. Down 1 db from 3 hz to 30,000 hz without resistive termination. Has 90 db worth of shielding plus whatever I get by having it inside that compartment.:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_1.jpg
I got this nice beefy permali turret board out of some stuff I scored at Andy's garage. Same stuff used in the original V-72:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_5.jpg
I am using an external regulated pwr supply whcih will feed this additional pi filtering. Those are NOS Elkos like the original which will have to be brought up slowly. There's a NOS Phillips in there also:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_3.jpg
I hand wound this three chamber bobbin for the plate choke. I squeezed on 8000 turns of #39 without a break. Going to lam it with those 80% Super Q lams. Had to fab the seperators as nobody makes a three chamber bobbin anymore. Probably will have less inductance than the original 300 Henries since I do not have Ollie's winding machine to wind the #44 hairwire, but it should still sound good.The bobbin is the same one used in the API output.
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_4.jpg
Going to use a Triad HS-50 output transformer.
Should sound pretty good. Based on the V-72-S for EMI studios. Only difference is an extra cathode resistor in stage one, and a differently wound input transformer. I will let you know how this thing sounds.
cj
Using the Peerless K-241-D that I partially dissected a while back. Down 1 db from 3 hz to 30,000 hz without resistive termination. Has 90 db worth of shielding plus whatever I get by having it inside that compartment.:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_1.jpg
I got this nice beefy permali turret board out of some stuff I scored at Andy's garage. Same stuff used in the original V-72:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_5.jpg
I am using an external regulated pwr supply whcih will feed this additional pi filtering. Those are NOS Elkos like the original which will have to be brought up slowly. There's a NOS Phillips in there also:
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_3.jpg
I hand wound this three chamber bobbin for the plate choke. I squeezed on 8000 turns of #39 without a break. Going to lam it with those 80% Super Q lams. Had to fab the seperators as nobody makes a three chamber bobbin anymore. Probably will have less inductance than the original 300 Henries since I do not have Ollie's winding machine to wind the #44 hairwire, but it should still sound good.The bobbin is the same one used in the API output.
http://vacuumbrain.com/The_Lab/TA/Telefunken/V-72/72_4.jpg
Going to use a Triad HS-50 output transformer.
Should sound pretty good. Based on the V-72-S for EMI studios. Only difference is an extra cathode resistor in stage one, and a differently wound input transformer. I will let you know how this thing sounds.
cj