I have a number of Drake A, B, and C twin combos. I decided to upgrade all the power supplies with AC-4R boards. Since most of the caps are now 30 to 40 years old, I don't want to risk a bias supply going out and ruining the finals or some short ruining the transformers. I order a bunch of blank boards since I already had some of the parts. The rest of the parts I ordered from DigiKey. I assembled all the boards at the same time and then started upgrading the AC-4s, one by one.
So far, all of the power supplies are different in one way or another and all of them have been modified by previous owners. Here are some examples: #1) A previous owner replace the mid-voltage supplies' capacitors with a bundle of three caps mounted to the upper end the supply. #2) A previous owner replaced the sand resistor below the chassis with two higher wattage resistors mounted to the upper end of the supply. #3) A previous owner replaced one of the diodes in the HV supply. The transformer in this supply has transformer bolts inserted the wrong direction to mount the AC-4R board. Unfortunately, it's not as simple as removing the bolts and inserting them in the other direction because the bolts are just long enough to reach, but not long enough to add the board spacers. #4) This is an AC-3, serial #101. I've never seen a Drake power supply like this. There's a large choke mounted adjacent to the transformer. All of the other parts, including the capacitors, are radial lead caps that are packed underneath the very low chassis. Has anyone else seen an early AC-3 like this? I'm planning to remove the choke and rebuilding the supply just like all of the others since all of the circuitry is now on the AC-4R board. Thanks, Tom N7TM
