Would I be destroying something of historical worth by converting that early, and perhaps rare AC-3, to a modern supply? That would mean removing the choke and essentially all the parts underneath the chassis? The AC-4R (as I'm sure you're aware) replaces everything but the transformer, the cables, the connectors, and the bias pot.
On 12/11/06, Garey Barrell <[EMAIL PROTECTED]> wrote:
Tom - Yeah, that's typical. You're taking the right approach, since a failure in the Bias supply can take out more than just the finals, even if the unit is in Standby. #4. Yes, this is a VERY early AC-3. I don't know how many were made, but I've only seen a couple in 40 years of using/working on Drake gear. They work just fine, but your plan is reasonable. Drake dropped the choke, probably for cost / weight / not needed reasons. The primary reason for it originally was to improve the regulation of the HV. 73, Garey - K4OAH Atlanta Drake 2-B, 4-B & C-Line Service Supplement CDs <www.k4oah.com> Tom Taylor wrote: > 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
