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The Drake AC4R is one of the most popular kits we have sold.


You get brand new 150 mfd @450 vdc capacitors. New 150K flameproof metal film resistors and 1.5 amp 1000 vdc rectifiers. One problem with the AC4 is failure of the bias supply. With no bias on the final tubes, even in receive mode, they will conduct current and literally melt the glass. So in addition to new plate voltage capacitors and diodes this kit has new bias capacitors, new bias resistors and even new capacitors in the screen supply.

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The pcb mounts on the end of the power transformer. Assembly of the pcb is quick and easy. Connections to and from the pcb are made with wire included in the kit. While not hard to install, the kit requires cutting and splicing of wires and removal of all the old components from the chassis. Basic hand tools are required as well as a VOM that can read voltage upwards of 1000 vdc. Extensive assembly and installation instructions are included.

Kits (and assembled pcbs) come with all mounting hardware, wire and all board mounted parts.

The voltages inside the AC4 are dangerous and you can be killed or seriously injured if you get your fingers in the wrong place. Experience with assembling and testing high voltages are necessary for the safe installation of the AC4R upgrade kit.

Will this upgrade work with the Drake AC3?

Although electrically the same, the instructions are geared toward the AC4, therefore installing the kit into a AC3 will be on your own. Because the AC3 transformer is different, you can't mount the pcb to it, you will need to drill holes into the AC3's chassis to mount the pcb.

Choose from either the bare pcb or complete kit. Assembled pcbs are also available.


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The pcb mounts to the end caps of the transformer. You keep only this transformer and the bias adjust pot. All of the electrolytic capacitors are replaced. The two shown in this photo are only filling the holes; they are NOT connected to the circuit in any shape or form.
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