516F-2 After Installation of Service Bulletin #1

Here is a great shot of an installed PCB by N2ZZ. This is a late model PCB (2019+). There have been several version of the PCB. Changes were made to accommodate different component sizes. In 2021 the international parts shortages are becoming much more acute. The particular caps were chosen to allow various vendors sizes to be used. Depending on availability, you may receive components which look different than are shown in this photo.

The provided Wago brand Lever Nuts are preferred for the Buck filament wiring. Note that some wires required extensions to reach the intended attachment points on the PCB. The soldered joints with heat shrink make a nice looking installation.

Over 400 kits have been shipped. 2 have been returned as the customer thought the challenge was too much. There was never a customer who couldn’t make the kit work. The PCB assembly is trivial. The mechanical installation is the challenge as you must drill out the rivets to remove the original cap holders. Then you have to get the new screws under the transformer.


The kit includes all components shown on the PCB: diodes, caps, resistors, relay (220V relay is a no charge option. Please email) Hardware is size 4-40 stainless with aluminum posts. The new AC line cord is grey (there are various versions of grey).

Here’s a GREAT success story from Chris M1ABK

What You Get:

  • New PCB which accommodates:
    • All New Diodes (11 total)
    • AC Relay (protects the obsolete On/Off switch from surges)
    • Caps 8x (C1..C7)
    • Resistors R1..3 for HV load balancing and R8 & R10 for Bias range adjustment
  • Gray Line Cord (Insulation on the old one is brittle and unusable)
  • Line Cord Clamp (new plastic clamp)
  • Mounting hardware (#4 screws, hex posts, & washers)
  • Wago Lever Nuts (for using the 5v secondaries in Buck configuration)

Shop carefully. There are other kits which offer substantially less for nearly the same price. As you will quickly determine, the existing AC line cord is shot. The insulation is brittle and cracked. Be sure to buy a kit that includes a new AC LINE CORD!

You could hack a similar kit together buying plugin diode modules from one vender, a relay kit from another and ill fitting caps from a third. Get it all in one integrated package.

Who better to design this mod than 2 retired Collins engineers from Cedar Rapids! WØIY and KØDAS

NOTE: We are hearing from a number of users that are having difficulty following the color codes provided in the instructions. It appears that a significant percentage of power supplies have been repaired or modified over the years. The mod work did NOT necessarily maintain the same colored wires. We’ve even seen power supplies wired almost entirely with white wire. There are also instances of the same colored wire being used in several very unrelated portions of the circuit. Therefore, you should do the PCB installation and chassis wiring using primarily the schematic, with the wire colors as secondary guidance. WØIY 2016-10

Flexible Assembly

Build up all the components or just as much as you’re comfortable. The pcb is designed to allow using any or all of the circuit.

Want to retain the 5U4 and 5R4? No problem!

Here are the instructions for retaining V1 and V2.

As there are a huge variety of thoughts on using the solid state rectifiers, you should determine which approach is assembly is the most consistent with your personal philosophy.

The most conservative approach is to install

  • · The electrolytic caps in the High Voltage and Low Voltage
  • · All components for the Bias Supply
  • · The AC relay
  • · Line cord

If you elect to install the solid state diodes, it is strongly recommended that the now unused filament windings be used to “buck” the primary, reducing the secondary voltages. This mod is supported by very nice Lever Nuts which allow the wires to be swapped in to change the phase of the secondary winding.

The MUCH Needed Relay

Users also have concerns about the On/Off switch in their rigs as the switch/pot combo is obsolete. A modern relay with 12A contacts is included.

Resource Page (Schematics, Photos, etc) (Updated 2015-1-12)

It has come to my attention that some folks can not open this link. Possibly it requires you to be signed into Google or Gmail. If you can’t see the page, just email me and I’ll send you the files via email. Sorry for the inconvenience.

Packing List

Instructions are maturing nicely, thanks to comments from customers. Please email comments or questions on any of the documentation.

See them here: 516F-2 SB-1 Instructions (Updated 2015-01-12)


The user needs to remove all of the old components and drill out the spring clips. This is relatively easy. Hex posts are installed and the PCB mounts on the new posts (supplied). Hookup wire is not supplied.

Moderate mechanical and soldering skills are required.

BE SAFE! Use eye protection and make sure everything is unplugged before beginning the installation.