You should be familiar with the 516F-2 power supply and competent to perform the modifications. If you have questions please send email to barry.w0iy@gmail.com Unassembled kits may be returned for a refund (no refund on shipping charges).
We request your feed back on the kit and the instructions.
1. Options
Before you begin, you need to make some choices:
Rectifiers
Either type of rectifier is acceptable, it just makes a minor difference in wiring the chassis to the PCB. The instructions provided are for the solid state diodes on the PCB. The original schematic and the modified schematic should be consulted before proceeding. All connection terminals on the PCB are clearly labelled to facilitate partial modifications.
Regardless of which rectifiers you use for HV and LV, you should remove the old bias selenium rectifier with the diode. When the selenium dies they smell horrible and smoke is likely a carcinogen.
C1
There have been instances of shorted C1 (original component). This changes the power supply topology to a capacitor input type and raises the output voltage. This condition may not be obvious. Measure the HV (final plate voltage) and see if it is excessive. This may be caused by shorted C1 (original coaxial cap).
After unplugging the power supply, wait a few minutes, then short the HV and LV to ground. C1 can be disconnected and tested for a short circuit. If the original C1 is reused, remove the alternate C1 from the PCB.
Relay
The relay is the only significant modification in SB-1. The On/Off switch in the radio is NO LONGER AVAILABLE (unobtainium). Connecting the relay will prolong the life of the existing switch, which now only carries current to the relay coil. This requires minor rewiring under the PS chassis and is fully described in the mod. Refer to the original and post-mod schematics to understand the change.
Update 2015-12
Link to Schematics: Original PS, Sb-1 PCB, 516F-2 with Sb-1 Installed Write to me if you have any difficulty with the download and I will email the pages.
2. PCB Assembly
Consult the packing slip included with the kit. Verify all components are included.
3. Chassis Preparation
The following steps remove the unused components from the chassis. Determine which apply if you are NOT installing the full modification. Refer to the original schematic to identify component reference designators. The TB designators are not original, they are used as an aid in performing the chassis wiring.
The following photo contains reference designators for various terminals which are not identified in the schematic. These references are used to aid in the wiring list provided below.
All AC wiring, with the exception of the relay connections, should be complete before proceeding with the PCB installation.
There is an issue with the line cord clamp. The clamp comes in 2 sizes: too big and too small. The clamp which fits the cable is does not fit the hole in the chassis and the clamp which fits the hole is a bit to large for the cable. The solution is to wrap a few turns of electrical tape around the cord and then install the clamp. Heat shrink (maybe 2 or 3 levels) also works.
Effective Feb 1, 2015 the kit includes 2 pieces of heat shrink which should be cut to about 0.75" long and placed over the line cord where the clamp is located. These should be heated and shrunk. Do the smaller first, then the larger over the top of the first.
4. Unused Filament Windings
For AC wiring, see the schematic and photos. Some variation in wiring has been observed. The new schematic depicts the desired wiring with the AC high side of the line going directly to the fuse.
There have been some concerns expressed regarding the use of the filament windings to "buck" the primary. In particular the isolation voltage of the filament windings. In the tube version, the filaments operate with the full rectified voltage applied (800V or 300V). The winding insulation must withstand this high voltage and has for MANY years. Therefore, using the filament winding with 110VAC is much lower voltage than the original circuit. 2015-01.
NOTE - when wiring the filaments to the AC line and when wiring T1 to the PCB, it may be necessary to use the tube socket pins as an intermediate tie point or add extensions to the leads with a soldered splice and heat shrink tubing. Do NOT install the tubes.
5. Installing the PCB in the chassis
6. Bleeder Resistors
Depending on how much stripping of old wiring was done, you may have removed the wires leading to the bleeder resistors located in the perforated enclosure located on the top side of the chassis. These resistor are necessary and there is no change to the bleeders when performing this mod.
The HV DC has R4 & R5 (each 25K) in series to Gnd.
The LV DC has R6 (25K) to Gnd.
The original wiring instructions were intended to reconnect these resistors without adding specific wires. They were connected "for free" when hooking the PCB to the chassis.
As noted on the SB-1 schematic, R4,5,6 are not shown as they are not part of the PCB.
Wiring To-From Chart (With "Buck Mode" Filament Connections)
In the following table, the pin labels refer to PCB version C6 and C7 which had nomenclature changes to be more descriptive of the signal or voltage. Prior version pin are enclosed in brackets: [P123].