Converting the Collins 516F-2 Power Supply to Solid State

By John May, K6MAY

This article describes how to convert the 516F-2 to solid state. The main advantages of the conversion are the removal of heat from the 516F-2 and to prevent tube arc over. The 516F-2's black power transformer absorbs quite a bit of heat from the rectifier tubes. Extending the life of this transformer is well worth the effort.

Collins engineers recommended solid-state conversion in SIL 1-76 (available on the CCA Web site - www.collinsradio.org). While this is not an official service bulletin; it does show their concern with tube arc-over. It's general believed that Collins had a solid-state version of the 516F-2 in development, but was never released.

Another advantage is the reduction in filament current by removing the two rectifier tubes.

There has been quite a bit of controversy on modifying the 516F-2. Some believe that the conversion will allow a B+ on the plates before the filaments are sufficiently warm. The rectifier tubes in the 516F-2 come to life (producing plate voltage) well before the tubes in the KWM-2 reach operating temperature. In Addition, the 6146s are biased to cutoff at power-up, so no electron emission will take place until the PTT line is closed. There has also been many KWM-2's power by a Heath HP-23 solid-state supply for years. In any case, hundreds of owners have converted their 516F-2 with great success.

There are several recommendations to perform this conversion in addition to replacing the two rectifier tubes with some solid state equivalent. First, there is a transient suppressor that should be placed across the AC line input. Next, there is a 25 watt resistor to reduce the increased output voltage caused by the conversion. Then, there is a solid-state diode replacement for the selenium diode used in the bias supply circuit. Finally, there are two diodes to eliminate the power on slamming of the S-meter. Below is a parts list for the components needed for conversion.

Parts List

12	1Kv @ 1 Amp diodes (1N4007 or equivalent)
1	200 ohm 25 watt resistor
1	MOV Z130LA20A (or equivalent)
1	Diode 1N5408 (or equivalent)
2	8 pin octal tube bases
2	Diodes (1N4007 or equivalent)

Peter W. Dahl Co. Inc. makes a 5l6F-2 solid-state conversion kit (see figure 1). The current price is $34.95. It contains all of the above parts. In addition, the 5U4 and 5R4 solid-state replacements (octal plugs with solid state rectifiers) are already assembled. The kit is available from:

Peter W. Dahl Co. Inc.
5869 Waycross Avenue
El Paso, TX 79924
TEL: 915-751-2300
FAX: 915-751-0768
EMAIL: pwdco@pwdahl.com
Peter W. Dahl Co.

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Figure 1 - The Peter Dahl Conversion Kit

1). Install three diodes in series from pin #4 (anode of diodes) to pin #8 (cathode of diodes) of eight pin octal plug. See diagram 1.

2). Install three diodes in series from pin #6 (anode of diodes) to pin #8 (cathode of diodes) of eight pin octal plug. See diagram 1.

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Figure 2 - Tube replacements

3). Repeat steps one and two to make a second octal plug.

4). Remove the blue wire from pin #2 on V2 (5U4), and solder it to pin #1 on V1 (5R4). Pin #1 of the 5R4 is not used by the 5R4 or 516F-2. It will be used as a tie point for the dropping resistor.

5). Solder one end of the dropping resistor to pin #2 on V2 (5U4), and the other end to pin #1 on V1 (5R4). The typical value for the dropping resistor is 200 Ohm, 25W.

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Figure 3 - The Unaltered 516F-2 Power Supply

6). Connect the MOV transient suppressor, Z130LA20A, across the transformer primary. Use one side of the fuse, (Ring Section, NOT tip), and rear tie-point mounting strip (the one with the two black wires on it). The Metal Oxide Arrestor (MOV) transient suppressor is the one that looks like a small blue disc ceramic capacitor. This will protect the transformer primary from line voltage surges.

7). Replace the Selenium bias rectifier, CR1, with the Silicon diode, 1N5408, be sure to observe the correct polarity.

8). Plug the solid-state replacements for the 5U4 and 5R4 into their respective sockets.

9). Attach the meter protector, (two 1N4007 diodes back-to-back in heat shrink tubing), directly across the meter studs in the transceiver (KWM-2) or transmitter (32S-1/3), whichever may be the case. This protects the meter from slamming against the pin when first turned on. Leave any capacitor that may be connected (shunt) across the meter studs.

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Figure 4 - Meter Protection Circuit

10). Check all of your wiring and make sure the modifications have been properly installed before applying power.

11). Connect all cables and switch power on. Adjust R-9 bias potentiometer (right rear of the supply) for proper static current on the 6146's, (Approximately 40-50 Ma).

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Figure 5 - The Modified 516F-2 Power Supply