ALS-1306 Vacuum relay modification

Transcription

1 ALS-1306 Vacuum relay modification This modification installs two vacuum relays in the amplifier to allow nearly silent QSK operation. NG7M first did the modification to his ALS-1300 with input from Tom, W8JI, and I adapted the modification for the ALS The major difference in the two amps for purposes of the modification is that the control board in the 1306 uses all surface mount devices while the 1300 uses through hole components. There are three parts to the modification: 1. Installing vacuum relays on the antenna relay board 2. Changing two electrolytic caps on the control board in the bias circuit 3. Replacing two resistors in the relay driver circuit Installing the vacuum relays The ALS-1306 uses two small Potter Brumfield relays for antenna switching and they're the only components mounted on the antenna relay board. These relays are flush mounted on the circuit board and due to the difficulty in removing them, I decided to just purchase a new relay circuit board from Ameritron (around $25) and make the changes to that board. I removed the relays and cleaned the holes on the board. This board is secured to the 1306 filter board with two screws (a bit different from the 1300) and has two plug-in connectors connecting it to the filter board. The only wire connected to the board is the antenna coax coming from the SWR detector board and it's easily unsoldered. It's a teflon cable, so unsoldering carefully will not damage the insulation. Illustration 1: The stock antenna relay board in the 1306

2 I used two Jennings RJ1-A vacuum relays (12 volt model) which can be a bit noisy if mounted directly on a board or chassis and I followed the lead of NG7M in using a mounting technique that prevents transfer of the relay noise to any hard surface. Max, NG7M, had a terrific idea in using a plastic electrical box for the structure involved in mounting the vacuum relays. The material is easy to work with and is easily cut using a thin cutoff wheel in a Dremel tool. I was originally going to just use large rubber grommets to mount the relays, but the only ones I could find were very hard. I ended up drilling the relay mounting holes out to 3/4 and obtained a couple of 11/16 x ½ x 3/32 soft O rings. When slipped over the threaded relay body, the O ring makes a fairly snug fit in the 3/4 hole. I then split the grommet with a utility knife and used the grommet halves as washers to hold the O ring in the hole. Here's how the mounting arrangement looks with the relays in place. Illustration 2: Vacuum relays mounted to the relay board. The blue plastic piece is mounted to the board using two 6-32 screws, a bit longer than the originals. In order to minimize relay contact noise, I used the braid from a small diameter teflon coax to connect the relays to the board. When soldering the braid, clamping the braid with a surgical clamp close to the end will prevent the wicking of solder into the braid.

3 Illustration 3: Braid used to connect the vacuum relay terminals to the relay board. Illustration 4: Relay board diagram. HD4 is labelled as HD2 on the board, and RL4 is labelled RL2. Note that the upper set of contacts on RL4 that connect to HD1 are not used in the amp according to W8JI and so can be deleted (the vacuum relays are SPDT). I added silicon diodes across the relay coils to reduce the effects of the collapsing field in the coils.

4 Changing the electrolytic caps in the bias circuit This should have been easy, but due to my unfamiliarity with the surface mount caps it turned out to be not so easy. The objective is to replace the two 47 MF electrolytics (C78 and C80) with 10 MF units. After making a mess of removing the first cap, I found that the best way to remove one is to cut the cap in half (vertical to the board), leaving the metal pieces in the base of the cap in place. Illustration 5: The two caps to be removed are adjacent to the "A" and "B" at the bottom of the photo. These are 47 MF electrolytics.

5 Illustration 6: The left-hand cap was soldered to the metal base of the original cap that was cut in half and removed. The right-hand cap required repair of a lifted land. Replacing two driver resistors The original driver transistor circuits had a 10 ohm resistor in the emitter lead and those had to be removed and the replaced with a zero ohm connection. I didn't have any zero ohm surface mount resistors of the right size, so just used a piece of wire to bridge the gap after removing the resistors. Illustration 7: The resistors removed are R68 and R78. Replace with zero ohm resistors or piece of wire.

6 Illustration 8: R68 and R78 replaced with wires. Conclusions This modification results in the ALS-1306 operating very quietly in QSK mode without the need of an external QSK unit. This assumes that your transceiver provides the necessary delay between PTT closure and the start of RF output power. In my case, my FT-1000MP Mk V has a fixed delay of 12 ms (even though the manual says 5 ms). If you use a new relay board as I did, saving the original, you can easily reverse the mod if you desire. Many thanks to Max, NG7M, and Tom, W8JI, for the original work on the ALS-1300 modification. 73, Floyd Sense K8AC West Jefferson, NC May 5, 2017