Install the components from left to right as looking at the front panel, with a couple of exceptions, such as the 10v fuse array and the large caps. This will permit sufficient room for tightening the screws of each item. Therefore, you'll start with the AC connector, then the fuses and other RFI protection devices, MOV, and the LED fault circuits. Then the main transformer (after removing 2 windings each way), the 12v transformer, all the large diodes, all the large capacitors, then the choke, L3 and other items, like the fan, etc. A word (the other exception) on the large caps. The clamp's tightening screw is rather hard to reach with a screw driver. The best approach to this little problem is to install C3 and its bracket first, then C2 and its bracket, then last, C1 and its bracket. This will allow to you get a small or stubby Phillips screw driver to tighten the first two caps; then you need a right angle type for the last one. Then install the heavy wires going to all three caps.

More details:

Here's more pictures to help you with this project. After the holes are drilled, clean up the areas that will have ground connections, then mask over them just before the painting of the box. Afterward you can peel the mask off for a clean-looking ground spot. For the AC input area you can get started on mounting the fuses and input filter. Sometimes it helps to make up little "sub-assys" of a few components, then install them. One example is the MOVE on the right picture.

As a reminder, the power connector was later moved towards the rear.

It's a good idea to apply heat sink goop on the bridge for the 12 volt section as well.

These show the earlier built with the plug towards the front. It made a "snarly" closed spaced with several wires. The move towards the rear somewhat corrected this issue.

Most RFI issues happen at high-powered transmitter sites. For this project involved surviving at a FM broadcast site. That's were the line's toroid filters helped. They were "tuned" for the FM-broadcast band by experimenting with the amount of turns of wire and checking them with a tracking generator for the 88-108 MHz area.

For the "L" brackets that hold the (insulated) heat sink for half of the 10v bridge, you can get them at the local hardware store. However, being "cheap" you should smooth out the surfaces/edges that will come in contact with the mica insulators, so any sharp points don't punch through and short the bridge to ground. Just grind, file and polish any burrs off.

When you install the mica insulators arrange the nylon screws as the pictures show.

This is what it will look like when it's tighten down to the main chassis. Spot welding the 10-32 nuts on the lower part of the "L" bracket is optional. It makes positioning the (hard to reach) nuts easy, however with a steady hand you don't need to. The heat sink will dissipate most of the heat generated by the diodes. The other side of the bridge is mounted directly (and electrically) to the main chassis bottom and should sink as well. During long (key-up) current consumption periods this may not be sufficient sinking to stay within safe operating specs. Therefore, a fan to circulate the air inside the unit is needed. Running the fan continuously increases fan wear and brings in excessive dust. So is so typical on most computer and communication equipment, however the Author thought of a way to increase the lifetime of the fan. By using a temperature demand (thermo switch) it's only on during those long demands. Bimetal switches are used; two of them for redundancy for increase reliability. For more information on OEM switches, click HERE . The right picture just shows the 12v bridge mounting.

You need to brush off any paint for the two ground points. For the MOV/AC area it might be a little easier if you use a nut between the lugs. In the event you need to replace the MOVs the other lug (green wire) won't become loose.

For the high current (10v) wires, however it's recommended to tighten down both lugs without a nut in between for maximum connection. It's unlikely you'll need to remove this wires in the future.

As mentioned before, the exception (left to right installation) will be the 10v fuse array, since it's a tight fit, then the choke. Speaking of the fuse array, perhaps some words on this subject. Old school 1970's the micor used the "B01" or "B02" (type AGU) large, fuse for the large (red) lead powering the PA section. For the high power radios this was usually a 40 amp value for the (single) fuse. While this seemed to work for both (intermittent duty) mobile and (continuous duty) base/repeater station, all the current runs through a rather small portion of the fuses's surface, only where it touches the contact area for the fuse holder. This was a "butt" connection, where-is the holder's contact would press against each end of the fuse. The Author came up with possibly a better way by paralleling four fuses with an array (holder). This distribute's the current through four sets of contacts (clip type). Another (small) advantage is easier to obtain replacement fuses, since 3AG or MDLs are common in most stores. The former (AGU) is more difficult to obtain. The cost is about the same, as well. The original selection was to use four 10 amp fuses, providing a 40 amp protection. Since the (transmitter PA) load only runs around 22 amps, it was later decided to lower that value to 32 amps. Four 8 amp fuses provides this nicely. Also, to provide a little extra protection against nuisance (and expensive trips) fuse blowing from (typical) hill-top power surges, it was decided to spec all the fuses (not just this section) for slow-blow (MDL type). The picture shows an eight position holder, which was an exceptable substitution from Hosfelt Electronics source. In this event this holder replaces the (single position) holder for the fan, per the parts list. The images show the events to install such an array.

One minor note on the choke has terminals with a number 12 hole, however the 10-32 screws and ring lugs specified work fine. Speaking of this choke, it's a 1 mH, 30 amp and hard to get a good price, and most distributors have a minimum as well. If you can shop around, but need the specifications click on the document you wish:

The Alternative source in PDF format

The right picture shows L1. A option is to carefully drill out the holes to 1/4" and use a nut-bolt arraignment. Be real careful; the drill bit can "grab" the lug, pulling it out of position and destroying the expensive choke.

 

 

 

 

 

 

 

The main transformer was designed for a UPS or similar device. In order to get the (nice) lower, 10 volt output you will need to remove several windings on the secondary side. It's a little tough for the first one, but with a little practice it's not too bad. Start with cutting the first few windings with dykes and remove each one.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

approximately 7 windings on the outside layer are left in place for 11 to 11 1/2 volts AC secondary with no load. If in doubt leave an extra winding, power up the transformer and check the voltage. After the last windings are removed, bend the remaining ends down at a 90* angle to the housing. It will look like this when you are done with this task.

 

 

 

 

 

 

 

For the 12 volt section a new type of circuit was found and implemented in serial numbers 2~4. The major change of the is circuit is a LM-338, TO-3 type 3-pin voltage regulator. The author found Jameco Electronics has them for about $5.70 with a part number of 23835CB. Start with wiring up the sub-assy components for the section. Here's one ready for installation.

 

 

 

 

 

 

Some close-up views of this sub-assy.

 

 

 

 

 

 

 

 

 

 

 

 

Drill 4 holes in the heat sink, two for mounting this sub-assy on, and the other for mounting the entire unit on the main chassis. Here's a couple made up ready for installation.

 

 

 

 

 

 

 

 

 

 

 

 

A word about IC orientation. The heat sink is factory made with two "units", then were broken up in half. Because of the (offset) holes for the IC's leads some of the heat sinks have the holes going to the right, or left. For example, in serial number 2 is opposite of these, for serial numbers 3 and 4. It won't damage the IC, but, of course will not work if you have the two wires the wrong way. It's good to check the IC's data sheet, here available in PDF format, by clicking HERE .

 

 

 

 

 

 

Use some heat shrink around the "hot" leads for additional protection of accidental short circuit, while probing around.

 

 

 

 

 

 

 

 

 

 

Here's what the installed sub-assy should look like on the main chassis. Note that this is serial 2, which did not use the small capacitor clamps; instead, the caps were glued. Speaking of the large capacitors, occasionally Mouser, or any other vender for that matter, may be out or discontinued the first selected large capacitors given in the Parts List . Also most venders require a ridiculous minimum amount (I.e. 10 of them), forcing you to find a substitute/ single order item. Therefore, an additional chart/list may help. In fact, serial number 3 and 4 has (smaller sizes) substituted caps in the 2 1/2" diameter, therefore, a different part number for the clamps had to be ordered as well. The larger, 3" one is still the same as all of them. The chassis size and component layout was designed to accommodate variables such as this.

 

 

 

 

 

 

 

 

 

 

 

 

Here's a peek behind the terminal block for the 12 v section. The wires come through the front chassis and are soldered directly to the top section of each terminal. The bottom section still has its screw for the wire lugs of the load equipment. Another note is these pictures reveal straight-blade screw heads. All the screws were upgraded to Phillips type to help with screwdriver operation.

 

 

 

 

 

 

 

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