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For ha 11 e ry p or ta hie. m o hi I e a n d e m e rge n cy tigs, FM a n d A M.

is a description of design methods, L circuits, and components for homebrew generation of up to 5W (input) on 6 meters, for use with FM or AM, using reasonable cost transistors. A Vi to %W output is obtained from a crystal oscillator, followed by a parallel connected pair of Motorola HEP 75 transistors. These list for $2.95 amateur net, so you can see the truth of the low-cost mention.

The output can be pushed to equal that of the famous Gonset Communicator series, and nothing stops you from adding a couple more 75% using the described methods, for a 1OW rig.

The actual specs furnished say "total dissipation, 3 watts7\ThaCs for each transistor! You're out of the dry cell class then, but the Globe Co. has remarkable non-spill-able lead oxide storage batteries that wili surprise you, for portable and emergency work. So here are the details.

The Motorola HEP 75

In a box of goodies recently received from Motorola were some HEP 75 transistors which are the HEP iow cost version of the famous 2N3866, the solid state "Little

Five Walter*' for VHF and up into UHF. The real test was soon applied by soldering one in on 432—450 MHz in the place of a 2N3S66, and sure enough it showed up equally well. Since that day I have used them for added power in a variety of places

from 50 to 450 and they have all worked like the 2N3866, so here we go with details of how to add a 5W amplifier to your present 6 meter FM or AM solid state portable rig.

The One Watt Crystal Oscillator

Time was, in the good old tube days, you could run a lot of power out of a crystal controlled oscillator. The Taylor Tube Co. once advertised a crystal circuit, using exactly two tubes (Taylor, of course) that ran one KW (one kilowatt) de input to the final. CW that was. These days control crystal manufacturers seem very reluctant to say just how much milliwattage you can run through their thin little pieces of quartz. So, unless or until they come up with a definite figure beyond ''two or three milliwatts," we're on our own for awhiie.

It's ail very well for them to say "a couple of milliwatts" but if you pursue this policy down the line, and up in frequency, you can end up with a lot more transistors, amplifier stages, coils, and other components, than you originally planned on, as well as having spent more time, dollars, and cerebration than absolutely needed. Let's see what can be done to push the power per stage a little with these $2.95 devices with their 3W dissipation figure.

The schematic (Fig. 1) shows my favorite crystal oscillator starting out in the 1970 decade which runs one of Ihese - the lively, always ready to go - HEP 75-2N3866, There is a slight difference in the specs on the HEP 75 and the RCA 2N3866, this latter rated at 55 V and the former 20V. So for an AM rig watch out for that collector rating under modulation which can double the battery do voltages.

Recently, needing maximum power in a minimum package (always an interesting idea!) 1 kept pushing the 50 MHz oscillator power up and up until there was over a watt going into it and over l/2W coming out, which was driving the final in great style. Remembering the old trick of putting a pilot light bulb in series with the crystal, I soldered in a No. 48 bulb, as can be seen in Fig. 1, and sure enough, it lit up. Just a dull red glow, but checking with the "Amateur's milliwatt-meter" 1 found between 10 and 25 mW, depending on the tuning and output loading, as well as the battery voltage. This can also tell you interesting things about the oscillator such as how much of the generated power is being devoted to feedback and how much to the next stage.

Just how much power can you run through these VHF crystals? Recalling those not-so-long-ago (the late 1950's) tube days when over 100V and 20 mils to the plate of the oscillator brought on crystal instability, 1 pushed the oscillator under test still further, first making sure 1 was not using one of my favorite crystals. The oscillalor output came up to at 50.2 MHz, and the rf showing in the bulb in series with the crystal indicated about 20 mW. So far, no frequency shifts, noise, power jumps, or other noxious conditions have shown up. You can leave the crystal current indicator in or not, as you please. 1 checked the output with the bulb in and out and you can just see the difference, of some \ 5 mW out of perhaps 500 or so.

I just checked once again on the stability by listening to the carrier on my lab receiver which has a reasonably narrow bandwidth, and everything sounds fine. A good, solid "plunk" is heard when the oscillator is tuned in from one side, using LI and CI of Fig. 1, and an even, gradual climb on the other.

Incidentally, the coil being used just now is one of those tiny Piconic Co. jobs, the BK121K713Y1, less than 1.8th in. thick, so it's evident that you can pack the whole oscillator down to a real small size,

The emitter circuit as shown allows you to choose the power and current you want, and then put in a single resistor of the value found. The power control with R1 is very smooth as it should be. Check the output coupling very carefully when the oscillator is running and loaded with the amplifier input, because it is easily possible to overload it and keep it from starting up, even though it is a very good oscillator.

That about winds up the oscillator details, It is quite easy to assemble, and is not critical or touchy at any point.

The RF Power Amplifier

With the crystal oscillator bowling along nicely at V2 to output what will the amplifier do? The schematic, Fig. 2, shows the circuit, which runs smooth as silk and started off with a watt and a half output right away. The layout is shown in Fig. 3, After a number of tries in paralleling the

30h2

Layout Transistor C1972

Fig. J. Pictoriai view of the osciiiator schematic. For tuneup purposes, insert a No. 48 bu/b at point "X" in the crystal lead. The resistor connected from the base to +{10—14V) should be 4.7K. LI is 10 T No. 22lAi} diameter with the tap at 4T from the coiJector end.

HEP 75 transistors, with wires, soldering to the cans, etc., - not all successful I must admit, with some trouble from overheating when soldering the cans onto the relatively heavy copper strap of LI I took a little time to work up a mechanical paralleling holder which did an excellent job immediately and can be modified to hold not only m two transistors but three or even four. This simple little plank is shown in Fig, 4 and is made of copper clad stock, if you want to

be rea! fancy and obtain better heatsinking at the same time, use a piece of copper of some thickness, such as 1/8 in, J leat is a bulk effect and is conducted away faster by a thicker piece of metal. Notice the machine screws tapped into the copper clad, which allows insertion of the transistors after soldering to the copper strap ot LI, f his avoids excessive heat on these devices which, even though made of silicon and able to stand a certain amount of soldering, lm beginning to think do not really appreciate such treatment. In fact, Fm going to keep my iron away from them in the future. After all, that little plank shown in Fig, 4 can easily be skinned down to very small size if needed for higher frequency. As mentioned, you could easily put three, or even four in the circuit. I started out with a pot in each emitter circuit but found nothing critical there either, so I don't think it is necessary to have adjustments for each emitter, although it is always interesting during tuneup to have a few more knobs to twirl

The collector circuit is well tapped down on LI, as you can see, and has always behaved perfectly, tuning a! very close to the same place on the 100 pF variable capacitor C5, of Fig. 2, The combination of a copper strap inductance, the groundplane, the shield wall, and the low-impedance collector tap all make for a good Q, which shows up in the good handling of the resonance curve of LI,

The output circuit is the usual series capacitor, also tapped down on the inductance LI, and is well able to variably load both tesl bulbs and 50cables.

After you get the breadboard amplifier running properly in the size shown, you could think about installing it in a niinibox. For instance, substitute a much smaller coil

450 Mhz Watt Booster Schematic

U-0 TURNS in. COPPER STRAP, 3/4 in. 0.0.f 3-1/2 in. LONG.

Fig. 2, Schematic of the 5W amplifier, The rfc should be approximately 7-10 flH. C6 is 1000 pF disc ceramic, Q1 and Q2 are HEP 75's.

for LI , which is the largest component, being sure to check it for output power when you do, and you could put in a Johnson type M variable which is only 5/8ths by % in. in size, plus a fixed capacitor as needed. And test them first on the breadboard as shown!

Tuning Up this should include voltage tests, current, frequency checks, and output. Hour after hour get used up on the bench with this sort of work, but it's fun and if it also savesyou time, well, that s fine with me,

1 often think having been in "radio" for over half a century now, that if I have trouble tuning up these little beasties. what will the beginner do+> Well, if he reads this he can at least overcome the troubles I found,

! he first thing in tuning up is to get some drive into the amplifier base and start building up current from that. Actually, there are two coupling capacitors shown, and you really only need one. t hese are C2 of Fig. 1, and CI of Fig. 3, which are seen to be in series when you connect the oscillator to Lhe amplifier. If you leave them on two separate planks this is handy sometimes for cable matching* but if you mount these units on one baseboard you only need one coupling capacitor.

There being no dc bias on the amplifier base you rely on the oscillator drive to turn on the amplifier, and there is plenty of drive there to do this. As soon as you begin to get collector current you start in on the main tuneup job, most of it being concerned with obtaining a good match for the collector circuit, a matched load, and checking for resonance in LI. Be very sure you are not tuned up on a harmonic. It's not too likely bul it can happen.

Build up the drive and collector current a little cautiously, using CI of Fig. 2 and working with Rl to adjust the current. Generally you will not be able to push (via drive and Rl) ihe current up to the full 350 mils, or perhaps 400, until everything is matched and tuned. You may notice a buildup and then a drop in rf output as you push the currcnt up, before you reach the happy condition of having everything going right. This is why you generally see a variable resistor in most of my emitter circuits, at least for breadboards.

The oscillator drive you need should also be adjusted with Rl of Fig. 1, along with the

Model 372

increase v^ur talk power without exceeding legai limits. The Mode! 372 Ciipreamp will keep your audio levels uniform for maximum efficiency of your transmitter. Compression level variable to meet your requirements.

PRICE ONLY $19.95

See your dealer or write: Barker & Williamson, Inc.

Canal Street, Bristol Pa. 19007

C1972 Transistor Transmitter Schematic

Fig. 3- Layout of the 5W solid state 6 meter amplifier. The rf decoupling network between the amp and +12 can consist of 4 ,001 disc ceramics and SOT No. 28 on a VzW resistor.

iff A3*

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DIY Battery Repair

DIY Battery Repair

You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.

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