The Neat m Amplifier

A great pair of shoes for your HT or data radio.

Photo A. Tuning ir up to 35 watts, just like the specs promised!

Bill Richarz WA4VAF 10035 Little Creek Road Charlotte NC 28227

f you are using an HT or other low Lpower radio for packet, you may want to try your hand at building this Ten-Tec 2-Meter Amplifier Kit. Even if you're not using your HT for packet, you can take the ''scratch" oul of your Handi-Seratchy so everyone will hear you full quieting, and love you for it.

Recently I acquired one of those low power data radios from MFJ. It did a fine job of receiving packet, but with only 5 watls oul, ihere were too many Retry & There were some stations I could copy well, hut they were not hearing me. 1 needed a boost in power to eliminate the Re try s. Enter the Ten-Tec Kit. Ten-Tec, a well-known HF manufacturer, has a line of small kits in their new T-KIT Catalog. With an RF sensing TR Switch and 20 to 35 watts RF output, 1 decided this little baby would fill the need and stay within the budget. Most of the 2 meter amplifiers out there are expensive and usually include a receiver pre-amp, which of course adds to that cost. Ten-Tec holds the price of this kit down by eliminating the pre-amp. Since most of today's 2-meter transceivers arc quite sensitive, and the pre-amps sometimes only enhance any inter mod, 1 decided to do without a pre-amp and save the money. The kit costs $74 and also comes assembled (for the lazy) for around $120. Here's where you can save some bucks, and have all the fun of assembling it yourself.

I feel many hams who were not around during the Heathkil era really missed out on the fun of kit building,

44 73 Amateur Radio Today May 1996

To take a pile of parts, solder them on a PC board or chassis, and have the whole thing come to life...well, you can't imagine the feeling until you try it for yourself, After all, experimenting and building are an important part of ham radio,

Introduction

The T-KIT No. 1200 offers you the opportunity to construct, understand, and use an RF Power Amplifier for the 2-meter. The amplifier is designed

"You can take the iscratch9 out of your Handi-Scratchy.

for mobile, portable, and base station operation, providing over 30 watts of RF output, operating from 12-15 Volts DC. It comes with a detailed construction manual and all parts, including enclosure and hardware. Nothing extra to buy well, almost nothing; they do not include those little rolls of solder that Heathkil builders had come to expcct. So if you decide to build this kit, go out and buy a roil of 60/40 resin core solder, small diameter. Also, let me say here Ten-Tec does not project this Kit as ^Super-Easy/1 This is a VHP construction project and attention is required in soldering technique and pails placement. Don't be intimidated, though, This can be your first kit, with the help of an Flmer with some experience. You should be able to complete this kit in a single evening. Before you get started, I would suggest reading the complete manual to familiarize yourself with all the parts and terminology used in construction of

Photo A. Tuning ir up to 35 watts, just like the specs promised!

this kit. Also, you will need a few tools such as a 25-watt soldering iron, diagonal cutters, needlenose pliers, and a Phillips screwdriver,

Circuit description

Q i is a VHF RF power transistor op-crating in Class AB (Sec Fig 1), Bias is controlled by Q2, adjustable by 100-ohm trimmer R2, Q3 and its related components form an Rl--sensing circuit which energizes the T-R relay during transmit only. When the relay is not energized, the input is shunted to the output, bypassing the amplifier circuit. This arrangement not only makes the needed antenna connection for receiving. but also permits normal use of the transceiver when the amplifier is turned off.

C5 is adjusted to peak the input circuit at the base of Ql> and C6 peaks the output at QTs collector. L4 through L8 on the schematic diagram are striplnies designed into the circuit board itself. The amplifier may easily be modified for Class C operation, if desired.

Getting started

While the manual provides step-by-step instructions, there are no illustrations other than the circuit board layout and an exploded view of the final assembly (Fig. 2). You should check off each step as it is completed in the boxes provided in the manual. Also pay close attention to the orientation of the banded cathode ends on the diodes as they arc installed. The PC board is silk-screened with the component outlines, making it easy to position them correctly, All parts arc mounted on the top side of the PC hoard and soldered to the bottom, except for one transistor which is mounted on the bottom, so there is little chance for error. The one problem you might encounter is the winding of an RF coiL It consists of 12 turns of the supplied #16 enameled wire, close-wound on a standard 1/4-

inch drill bit.

The kit may be built for class AB or class C operation, making it suitable for FM, AFSK. AM, SSB. or CW operation. I would suggest building it for class AB. then modifying it for class C, which is what I did. I later cut the two jumpers, making it a class C amplifier for use with my 2-meter FM

packet station.

I had no problems mounting and soldering the components to the small board. On completion, it is a good idea to inspect the PC board for bridged solder joints, correct orientation of diodes and transistors, and correct selection of resistors and capacitors. Although satisfied that all parts were assembled correctly, I was a little hesitant in applying power for the first time. Ten-Tec gives no resistance measurements to check before the initial smoke test. I measured the resistance between ground and +DC connection and found it to be about K ohms. At least it wasn't a dead short. I hope they will add some resistance checks in later printings of their manual, to give the kit builder a bit more confidence before applying the voltage.

Final assembly and connection

The fully assembled PC board is mounted on the heatsink. End panels with ihe input and output connectors are also mounted to each end of the heatsink. Soldering the inpui and output capacitors C7 and CK to the BNC and SO-239 connectors complete the electrical connections, rhe power cable is run through a strain relief erommet, then locked into place,

Adjustments

If you buitd the amp for class AB operation you must make an ininal bias adjustment using your VOM This is clearly explained in the manual. It

5012 line

Ground + DC

5012 line

Fig. I. Schematic diagram*

you built it for Cass C only, then you may forget this adjustment. Connect a 50-ohm dummy load or 2-meter antenna to the SO-239 output connector through an RF wattmeter or SWR/ wattmeter. Connect your low-power HT or other low-powered transmitter (five watts or less) to the BNC input connector. With RF applied to the amplifier input, tune the input and output capacitors C5 and C6 for maximum output on your meter, I was able to obtain 35 watts out. That completes the tune-up. Mount Hie cover on the chassis and you're ready to enjoy contacts that will hear you just as well as you hear ibem.

Conclusion

The Ten-Tec manual contains a troubleshooting guide that you probably won't need, but it's there, just in case. Its 26 pages include a circuit description and schematic diagram. Ten-Tec also has a limited warranty and a phone number for technical assistance should you need it. The back cover of the manual shows the resistor color codes and bits of other useful information.

I found this kit quite easy to assemble and had no problems — the amplifier performed as advertised and was fun to build. It doesn't have a larse number of pans so it shouldn't overwhelm the new kit-builder. It completely solved my packet problem. It Should also give the HT user quite a boost for the buck: no more, "Well, you 're a little scratchy!" The only modification I would suggest is the addition of an ON-OFF switch. A Radio Shack™ illuminated switch mounted on the top side of the case will let you know when ifs switched in or out, and allow you to run mint mum power when high power is not required. Other than that, if you want to get your feet wet building a worthwhile project, 1 think you will enjov building and using this 2-meter amplifier as much as 1 did, and you too can say, 4\,.Oh yeah, 1

built thatr

You can get a free T-K1T Catalog by calling Ten"Tec al (423) 453-7172. T-KIT is a division of Ten-Tec Inc., 1185 Dolly Parlon Parkway, Sevierv illc TN 37862-3710. ""

Chassis

Heat Sink

PC Board

f ig, 2, Exploded view of the completed kit,

Input paid

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