Amplifiers

Commercial Amplifiers - 

HF (160m–10m & 80m–10m)

There have been many HF amplifiers in my shacks over the years, and they have been a combination of good value, utility, and fun. With one exception, all were used, and the homebrew ones had the added enjoyment of "tinker-factor" and were strong performers. Still, once I sprung for my first Alpha, a 76CA, reliability and headroom became the norm, and I haven't really looked back, but I haven't always achieved that goal either.  

After a partially built 4 x 811A amplifier (I ran out of funds, before building the power supply), and an ill-fated purchase of a Johnson Courier amplifier, which never did work, I purchased an Eldico SSB-1000 while in college. I had my Drake B-Line set up in our dorm room, and met a guy whose dad was a ham who had the Eldico for sale. I bought it for $250 and set it up in the dorm room, earning the coveted WAS (worked all stereos) award. Somehow, I got away with it for over a year. That amp introduced me to ceramic, external anode tubes, a pair of 4CX250Bs (until 2021, I still used a pair on 6M), which I got back to in the Alpha series of amplifiers, 10 years later.

In the interim, I sold the Eldico to buy tires for my car, and later picked up a Heathkit SB-200. I didn't have the 200 all that long, but a boyhood friend, WA3OYA, had built one back when we were still in high school, and I always liked it's compact size and reasonable price.

As I set up my first shack in our first house, the old Drake B-Line got a little help from a Heathkit SB-200. I had some experience with this amp at a friend's shack, and it was affordable for a new homeowner. The shack was pretty sparse with a tuner, antenna switch and a mic., headphones, and paddles. Soon to follow was my first tower, tribander, 2m yagis, and a 40m wire yagi and 160M dipole.

Then, in 1980, I got the tube compliment I had wanted for a long time, a pair of 3-500Zs, in the form of the Kenwood TL-922A. It had die-cast side panels with handles, a solid top (and other poor ventilation/cooling features that melted the solder in a tube pin within a couple weeks), but really looked the part and did a good job overall. It also had the advantage of 160M coverage, and despite some component failures, including a bandswitch wafer, it served me pretty well for 3 years. The Eldico, Heathkit, and Kenwood comprised my experience with HF amplifiers, prior to my string of Alphas.

The Alpha Era UNRIVALED IN THEIR DAY

The beginning of my series of Alpha amplifiers, the 76CA. It matched the TS-930S paint scheme, and was a true workhorse still in operation to this day at W4ACM, now converted to a pair of 3CX800s.

Alpha 76CA

 I don't remember where the ad appeared, but I came upon a one-year-old 76CA, that had been used as a test platform to "exercise (read, try to blow up)" antennas but was otherwise unused. I still remember receiving the package at work (it was cheaper to have packages shipped to a commercial address) and being sorely disappointed. Although in like-new condition, I hadn't yet embraced the simple clean lines of the Alphas. The Kenwood, with its die-case side panels and fold-out handles, made the Alpha look  too plain. The 76CA had the infamous "sticky paint" but it was still in perfect condition when I received it, with the look of gray suede, and it wasn't too long before I began to appreciate the flush meters, elegant vernier knobs, unique push buttons, T/R meter illumination color changes, and the fit and finish of the cabinet, chassis, and front panel. What was easy to get used to was the quiet operation, and willingness of the amplifier to make power, seemingly without effort. 

For those unfamiliar with the differences, the 76CA featured 3 x 8874s, and a hipersil transformer. It also included 160M as did the TL-922A which was a key band for me in those days, with the power restrictions removed, and nearly daily operation with a group on 1.858. With a simple dipole antenna at about 60 feet. the extra power helped especially in the winter months. Also, my contesting was hitting full stride, and the repeatable, smooth tuning and hour-after-hour power let me concentrate on operating. I had only a meter shunt and a couple of pilots lamps fail in the 9 years I owned the amplifier, which is still running strong at my cousin's QTH on the Eastern Shore of Virginia. The paint on the front panel finally turned more gooey than sticky, and rubbed off in places, but otherwise, the amp is still in great shape.

Alpha 78

A BROWN AMPLIFIER WITH BROADBAND TUNING?

YOU KNOW IT! 

I became interested in the Alpha 78, based on the solid foundation of the 76CA, and a desire to have quicker band changes, and quieter T/R operation, with the possibility of QSK. A friend, Bob, W4JNN and later K4JN (now SK), had one of these, and encouraged me that I'd get used to a two-tone brown amplifier, and he was so right. I now consider the 78 to be the most attractive amateur amplifier that I've owned. I had two of them, over a span of probably a dozen years. The first was in great shape, but was misrepresented by the seller, having 3 tired 8874s. It also had one noticeable ding in the front panel. I ran my spare tubes, and sold it later for $1,300, disclosing the weak tubes to the buyer. I met him many years later, and he told me it was still running (no surprise to me.) The second one was in collector-quality condition, and the tubes were also fresh. It had been a backup amp, and I drove to Baltimore and bought it out of the trunk of the owner's car. Although there are logistical problems with retrofitting the 78 with 3CX800s, that was what I should have done, in retrospect. The Alpha 89 that replaced it, although now basically solid and reliable, gave me many problems for a couple years, as described below.

The next series of problems were all centered on the PIN diode QSK board in the amplifier. It is an excellent performer, when it's right, but in my case, the receive diodes blew on three separate occasions. Although they are reasonably inexpensive ($12 each), they are somewhat difficult to replace, and each failure also shorted the drivers in my K3, and I reluctantly decided to ship it to RF Concepts for repair. To ship it, I needed to buy a box, and after the resulting repair, which included some post-production modifications to other problematic components, and over $600 later, I got less than a year's use before the next failure, including damage to the K3. That time (late 2012), I decided to take another approach. I built an outboard QSK box, based on the W7RY QSK driver board for the L-4/L-7, vacuum and reed relays. Luckily, the 89 worked perfectly on transmit, including bias switching and the expensive transmit PIN diodes were still fine. That allowed me to use the RELAY OUT from the amplifier to key the external box. With internal sound-deadening foam, and floating the relay on foam tape, and braid to connect to the coax connectors (added after this picture was taken), the operation is all but silent, and fast enough for QSK operation. I had an RJ-1 and also a suitable 21VAC transformer, so the entire project cost under $100. The cost for all the parts, including a new Gigavac GH-1 from MaxGain Systems, is just a couple bucks short of $200. I built a second one for the station at KP2M, owned and operated by longtime friend and CW Maestro, KT3Y, who experienced the same failures with his 89.

  The RF deck, as built by Jeff, WA8SAJ. He is a top gun Drake

  tech. these days. You can see  that Jeff was a Drake man,

  even back in the 1970s. Some of the labeling was damaged 

  when I got it, and I decided that the front panel could use

   paint and relabeling.