Heathkit SB-200 600 Watt Amplifier

SB-200 Amplifier
Heathkit SB-200 Linear Amplifier – Refurbished

I bought a used Heathkit SB-200 linear amplifier way back around the year 2000. I didn’t need it at that time because I had a Heathkit SB-220 amplifier that was a functioning piece of equipment.

The SB-200 has been sitting in my basement getting older and gathering dust ever since. Just this last month I made the effort to restore the SB-200 to its old glory.

Heathkit sold thousands of SB-200 and SB-220 amplifiers. Since Heathkit went out of business, an entire cottage industry appeared supporting these popular amplifiers. Power supplies, QSK modification designs, added band designs, and parasitic oscillation suppression schemes  are available.

The SB-200 uses a pair of 572B triodes in grounded grid configuration to deliver 500 to 600 Watts CW output. For SSB peak envelope power (PEP) output, it will run up to 1,000 Watts out. One downside is that the SB-200 only covers the old, standard five frequency bands of 80 to 10 meters, without 30, 17, and 12 meter operation.

There is one more negative point. To key the SB-200 amplifier, your transceiver has to be able to switch  up to 150 VDC. Most modern transceivers can switch amplifier keying voltages of only about 12 VDC. Without an interposing relay, the high DC voltages will absolutely FRY your pet radio. HamGadgets has a Universal Keying Adapter that will solve this problem. You can see this adapter in the picture at the end of this article. It is the little box on top of the amp, next to the AT-500 antenna tuner.

High quality kits from Harbach Electronics were used in refurbishing the SB-200.  For about $115.00 I got the combination power-supply board and kit, plus the soft-start board and kit that limits the in-rush current into the power transformer. The last sentence in the power supply instructions tells you that you will never need another power supply for your SB-200. I believe them. Harbach does a great job.

Last Wednesday morning I put the amplifier on the air in a seventy-five meter QSO with some folks in Illinois, New York, and Pennsylvania. The frequency was 3720 KHz, and I was there at 5:00 AM because I had been told that one of our NFARL re-located club members, David Sturm, would be on frequency. He now lives in Ecuador and is operating with the call HC5/WB4OZM. He told me earlier, confidentially, that his new Ecuador callsign will be HC5DX. The guys on frequency told me that I was way too early for David.

The amplifier was tuned and loaded to 6oo Watts out at that frequency, and I was probably hitting close to 1,000 Watts PEP on SSB. I was proud that my hard work was paying off. Fortunately, my Alpha-Delta parallel dipole antenna has a VSWR of 1.3:1 at that frequency. How lucky can you get.

This afternoon, my eyes fell on an Icom AT-500 fully automatic, 500 Watt antenna tuner that covers the

SB-200 Amplifier and AT-500 Automatic Tuner

ham bands from 160 meters through 10 meters, including the WARC bands. I have had this tuner for over twenty years after buying it used at HRO. I wondered if I could use this auto-tuner with my SB-200 to cover more bandwidth on some of the bands I operate.

This was one of those “DUH!” moments. You see, the auto-tuner can handle up to about a 3:1 mismatch. The pi-network output of the amplifier can probably handle a similar mismatch. I tested the amp on forty meters at the bottom of the band (7003 KHz) where the mismatch on my dipole was measured 3.65:1. It handled the mismatch well. I only ran the power up to 400 Watts to be conservative.

There is no use for the auto tuner with a pi-network output tube amplifier. If I want to handle larger mismatches, I will need a high-power transmatch.

I now have a nice 500 Watt linear amplifier for most of the ham bands.  SB-200’s  can be bought on the used market for $200 to $800 dollars depending on the condition of the amplifier and its tubes. New tubes will cost over $150 for a matched pair. Pretty much all of the tubes for these older amplifiers are made in China.

Working on high power amplifiers is not for everyone. My training on working on high-voltage apparatus came when I worked at an AM/FM/TV broadcast station as a transmitter engineer. You really need to understand the dangers involved, even in a small amplifier where the high voltage is 2,400 VDC. It can kill you.

73, and see you in the contest.


A Tale of Two Baluns


Several years ago, I spent some time reading Larry Sevick’s book, Transmission Line Transformers, because I was curious about balun  (Balanced to Unbalanced matching) transformers and how they worked. I don’t remember all the fine details, but I did wind several small baluns for use around the shack. Some of these were to match a Beverage low-band receive antenna.

Home Brew 9:1 Balun Using Two Toroid Cores

One balun was to match a 450 Ohm ladder-line fed, 135 ft dipole antenna that was reputed to work on all HF bands. I had to use my Icom’s antenna tuner to use the antenna. It worked just fine. The balun was used between the Icom’s output, and the ladder line input, and had to handle at least 100 watts CW.

Now, I am putting together a travel kit of my KX3 transceiver, keys/microphone, power supply, and antenna system. I intend to use a light weight, portable Off Center Fed Dipole  (OCFD), and the design requires a balun to match the coaxial feed line.

That’s where my QRP 9:1 Balun from Palomar Engineers comes into play. Palomar Engineers has a comprehensive line of baluns,  some already in enclosures ready to be installed into an antenna system.

Palomar Engineers QRP 9:1 Balun On Test Antenna Support

I compared the Home Brew 9:1 balun and the Palomar QRP 9:1 balun using an MFJ 225 Antenna Analyzer to measure each balun installed in the same antenna.

The characteristics, surprisingly, are different.

Home Brew 9:1 Balun Analysis








Palomar Engineers QRP 9:1 Balun Analysis








So, what’s going on? As you can see from the photos of the two devices, there are substantial differences in the construction. The Home Brew Balun uses two toroidal cores, and the Palomar Engineers uses only one ferrite core ( not toroidal). All the same, the analyses should be very close.

There are similar bumps in the SWR in each graph. One problem may be that the Home Brew balun was on the test rig for about three weeks in wind and rain. There was substantial water in the device when I opened it. The Home Brew balun probably had more loss compared to the Palomar device which had not undergone the rigors of the weather.

The Home Brew balun was wound with Radio Shack speaker cord, similar to zip cord. One article warns that the speaker wire has more loss than enameled transformer wire. I may have verified this information.

Lessons learned.

  1. Mechanical integrity is necessary in construction. Even though the Home Brew device was locked up tight in a water proof enclosure, the moisture leaked in through small openings where the cable connectors are mounted. A silicon sealant could have been used to keep moisture out.
  2. In procuring parts for the enclosure for the Palomar QRP balun, I decided on a BNC connector for the coaxial unbalanced connection, and binding posts for the separate wires on the balanced side of the balun. I got cheap binding posts from China, and regret that decision. They are really bad.

One of the best discoveries is that the Elecraft KX3 has an excellent Antenna Tuning Unit. If you look at the VSWR levels on each of the ham bands, most are above 3:1, and some like 30 meters are not within reason for most manufacturers’ internal tuning units.

The KX3 handles the mismatches without a problem.

I am considering a differently dimensioned Off Center Fed Dipole, this time using one-third of the antenna length for the short end, and two-thirds for the long end. My current test antenna uses 25% for the short end, and 75% for the long part, with the total length being 66 feet. Maybe I can get the matching transformer requirement down to at least a 4:1. Maybe I can find a truly water proof enclosure, too.


Jeff, N1KDO suggested that I use a 450 Ohm carbon resistor on the output of the baluns to represent a 450 Ohm impedance to establish a baseline for reference. Having a reference before measuring other parameters can be beneficial when looking at the system performance. I used a 470 Ohm resistor because I had several, and no 450 Ohm resistors. This is just fine, because 470 divided by 9 is equal to 52 Ohms, which is darn close to the coxial cable impedance of 50 Ohms.

The graphs show the impedance, |Z| and the VSWR fairly level across the 2 to 30 MHz passband. This confirms that the winding ratios are approximately correct. Remember that we are looking at the impedance on the input of the baluns, and it should be very close to 50 Ohms. This means that the balun has transformed the approximately 450 Ohm antenna impedance to one-ninth to match the coaxial cable.

Both graphs show a gap between VSWR and Impedance, but that is not relevant because they are plotted on different scales. What is important is that neither set of graphs are totally level. To me this indicates some minor problems. I found some corrosion in the Home Brew balun, and that may explain the wavering relationship in its VSWR and Impedance (|Z|) traces. Also, the flaky binding posts in the enclosure that holds the Palomar device can be contributing to what I think is an instability in the values across the pass band. It pays to be careful when planning and constructing a project.

Home Brew 9:1 Balun Terminated With 470 Ohm Carbon Resistor
Palomar QRP 9:1 Balun Terminated With 470 Ohm Resistor










Field Day – My Opinion

“If winning were not important, why keep score?”

Antenna At NFARL Field Day 2000
An Antenna At NFARL Field Day 2000

Field Day is an opportunity for individuals and clubs to test their ability to operate in emergency conditions. That’s why we locate in parks and fields, powering our stations using emergency generators. We practice for the emergency we hope will never come.

There are always people who want a big picnic. Some of us like to operate radios, and welcome the contest portion of Field Day. The idea that Field Day is meant to be a contest is absolutely correct. If all we wanted was a picnic, we wouldn’t need any radios. That’s not were I want to be.

We are HAM RADIO OPERATORS, and our public duty and vocation is to OPERATE RADIOS. If I am going to spend hours operating a radio on a hot June afternoon, sacrifice a night’s sleep, and stagger around drunkenly on a hot June Sunday dismantling the site, I want it to be worth something. Field Day is based on operating, hence it’s a contest.

Making radio  contacts is a big thing. One problem is that we need people to make those contacts.

Every year there is a crunch to find operators to work both SSB and CW. We have members who do not operate their radios very much. Maybe that’s because a high percentage of our members do not have General Class HF band privileges. That means that we have to work extra hard during the regular year getting members to upgrade, and become honest-to-goodness hams by getting on the HF bands. Repeaters are OK, but they are a nice-to-have thing for club members.

The best radio operating skills are forged on the HF bands in contests. Contests may seem to be a bit cheesy with operators trading only signal reports and some other piece of information. They are much more. Contests teach you how to operate in crowded and noisy conditions, and causes both phone and CW ops to improve their operating skills to compete.

We can’t solve these problems in time for the 2017 Field Day. We will have to go with those operators we have.

I will spend Field Day with my home club, the North Fulton Amateur Radio League. My loyalty lies there.  The last two Field Days, we competed in the 3A Category, and finished #1 in the nation for those two years. This is a source of great pride for the entire club.

Anything less than our past efforts would be a disappointment.


My Elecraft KX3 And The DX Contest

Elecraft KX3 QRP Radio
Elecraft KX3 QRP Radio

For some reason I missed the notices that the ARRL CW International DX contest was scheduled for this weekend. On Saturday afternoon while putting a recently acquired Elecraft KX3 on the air, I discovered the contest was in progress. I was interested to see just what I could do in an International DX contest with only 5 watts.

I got the KX3 from a local amateur, and was not anticipating any problems getting the little radio on the air. There were no problems with the rig, except operator problems.

I could not get the Antenna Tuning Unit (ATU) working. After a couple of hours messing with menus and reading manuals, I made a call to the previous owner. His return call came a couple of hours later, and his advice made the problem disappear.

You see, the KX3 is a QRP radio and mine has the optional ATU. Elecraft has a matching 100 watt amplifier (KXPA100) that will give the rig a boost. The problem is that if the amp has an ATU, you need to disable the ATU in the KX3. The previous owner had the KXPA100 with its ATU, and the option had been disabled in the KX3. After an adjustment in the configuration menu, all was wonderful

The KX3 is one sweet, little radio. The receiver gives big-time performance even without the optional crystal roofing filters because the DSP does a good job of filtering, too.  The KX3 may have the best receiver I have ever had. My Kenwood TS-2000 is a terrific radio with a great receiver, but the KX3 will give it a run for the money.

In the ARRL DX contest on Saturday night, I worked a few eighty meter stations, including one Caribbean station. Of course, my efforts were with using only five watts, the official QRP CW power limitation. It was almost effortless.

On Sunday, I spent a couple of hours on the HF bands chasing DX stations, and recorded about twenty contacts. Some of these were stateside stations, but I worked several Caribbean islands, including Puerto Rico, Aruba, Monserrat, and others.

South America was coming in, and Brazilian stations were worked without much trouble. Central American stations in Costa Rica and Belize were also logged. I heard no Mexican stations, and only one station in Chile. I was unable to work any of the two or three Venezuelan stations.

European stations were not plentiful, and my only European station was in Ireland. I worked bands from 10 to 40 meters Sunday. The best band was 20 meters, with 40 meters being very active. It was not a great weekend for DX, but the stations I worked were with only 5 watts. I was impressed.

The reason I acquired the KX3 was to have a radio that I could take on trips, and work out of a hotel, bed and breakfast, or one of my extended family’s houses. I want the ability to play radio while my wife and her buddies do what ladies do. I want to have my own agenda.

It looks like I will do more operating with the KX3 from my QTH. QRP is great fun, especially with a great radio.


It’s Field Day!

picture of tri-band antenna for NFARL field day
Tri-Bander Preparation

Our local club, the North Fulton Amateur Radio League has been preparing for months for this Field Day. Last year, we scored #1 in the nation in Category 3A and have tasted victory. We want more. It is an intoxicating thing, winning.

We have gone to great lengths to train new hams to participate in the operating side of Field Day. Like most large clubs, we have band captains and station bosses to make sure that all operating positions are on the air all the time. This is always a problem in that some people want to operate for an hour, and then settle back and enjoy the barbecue.

You cannot have a Field Day without barbecue, but the real reason for the ARRL to sponsor the event is for local clubs to practice their emergency capabilities and show that ability to the public. Our barbecue was catered by one of our fantastic local ‘cue emporiums, and  hamburgers and hotdogs were grilled on site.There were lots of side dishes and deserts to make the most devoted sweet tooth happy.

It did not rain this weekend. Propagation was fine for a summer weekend radio contest. The contacts started out fast and continued at a good pace for most of the evening. In my CW operating position from 10:00 PM to 6:00 AM, there was the inevitable slowing down as the ionosphere lost it’s mojo on the dark side of the earth, but it picked up smartly at dawn.

The logging program we used this year was the N1MM log for Field Day. Besides being free, it was a powerful program and facilitated running contacts. It was great. However, not being familiar with N1MM, I had some minor problems not the least of which was how to edit a falsely typed call sign without re-transmitting the entered information. Oh, well. That’s part of growing up.

By the way, I did work N1MM during the wee hours of the morning.

Now that I have had some rest, it is time to count the Q’s, and start making plans for next year’s Field Day.

Seventy-Three, everybody!

AZ-EL Satellite Antenna on NFARL trailer
AZ-EL Satellite Antenna on NFARL trailer

Resurrection Blog


NFARL logoIt’s time to resurrect my ham radio blog. My last k4bb.com blog was hosted by Blue Host a hosting company that came well recommended before they were acquired by Endurance International Group, a gargantuan holding company. I believe that customer service quality has decreased since I initially bought three years of hosting services.

The problem was that viruses appeared in a couple of my web sites, and all my web site access was suspended until I could clean things up. I tried, even to the point of deleting entire web sites, but to no effect. They told me that they would clean the sites for $250. I declined to pay to clean their server. I had no control over their end of the system, and they wanted me to fix their problem at my expense.

k4bb.com is here resurrected using WordPress.com hosting and software. I have used the WordPress software platform for years on various sites and blogs. I have another blog on WordPress.com, and don’t remember any problems over the last several years. Their hosting is world-class because they control the software, access, and have appropriate security measures online all the time.

I will be writing about regular ham radio stuff. More immediately, Field Day is upon us and I am looking forward to manning the CW station at the North Fulton Amateur Radio League event from midnight Saturday to four o’clock Sunday morning. After that, I will take a turn at the SSB station.

73, and come around often.