KA9EAK QRO – Update

Back in October I purchased a Heathkit SB-200 amplifier. The pictures in the original post show that it was a bit dusty from sitting for quite some time but otherwise it was in good shape and best of all it was not modified through the years. I purchased the Harbach updates but they largely have sat waiting for time to build, install, and test them. With time off for the holidays I was finally able to complete the work and I got the amplifier on the air yesterday afternoon. All appears to be well. Voltages and currents are where they should be in addition to no smoke or loud noises.

SB-200 HV

SB-200 HV

With 55 W of drive from my TS-590SG I am seeing a peak of 500 W on 40m SSB which is just where I wanted to be. I’m not interested in pushing the amp to its limit. The first contact with the amplifier was Frank, WA3RSL on 40m SSB late in the afternoon. I started the contact with the amp off and finished with it on with a nice and noticeable signal improvement as reported by WA3RSL. Frank has the same radio and also an amplifier so it was nice to walk through bringing it up with someone with the same radio and experience with using an amplifier with it. Second contact was Scott, K3IVN with a good signal report as well on 40m SSB. Later in the evening I was able to contact ZS6CCY on 40m SSB with a 59 report after only a few calls in a messy pile-up with a fair amount of noise and QSB followed by YV5AL, HI7MC, and J6/NY3B all with relative ease and great signal reports. I was happy with the investment.

I had purchased the power supply board, soft start, keying interface, and cooling fan updates from Harbach Electronics. Once they were all built and installed I brought the amp up on my Variac and there were no surprises and the high voltage looked good at 2250 V. The last step was to build the interface cable for the TS-590SG. Thankfully Kenwood provides the DIN connector with the radio and JG1VGX provided a very nice explanation of all of the possible ways to connect the TS-590 and TS-990 radios to amplifiers.

Here are some before and after pictures of the amplifier:

SB-200 top view

SB-200 top view

SB-200 Bottom view

SB-200 bottom view

In addition to the JG1VGX site referenced above I also found the following three sites helpful for this project:




While there is some more testing to be done across a few more bands I’m very happy with the results thus far for the amount of money invested. In 1964 an SB-200 went for $200 which inflating the dollars to today is about what I have in this amplifier. I essentially purchased approximately one S-unit which is all that I set out to do and I learned a lot along the way which is much more valuable than the S-unit.

1964 SB-200 ad

1964 SB-200 ad


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s