This is a Boomer 600 broadband HF amp. This type of amp is readily available at swap meets and on the market, and most work really well with QRP rigs, low power SDR rigs, etc. When used with external bandpass filters, they are a great addition to a low power operation.
A friend picked this up at a swap meet, DOA. I found a burned and damaged contact in the T/R relay. Once working, I discovered a SWR issue on the input, due to an input transformer mismatch (possibly as a result of different power transistors than the original design, not sure). I corrected the transformer ratio, altered the input pad, and all was well.
Next, the 2nd harmonic on the output was only down about 20db. Despite it being used with an external bandpass filter (60dbm.com), I felt this needed to be improved. Using arco trimmers temporarily sub'd into the output tuning stages in place of the fixed values of C as supplied, and the Spectrum analyzer, I was able to achieve around -30 dB. I dialed it in, measured the Arco's, and installed fixed value caps in their place. This helped improve the performance of the downstream bandpass filter. Here's a few pics.
