Bob Thomas, VE3TOU

Godfrey, Ontario, Canada

Founder, Treetop Circuits · SSB Adapter Designer · Licensed Amateur Since 1958

Bob Thomas, VE3TOU, is the designer and founder of Treetop Circuits — the small Ontario cottage operation that for thirteen years produced what were widely regarded as the finest commercially available SSB adapters for vintage military and commercial HF receivers. Operating from Godfrey, Ontario, with his wife Catherine handling production and shipping, Bob built Treetop Circuits into the definitive source for anyone who wanted the R-390A, Collins 51J, Hammarlund SP-600, or Collins 75A-series receiver to finally perform on SSB and CW the way its exceptional RF and IF engineering had always warranted.

Bob is a retired electrical engineer who has held an amateur radio licence since 1958 — a span of more than six decades that places him firmly among the generation that knew these receivers as current production equipment, not collector pieces. That background informs everything about the Treetop Circuits product line: the engineering is clean, the documentation meticulous, and every design decision reflects someone who understands both what these receivers are capable of and what the people operating them actually need.

The Product Line

Over its operating life, Treetop Circuits produced five SSB adapter models, each tailored to a specific receiver or family. All use a single-balanced product detector architecture with wide dynamic range, paired with a dual-time-constant AGC system designed to resist blocking on impulse noise while providing the fast attack and smooth recovery that makes SSB copy comfortable over long operating sessions.

SB-390 — For the R-390 and R-390A. Mounts externally on the back terminals; powered from the receiver; AM operation completely unaffected. Introduced 2013, refined through five documented revisions.

SB-51 — For the Collins 51J-3, 51J-4, R-388, and R-388A. Successor to the original PD-3, with improved AGC hang characteristics and dual-time-constant impulse noise resistance.

SB-600 — For the Hammarlund SP-600 Super Pro series. Developed in collaboration with community members; mounts under the chassis.

SB-75 — For the Collins 75A-2 and 75A-3 receivers. The same core circuit architecture as the SB-51, adapted for the S-Line era Collins.

The SB-390 for the R-390/R-390A was the product that most defined Treetop’s reputation in the boatanchor community. It went through five documented revisions over its production run — a sign of a designer who continued refining his work rather than treating a first release as final.

Thirteen Years and Seven Hundred Units

Treetop Circuits operated from 2009 until the early 2020s, shipping over 700 units in total. For a two-person cottage industry serving a niche collector market, that is a remarkable output — and each unit represents a vintage receiver now performing closer to the standard its original engineering always merited. Bob described Treetop as a “retirement project,” which understates what it delivered to the community but captures the spirit in which it was run: not for profit, but because the problem deserved a proper solution.

When Bob announced the wind-down, Perry Sandeen KM6FQV acquired the business assets with the intent of continuing production. The practical challenges of succession in a specialist operation proved formidable, but the effort to preserve what Bob had built speaks to how highly the community regarded it.

Public Domain by Choice

In a final act that is characteristic of the community’s best contributors, Bob released the complete manufacturing information for all Treetop adapters as public domain — schematics, PCB layouts in ExpressPCB format, alignment procedures, and test rig instructions — all freely available for anyone to build, modify, or sell. His note accompanying the release captured his attitude precisely:

“It’ll be interesting (though perhaps humbling) to see what improvements someone makes to my designs and methods.”

— Bob Thomas VE3TOU, Treetop Circuits Build Your Own page

That willingness to hand over sixty-plus years of engineering judgment to whoever wants it — with no conditions attached — is the mark of someone who cared more about the receivers being properly heard than about protecting a commercial interest that was, by that point, already fulfilled.

Mike Peace VK6ADA / r-390a.net Administrator
Boatanchor Legends Tribute Series — Preserving the History of the R-390A Community