Keep your nose to the finals

I work with NC State University faculty, staff, and students who do “community engagement” or research and education in partnership with community members off campus. Last week I arranged a tour for a committee I’m on of, among other places, the Historic Yates Mill County Park in southwestern Wake County. NC State owns the mill building and Wake County runs the park.

There were no nails used in the original mill structure, just mortise and tenon joints and pegs. Two mortises are visible on the right where a dividing wall once was. Tool marks like the ones visible on the wall plate (?) are used to date and analyze pre-industrial woodwork.

Our host, Park Manager and historic preservationist Matt Fryar, told us that the idiom “nose to the grindstone” came from millers who needed to check the temperature of the millstones and flour to make sure the works didn’t get combustably warm. They kept their nostrils near the granite to detect the smell of smoking flour.

The same week I got a gristmill tour from Matt, I put a new, preassembled QRP Labs QMX+ 160–6m multi-mode transceiver on the air. The kinds of heat issues millers deal with were on my mind since I had already blown up a different QRP Labs product, a high-band QRP Labs QDX digimode transceiver.

I foolishly connected a 13.8V power supply to it, releasing the smoke from a couple of the BS170 TO-92 MOSFET output power transistors (a.k.a. “finals”) and a 74ACT08 surface mounted device (SMD) chip. The QDX sits on my metaphorical “bench” now, awaiting repair and future activation as a dedicated ultralight portable rig.

Not wanting to repeat my previous error, I’m taking lots of measurements and precautions with the QMX+ power supply. As it says in the manual, when designer Hans Summers(G0UPL) specifies 12 volts, he means 12 volts! A precaution includes putting my nose to the transistors…or at least my finger!

I’d like to be able to run the transceiver as a WSPR beacon sometimes, but the WSPR protocol has a transmission with a 111 second duration. Or, as Summers says in the manual:

WSPR transmissions operate a continuous 100% key-down duty-cycle for almost 2 minutes. You should check carefully whether the BS170’s get too hot during this period. WSPR is much more demanding on the PA transistors.

So I took the top off the QMX+ and ran WSPR for several hours at a transmit rate of 30%, twice or more my normal transmission percentage. I touched the heat sink (a washer) on top of the BS170s to see how hard they were working. That is, I put my nose (thumb) to the grindstone (finals) of the transceiver.

The top of the transceiver is off and I’m touching a heat sink. Lots of copper-wound torroids and IC chips are visble inside the radio. — A QRP Labs QMX+ with its lid off and my thumbs on the heat sink for the BS170 transistors.

There was very little warmth on the washer heatsink at the end of the transmissions and after two hours of transmitting every six to eight minutes. I’m now feeling more confident about running the QMX+ as a standalone beacon while I’m away at work.

As a new ham, I think about whether to invest in trinkets like an infrared laser thermometer to do this kind of measurement more precisely. Though there may be a time and place for more precise thermal management, perhaps putting my nose to the grindstone is adequate for now.