Making: it’s what people do on weekends.
In our first episode, we will tackle a medium-complexity problem in electronics.
While many people are put-off by such endeavors, with an almost superstitious belief that there “is magic in all those wires and parts” nothing could be further from the true. In fact, electrons always follow the rules of simple physics – much to the consternation of poor humans, ill-equipped at times as we are to understand and follow such rules… So to this weekend’s adventure!
The Electronic Detective
The Case of the eBay Amplifier
Allow me to introduce myself; I am the Electronic Detective but my parents named me Phaselock Home. I operate my detective consultancy from L-21(b) Inductor Street, not far from High Pass in the Filter district.
The case began with an amateur operator trying to recreate his ham radio childhood. His “Elmer” had owned a Drake 2-B receiver with the 2-BQ Q-multiplier. The transmit side consisted of a Gonset GSB-100 and a Johnson-Viking Courier linear amplifier. A TA-33 (Junior) beam sat squatly on top of his single-story house, raised by only a 6-foot tripod. A repurposed AR-22 TV antenna rotator moved antenna headings. It was 1964.
Amazingly, in side-by-side testing, my client’s Drake 2-B was as sensitive as his recent (2015) Kenwood TS-590S transceiver. Not as stable for digital modes, though.
The GSB-100 worked well, also, save some sideband suppression issues that promise another case, should my client be unable to follow the straight-forward directions for alignment common to to phasing-type SSB equipment.
The amplifier? Well, that was a different matter.
My client, you see, is a vintage radio addict. He learned to always enter a “Make Offer” bid 40 percent lower than the “Buy It Now” (BiN) prices on eBay.
In this case at hand, a $400 offer, plus a small fortune for shipping, was accepted for a complete, working Johnson Thunderbolt amplifier. Buying with the “make offer” option ensured that if later resold, the odds of a profit would be higher.
Upon its arrival, additional help was hired to help move the beast. Watt’s son was fortunately at hand allowing 125-pounds of “desktop” equipment to be moved into position. My client had inspected the unit, and installed necessary tubes.
But, he was confused by large number of voltage regulator tubes. The marking of tube numbers were unreadable on most.
Here, my years of experience paid-off. Taking a tube, I rolled and rubbed it through my hair as my astonished client picked up his jaw. “Those things are dirty!” he exclaimed.
While indeed they were, the fine oil from the human hair adheres to the places where the numbers used to be. As the numbers appeared, we were suddenly able to sort out an ancient OC3 from a a nearly identical looking OD2, and so forth.
Next came an appearance issue:
The Thunderbolt had a crank to move the rotary inductor as it left the factory. So I demonstrated how a piece of wooden dowel, and a 1-inch long 8-32 screw could be made in one’s drill press.
Esthetically, it was not a permanent repair. A painted screw head, preferably Phillips, would be located later, along with some hollow black plastic tubing of suitable diameter. But, when prosecuting crimes against the spectrum, expediency is paramount.
A further problem was the antenna change-over relay – smashed in shipping. Its robust mechanical parts were intact, but the leaves of the relay, where contact is made, had been bent into useless condition.
With 20-minutes labor, the relay was disassembled and parts bent-around, just so, to make them work as desired.
Those “buttons” at the end of the relay were the issue. They are shown here after my client learned the art of “relay detecting.”
The Thunderbolt, I instructed, was an odd duck having no internal provision for transmitter-receiver switching. The most solid arrangement, although a bit 20th Century, involved the use of two antenna relays drive by switched transmitter AC provided by the GSB-100.
If you inspect the picture, you will see that un-powered, the top two buttons are connected. We call this a “normally-closed” (often abbreviated NC) position. When energized, the relay center pole (the next leaf down) disconnects from the NC and contacts the third leaf down.
When not transmitting, as in the photo, there is no path from the second leaf to the third making this contact “normally open” – abbreviated “NO.”
These three wires are mechanically pressed into a jack (lower middle) here, in the lower left of the photo.
I’ve given my client instructions to continue his quest for a proper plug to make with this socket. But, since this is a 1964-era amplifier, the number of necessary components to create a “factory-fresh” restoration are very limited.
My client is still looking for Johnson Part # 22.1190 to mate with socket Part # 22.1191.
Our time is limited, but the Electronic Detective does offer elucidation to his clients.
Related to this case, observe as follows:
1. The amplifier in question offers a superior product compared with typical grounded-grid designs. “Modern” amplifiers, you see, were designed to be drive by the prototypical 100-Watt (output), usually Japanese-made, single sideband transceiver. “Old” ham gear can be virtually any power level. In fact, you can drive a Thunderbolt to a full 2KW PEP (input) with a low power radio such as an Elecraft K3 or even the new uBITX, a $119 (including shipping!) all band transceiver out of India! (http://www.hfsignals.com/index.php/ubitx/ )
2. This flexibility comes because the Thunderbolt does not drive the cathode (which is how grounded grid amps are driven). Instead, they are grid-driven. Admittedly, there is more complexity. Those three wires on the Thunderbolt switch operating and cut-off bias on the two 4-400C amplifier tubes which are nearly the same (though shorter) than the 3-500Z tubes.
3. While grounded-grid amps are most commonly cut-off when not driven, a grid-driven amplifier is not. Which is why bias-switching becomes important.
4. Sources for restoration parts include eBay for most things, including tubes and such. The Boat Anchor Manual Archive (BAMA) [http://bama.edebris.com/manuals/] is the premier source for FREE copies of manuals. Surplus Sales (of Nebraska) has many odd connectors – they’re moving so we haven’t found a Johnson 22.1190 from them yet. K5SVC (who runs an eBay store) has good prices on tube sets, while Hayseed Hamfest offers an assortment of newly-built (to spec.) can-type capacitors and complete radio re-cap kits.
The Electronic Detective doesn’t recommend a serious boat anchor project of this sort for your “first-time, out-of-the-box” encounter with ham radio’s glowing tube-enabled past. Not only are there LETHAL VOLTAGES involved (which can hurt ‘all the way dead’), but you’ll need to remember that mercury-vapor rectifiers (such as the old 866-A’s) need to be “cooked” for several hours before first user after shipping so as not to arc-back internally. That can be expensive.
In a further adventure, perhaps with the help of Watt’s son, we will tackle something simpler: A quick restoration of a triple-conversion receiver.
For now, I’m back to chasing Moriarty, again.
No, not the villain. You see, I have as my goal this year to work half of the 80 hams who live in Moriarty, New Mexico! I missed all of them in yesterday’s running of Winter Field Day.
To the bench, Watt’s son! And bring a meter. The solder’s a-smoke!
With that, the Electronic Detective put on an oddly shaped piece of head-gear: A Danish Army helmet replica from WW II. No point holding to convention, around here…