Making: The Electronic Detective, Case #1

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!

(Continues below)


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! ( )

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) []  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…

11 thoughts on “Making: The Electronic Detective, Case #1”

  1. Regarding your discussion of yesterday – and today’s blog – I propose that there will be a good job market for people who can ‘fix things’ – especially things that are ‘too expensive’ or not readily movable to take to someone someplace to fix.

    When I was in high school, I came home one day to find my mother bemoaning a problem with our dishwasher – it wouldn’t drain – and we didn’t have the money to hire a repairman.

    Since it wasn’t having to do with the motor (not touching that!) – I suggested that we take it apart, focusing on the water drain. Lay the removed parts on the counter and after finding the problem, replace them in reverse order. I figured even if I never had done this before, I could do it.

    Mom was skeptical; In her eyes, I was in ‘mess with her stuff dog-house’ ever since I broke her sewing machine at age five. Long memory on that. So she watched me like a hawk while I spread the parts out on the counter.

    Everything proceeded apace until I got to the drain itself – put my fingers down in the hole and found some pennies – three or four if I remember – and pulled them out, laying them on the counter.

    “What are those doing there?”, exclaimed Mom – and she stared at me like I had something to do with that. I didn’t know but I had my suspicions – the youngest member of our family, who was six years old liked shiny pennies – probably thought they needed ‘washing’.

    Then I put the dishwasher back together – again under the eagle-eye of Mom, and it worked perfectly.

    I think that if someone is of a curious mind, there will always be a job available for such a person.

  2. Dear Det. Phaselock,

    A question if I may….

    I have 2 BA projects awaiting my attention. One, a Hammarlund HQ110C that is in a box with he case removed and all the tubes in a separate box covered with years of dust. The other an old Heathkit receiver I have not determined the model as yet.

    My question for the learned Detective. How does one employ your method of “hair-raising” old faded tube markings if they have suffered the rages of years and lost all of their hair?

    I have already made a request to my loving spouse for assistance but she quite loudly and with extreme prejudice refused to cooperate and suggested I try elsewhere.

    Not quite certain where “elsewhere” she could mean is but I doubt I want to know anyway.

    73 AD0YQ

    • Haven’t tried public of pit hair, but there are always options for the creative!
      An alternative is a forgiving tube checker. Yet another way: get the schematic of said radio – got to tubedepot or other online places that have tube manuals. Measure tube. Compare with book.

      Realize that the short-squatties with 9 pins and two plate structures will possibly 6u8 or 12 au7/ 12 ax7, etcs. 7 pins tall could be a 6AQ5 or if in the power supply, maybe a 6X4…and so forth.

      Key lesson: Get the manuals! This is how I got on to the problem in the thunderboomer – bad VRT tube – but how would that kill the amp output?

      Simple: The VR tube failed from over-voltage when the 4 K load resistor failed. That had Kept a lower bias voltage on the final tubes. THAT in turn kept them from making power. And with the resistance chart in the manual…piece of cake to find it. Being half-blind and hands the size of bricks makes repairs like the finals of the longshoreman’s swearing contest…but hey…this is what “making” is about!

      Meantime, got the TBolt on the bench and the issue seems to be the crappy bias set up. Absent the faulty 4 k load resistor, bias went high, keeping the tube mostly cut off, ergo about 300 w out. A change out of parts and some new components in the HV section and we MAY get this back on the air today…time will tell…

  3. George – Could you dumb this down a bit. I recently purchased an “Elenco Practical Soldering Project Kit – Build a fun two tone European siren”. It is designed to teach you soldering & give you a project to practice on (My Christmas Tree HO Train repair soldering experience was a bit messy). My goal is to build a Lionel Train Village – O Gauge on a small sized ping pong table we don’t use any more. I chose O Gauge because the larger size will make it easier to work with. I need to measure everything to make sure my idea will fit.


    what.. 768 million in aid to terrorist breeding grounds.. wny not to some of our abaondoned industrial towns that look like a war zone..

    then they wonder why our president takes the stand he does and condemns him for it..

  5. Interesting. I stopped playing with tubes when I was about 12 and went on to transistor control logic, FWIW. I’ve always been a bit more of a digital sort.

    The exception was PMT’s in scintillation counters, where I got my fair share of high voltages. Now, decades later, schematics are easier to read than Chinese, though I’ve been studying the latter with vigor. It’s interesting that you mentioned Moriarty. It’s an easy drive from here and I had no idea that they had 80 hams! Perhaps I might still become one. BTW, they also have a nice GA airport. Unfortunately, they’re right by the freeway.

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