In the Saturday report we got into the basics of restoring an old transmitter. Like restoring an old car, what could be so hard, right?
Well…Let’s sit back and take a look at the radio chassis after taking off the front panel:
This is after taking the sheet metal off from around the “tuning knob” (VFO = variable frequency oscillator) in the middle of the chassis. A series of long stand-off spacers holds it above the main chassis.
We immediately spotted two problems with the VFO – that which tunes the transmitter to the right frequencies: These will jump out at an old-timer:
See the problems? The first is that there are new and old components that have been cobbled up by someone who didn’t know what they were doing in the past.
The tip-off is that the new resistor, center left (violet, gray, orange) that looks too “fresh” for a 60-year old radio. We can also look at what the colors mean. Over at All About Circuits there’s a good intro to resistor color codes.
Lemme see: Blue is 6, gray is 8, and orange means “Hang three zeroes on the numbers of the first two bands…” In other works, 68,000.
We will off to look at the circuit (schematic) in a second, but I didn’t recall any kluge totally about 91,000 ohms (the new resistor is in series with old components for 91,000 or 91K ohms). Unless we can find where there’s something in that range hanging on pin #1 of the tube socket, where we note an OA2 voltage regulator tube lives, we have bought a radio “stiff.” Which is a great feeling when you can wave a soldering iron and raise a radio from the dead.
In other words, this radio doesn’t appear to have been in “running condition” when it shipped (even before the accident).
We go looking around tube V-15. We know – since the kluge is how high voltage should have gotten to the VFO tube (V14) and it would be too low to work right – if at all – we have made tremendous progress.
See the highlighted part of the diagram?
You will see there should be one resistor (R73) which should be 18,000 ohms (18K). Obviously, someone got to the right general area where a part had previously been replaced, but when they got there, they put in a stack of resistors offering four times the voltage drop required. That would have been low enough to keep the unit for working.
I didn’t have an 18 K 2 watt resistor on hand, so I ordered a kit of 5-watt resistors from Amazon. Sooner or later, they’ll show up and we can continue with the project.
We also make notes like this because there is always an outside chance that the value of the kluge might have been right if some previous Golden Screwdriver Award Winner had opted to hook up the VFO power from the +600V supply instead of the +300…but there was no evidence of that level of engineering. Still….you never know until it’s all back together again.
By the way, rearranging power that way would be dumb since the high voltage supply (+600) jumps around a lot more (especially on voice peaks when transmitting) than the low-voltage supply. But again, you never know what goes through people’s heads. Solder smoke makes some people really dangerously dumb…
Tinkering like this is addictive. Reminds me of rebuilding a car engine where there’s that moment approach ecstasy when the engine catches, fires and runs after reassembly! Most people have such a source of pleasure. Elaine’s is word-puzzle books. My friend Gaye does adult coloring books while her hubby’s become an excellent golfer… My son jumps out of airplanes and winter camps high in the Cascades…what can I say?
Still lots to do. For example, in order to repair another smoked part, I had to take apart the mixer sub-chassis on the left in the top picture. And to get that off, I had to take off a dial string and some tensioning springs…
Cascading Failures Followed…
About half the time, you can “make due” when the little hook has broken off the pulley (as it has at the lower attach point) by bending the spring into a hook. About half the time it works, but that wasn’t this time.
Amazon sells spring assortments, too. Yet another hole in the inventory filled, But, another few days with the “big bench” in the shop filled to overflowing.
Now step over to the right of the mixer sub-chassis and have a look at this because there are two items of interest to budding Electronic Detectives. Four, if we count the coffee stains where someone had sloped coffee through the perf-steel top of this innocent old radio. They could have at least cleaned it up…
See that thing in the upper right? That’s a 1/4″ to 1/4″ flexible shaft coupling
As you can see, the plastic used to get the “flex” is very thin. 60-years on, “flex” turns into break super-easy.
And now, if you look at the second picture from the beginning of the article (where I mentioned two things to notice) you can see what is wrong with the VFO: A Flexible Shaft Coupler on the VFO frequency tuning shaft is broken. And that sent us to scrounging around to see what we had that might be used
With nothing on hand, it was a quick trip to eBay where two such couplers were found (new old stock, too!) at a reasonable price.
Also of note in the above picture, you’ll see that bread-slicer looking thing (a variable capacitor) and next to it is a vacuum tube inside that metal tube shield. That capacitor has a couple of hundred volts of DC on it. And, if you try to move that tube cap so it doesn’t make contact with the “hot component” you can, as I did when much younger, fly through the air (withe thre greatest of ease!) across the room. I’m alive because of the “keep one hand in the pocket rule.” And I wear tennis shoes that are clean and dry and nitrile gloves,, too….That’s how I plan to top 70 next month.
That left only one more mystery to be solved pending installing new old stock tubers for the ones ruined in rough shipping and seeing if the repairs were sufficient. See if you can spot the “mystery” in this picture:
Sharp? See the red wire just dangling in space there? It needs to attach to something but I need to trace out what. There’s a low0violtage power supply filter capacitor above it, and the high-voltage filter below. Or, maybe it went to a ground, but not with a red wire. Unless the same Golden Screwdriver lad…let’s not go there…
Wire and pray the guess was good? I’ve found 5-minutes of matching components to schematics and toning things out is a lot less expensive.
If you look down and under that shaft (just down a bit from under the red wire), by the way, you can see the tiny aluminum angle brackets that were recreated to mount a small board that holds bleeder resistors and new capacitors for the power supply. 24-karat snots to get mounted. (“Elaine, can you come over here for a minute…I need your eyes and hands smaller than mine…”) She’s a great sport about things like this.
An ideal ham radio family include one partner who is large enough to even lift a radio of this vintage. A small-sized partner – with tiny hands – is deal for sub-assemblies which is where KG4YHV (Elaine) gets involved in hamming.
As parts come in, I’ll eventually get things all put back together and I’ll get it on the air. Depending on the next smoke test, of course.
I know there’s no rational reason to keep three HF stations on the air (with three amplifiers, too) but ham radio is, as someone told me years ago,”…more like a disease than a hobby…”
Hams will play along with that…just like people chide the classic car collectors, too. “What? Can’t afford a newer car?”
Pay such people no mind. They belong to the disposable society and that, dear reader, is why America’s in such a heap of crap right now. We used to mass produce products like the Pacemaker. Today, with the exceptions of MAGA firms like TenTec and Elecraft, most ham gear comes from Asia.
Two other companies that deserve special mention: THE radio kit company that dwarfed all others in ham radio kits (back in the day) was Heathkit (of Benton Harbor, Michigan). They went bankrupt – they’d made an error getting into education kits too early – before the STEM rage caught on. The good news is they are working on recovery and we hope to find another product to buy from them (and build) one of these months.
The other is DZKits up in Loveland, Colorado. Their top-end kit is a transceiver called the Sienna XL and, depending on how budgets and time allows, I have looked seriously at building one – all decked-out, of course.
My personal reasons for building a Sienna XL are pretty simple (should time and money come along!): First, it’s a build it yourself piece of equipment offering high-end performance. While it’s true that Elecraft also does “kits” to get to performance levels of their K3 series, there’s a lot of small stuff – and that comes prebuilt.
The Sienna on the other hand, lacks the DSP capability, but that’s because it’s an analog radio (except for frequency generation and such). What that means is – and this depends on your “ears” – the analog radios tend to sound better.
My brother in law, Panama Bates, was over earlier this week and seeing me work on the Pacemaker, he asked about my fascination with tube-type gear. “We’ll, come on in and take a listen…”
I set up two radios – my Kenwood TS-590S as the digital representative – and my lovingly restored (and still being upgraded) Hallicrafters SX-117 for a side-by-side on the same antenna.
After a few minutes of listening? “You know, I can hear what the people on the tube radio are saying – it’s very easy to understand…” Panama judged.
And he was right. Could I have spent 10-minutes, brought up the Beverage receive antenna, a dedicated pre-amp on the Beverage and gotten the Kenwood to “win?” Sure. But this was an apples-to-apples.
That’s why in the recording industry even today, Neumann mics and some with tubes in them, are still considered “state-of-the-art.”
My thinking is that people need to be a lot more circumspect with regard to consumption in our “disposable society.” It’s also why I’m doing a short book length core dump on emergency power systems on the Peoplenomics side of things.
Any damn fool can write checks. The art and science is learning how not to need to.
As we say at The Antiquities Bureau, another project: “The Future is Right Behind Us.”
Write when you get rich and I’ll report down the road on the smoke test when it’s all back together.