- 2024
- Oct
- 30
A Waterman OCA-11A “industrial / pocket” oscilloscope.
This little scope came from the recent MARC hamfest, and was sold as not working - the previous owner stated that someone had removed tubes, and all he did was verify the heater in the CRT was lighting up. He was right, someone removed all of the 12AX7 tubes as well as a 6U10 compactron, leaving only a 6AG11 compactron in place. All of these devices are triode amplifiers, with the 6AG11 having two diodes in addition to the triodes.
The device appears to have a solid-state power supply with solitary diode. There’s some small evidence of repairs being made over the years, but for the most part it seems to be fairly original.
Tube compliment for this device is:
4x 12AX7 dual triode
1X 6U10 triple triode
1X 6AG11 dual diode/dual triode
The device is capable of operating on 50-400Hz @ 115VAC
The front offers all the controls, and uses pin jacks for input on a strip at the bottom. That’s kind of unusual. The metal under the paint appears to be oxidized, and the enamel with the lettering is flaking off. The potentiometers are brought out to the front by long internal shafts, some of which are bent. This could be an easy fix, as they’re just connected internally with nylon unions.
The back offers a cord wrap and some screw terminals, presumably for grounds. It also offers a badly exiting cord from the previous owner.
The device is relatively clean inside with the transformer, power supply, and high voltage all riding in the back.
The bottom is well packed, but there’s no wax paper stuff as far as I can see. Looks like films and other decent capacitors, but I bet some of those carbon comp resistors are drifting. There’s an electrolytic that’s probably baked out, and some neon bulbs of unknown type probably being used as regulators that would need to be replaced, but that’s about it.
You can see where the previous owner removed all of the “good” tubes. The 6AG11 is also a triode pair, so I’m not sure why they didn’t remove it as well. Fortunately, if you’re not concerned about the make of the tubes, all of them can be relatively cheap - there’s about $25 worth needed for this device.
It’s an interesting little scope, and would be perfect for a benchtop radio repair station - tube scope with tube inputs doesn’t care if you hit B+ for a second.
I think I may give it a shot and see if it will live again. If someone out there has a schematic for this unit, I’d appreciate a copy.
- 2024
- Oct
- 29
A Heathkit IG-72 Signal Generator Part 5 - We’re not done yet.
I was warming the device up for final cal. I had just completed it, and put it back in the case. Back on and SNAP.
I did some measurements. Nothing much of note. Removed the tubes, applied power. ZZZZZZZ right on the socket for the 6X4 cathode. WTF???
I removed the wire from the cathode to the filter capacitor. Nothing. I reconnected it to the choke. A nice spark was jumping from one of the plates to the cathode. Removed the wire on the cathode and did a measurement from cathode to plate pins.
There’s nothing connected to this pin other than my meter. 60Ω is not a good measurement. It came and went as the pin was moved around.
It looks like this double-wafer socket may have some carbon tracking inside of it. Oh fun! That means trying to figure out something to replace it. I have some sockets in stock, we’ll see if there’s one that can be used here.
Of course I don’t have the correct socket - these are 1” mounting centers, which is an oddball size. Most are 7/8”. Off to eBay for the rescue!
Stay tuned!
Next part of this series: https://wereboar.com … back-up-and-running/
Previous part of this series: https://wereboar.com … no-need-for-repairs/
- 2024
- Oct
- 28
A Heathkit IG-72 Signal Generator Part 4 - Final - No need for repairs.
This is probably one of the easiest devices I’ve had to fix - there was really nothing wrong with it beyond needing a new power cord and a tuneup.
A tuneup, in this case, consisted of some Deoxit in the controls, and a new power cord:
There are three reasons I’m replacing the power cord. First is the fact that the old one is about that close to being hard plastic. Since I have it open, it may as well get a new one. Second, I can replace it with a polarized device. This isn’t a hot-chassis set, but I’d rather have the hot on a switch. Third, this just doesn’t look good to me:
I’m also going to replace the tubes. The old ones aren’t bad, but I bought new ones, just in case. There’s no need to not use them, and the old ones will go in the boxes as spares. I’ll probably pick up another new set, but I can’t imagine these will go bad in my lifetime.
You can also see the new power cord exiting the back of the chassis.
There were two of the original Mullard tubes, and one RCA. The getter flash on the RCA tube looks a little baked compared to the new one, which is a nice, shiny RCA device.
In order to calibrate this, I basically ignored the manual. Since we have DVMs with more than 500 ohms/volt impedance, we can calibrate the device directly. Take note, however, that the device needs to be good and hot before doing this. Let it warm up for a long time to stabilize. I’d suggest taking it out of the case and putting a cardboard box over it. Also note this device was designed to run on 110VAC, so you may need to variac it down a bit.
But, to start, I did a quick beginning cal on it. I set the frequency to 1Khz, and attenuators to minimum. A scope was connected, as was a digital meter. Frequency was set to 1KHz, course attenuator (switch) and fine attenuator (pot) to minimum. Meter and Oscillator controls were set to about the middle of their range.
You’re going to adjust the osc and meter controls on the chassis. Oscillator is the one closest to the transformer, and mine had a slot in the top. Meter was closest to the edge, and has no slot on mine.
Power was applied and the tubes warmed up. I turned the course attenuator to maximum, and adjusted fine to about 2/5 of max. The unit wasn’t oscillating well, so I turned the oscillator control CCW until I got a sine. I adjusted this until the bottom wasn’t clipped, and then turned it down a bit more.
For the meter, I adjusted the fine control until my digital meter read ~5.0V, and then adjusted the meter control on the chassis until the analog meter agreed. It’s not a terribly linear meter, so don’t be surprised if it’s off some at other points on the reading.
I did notice the signal levels drifted as it warmed up - therefore, let it warm up before adjusting.
I didn’t notice the load switch doing anything. Normally, you would calibrate at load, but I’m not sure why this didn’t do much. I’m not terribly worried about it, the thing makes audio and it’s close enough for what I need to do.
So…that’s it! I’m going to get a box and cover it this weekend while on, let it get nice and hot, and do a calibration - but the device is working with little to no effort.
I have an RF generator to accompany this, I think that may be the next project. Stay tuned!
(Something went wrong during final cal…looks like we do have a problem!)
Next part of this series: https://wereboar.com … 5-were-not-done-yet/
Previous part of this series: https://wereboar.com … t-3-do-i-need-parts/
- 2024
- Oct
- 26
A Hallicrafters S38-C recap.
I picked up this good example of a Hallicrafters S38-C at the 2024 Dayton Hamvention. While it doesn’t look to have had much done to it over the years, it had - of course - bad filters.
In order to remove the old capacitor, a single rivet has to be drilled out. Mine was just below and to the right of the audio output transformer:
In order to work on the chassis better, I removed it from the case. To do this, you’ll need to do the following:
1: Remove the knobs. These are secured by a 1/16th hex screw. See the warning about the feet below.
2: Remove the feet. These are probably brittle and going to break on you.
3: Unsolder the speaker.
The chassis just pulls out at this point. The paint is pretty thin on these units and will scratch easily. I did so :(
Once you’ve drilled out the rivet, it should allow you to pull the old capacitor off the shaft and pop the remainder of the rivet out. I simply cut the leads on the capacitor to get it out of the way but leave a trace in place for the new parts.
This particular capacitor has 4 sections - 40/40/60/20 - all are 150V except for the 20, which is 50V. All of the sections on mine tested ok for capacitance except the 60. This showed practically nothing.
That doesn’t mean the rest of them were any good, they all showed high ESR and loss.
(Oh boy, did I mess that up! Negatives going the wrong direction…It was…yeah, not enough coffee!)
I kind of did a sloppy job here and I’m not really the happiest with the way they lay, but they’re secure. You’ll notice that there is no 20μF - that’s because some stupid little piggy ordered non-polarized parts instead of regular parts. That’s ok…I need to replace the across-the-line bumblebee as well, so another trip to mouser.com is in order.
This particular bumblebee was coated with some nasty oily substance, but I’m not taking any chances. It gets replaced - even if it was good. I also need new feet for the device, some were worn down and one cracked apart. There’s a supplier for those, so I’ll order some and let you know how it goes.
So…into the waiting room it goes.
Stay tuned!
- 2024
- Oct
- 26
A Westinghouse H-636T6 AA5+1 Radio
This is the radio that I picked up at an antique store a few weeks ago. It was pretty obvious that the filters were bad, and the tuning gang was a bit gritty and in need of some cleaning and lube. In order to make this thing play again, the first thing to do was replace the filter capacitors.
Here’s the capacitor’s top. You can see it’s not in the best of shape.
There’s a lot of cracks in the device. The first thing to do is get the thing out of there.
Here’s the spot on the board we’ll be working with. The original capacitor is a 3-leg device where the legs have a crimp that physically anchors it to the board in the square holes shown before being soldered. In this case, there’s enough pad to get solder wick on it. I like to add some fresh solder to get the joint clean and shiny again before wiking it off.
The old solder cleaned up nicely and was removed. Notice there’s multiple holes there, so multiple kinds of parts could be used.
Is the old capacitor actually bad? The doctor says yes:
That’s supposed to be a 50μF, not 8μF…not to mention the 26% loss and 140Ω ESR. Is it bad? Yes. Very yes.
A new capacitor pack was made from two 47μF capacitors. I used some old standoffs rescued from a dead project at a former employer to keep them off the board.
The new leads are much smaller than the old ones, so a lot of solder is needed to fill the pad. Once it cooled, a quick cleanup with some iso alcohol and an orange stick got rid of most of the flux.
Since the plug was clipped into the case (it needs replaced as it’s hard as a rock!) I sliced the old rubber off and pulled it free. I plugged in the radio, tuned it to approximately a station, pulled the knob out and…
WLW, weak but audible greeted me. The first words this thing said in decades was a story about how someone is bombing someone else (again) in the middle East. You could literally be at any point in radio’s history and you’d hear similar.
There’s one last thing this radio needs before the tuning gang gets cleaned and the radio gets an alignment…this part:
Here’s a “Bumblebee” capacitor, or a “bumblebomb” as they’re called. These are a plastic cased capacitor, which tends to crack and leak. This one is directly across the AC line, and it’s going to need replaced. I’m pretty sure I have some suitable replacements here somewhere from another repair. It’s just going to take a minute to find them.
That’s it, that’s really all the device needed to play again - I’m still convinced the seller didn’t know to pull out the knob to turn it on, but that’s not really an issue here. There will probably be a part two later, but there won’t be much to tell on it - just a report on how the alignment went. Stay tuned!
Next part of this series: https://wereboar.com … aa51-radio-it-lives/
Previous part of this series: https://wereboar.com … -westinghouse-radio/
- 2024
- Oct
- 26
A Heathkit IG-72 Signal Generator Part 3 - Do I need parts?
Now that the device is working, the next step is to see what parts are going to need to be replaced in order to make the thing work better.
The short answer is nothing. The capacitors in the filter for the oscillator are on point, the output is close enough that it’s probably not worth changing things, and the filters and electrolytics that connect stages aren’t showing any leakage. That’s pretty amazing for a device this old. I decided to do some checks anyway, just to prove the point.
There’s not much voltage on the resistors in the notch filter. I didn’t check any values, but these are all fairly low so I don’t expect them to have drifted out of tolerance that much.
When the particular part isn’t selected, there’s a little bit of AC on the resistors.
There’s no DC, indicating that capacitors aren’t leaky.
I did some checks on the filters and the other two electrolytics in the circuit - all of them showed a good value with low ESR. At this point, I will probably just check the resistors to make sure they haven’t drifted, and replace those that have. Stay tuned!
Next part of this series: Coming soon!
Previous part of this series: https://wereboar.com … r-part-2-suspicions/
- 2024
- Oct
- 25
A Heathkit IG-72 Signal Generator Part 2 - Suspicions.
I’ve been studying the schematic for this device - it’s not a complex circuit, so there isn’t much that could be wrong with it:
There are two tubes and a lamp used as a PTC that are immediate suspects, as well as the oscillator control. The problem happens on all ranges, so it’s unlikely that any of the filtering circuit is at fault since it’s switched in and out.
The 6CL6 is a cathode follower that provides the input to the 6AU6 so it can oscillate - remember that an oscillator is an amplifier that provides it’s own input. The circuit in the dotted line box is the filter that determines what frequency is being provided. The lamp is used as a positive temperature coefficient resistor that helps balance the signal.
Since the 6CL6 had been replaced in this unit, I started with it. Changing it for a NOS unit made no difference.
The next logical choice was the oscillator control. This regulates the level, not the frequency. The control is outlined in red - the other one is related to meter scaling.
I had the output hooked up to the signal tracer I recently rebuilt, and a noticeable buzz was present. That was the flat spot on the bottom of the signal. With that in mind, I adjusted the oscillator control until the buzz went away, confirming the signal clarity with the scope.
So…the device is working. But that doesn’t mean we’re done. Things like filters and tubes still need to be checked and potentially replaced, and there are some interconnect capacitors that probably should be replaced regardless. I’d also like to tidy up some of those old 5% resistors in the oscillator filter, even though the manual says they probably don’t make much difference. Still…why not. We know carbon comp resistors drift, and modern high-precision parts are cheap. Still, I did a spot check on the capacitors in the oscillator filter:
It’s supposed to be 50nF +/- 1nF. That’s pretty good for a 55 year old part that’s being tested with clipleads. That being said, what’s the leakage and ESR of the part? It will need to be taken out for that to be checked.
Stay tuned!
Next part of this series: https://wereboar.com … t-3-do-i-need-parts/
Previous part of this series: https://wereboar.com … part-1-observations/
- 2024
- Oct
- 23
A Heathkit IG-72 Signal Generator Part 1 - Observations.
I’ve decided to see about tuning up this device I purchased at The Scioto Valley Hamfest, so this will be my next project. It shouldn’t be anywhere near as involved as the last one - but we’ll see.
You’ve probably seen this picture posted here a couple of times:
The device has an output, but it’s flat on one side. The oscillator is working, is fairly close - but is out of balance. This could be tubes, the light bulb PTC resistor, or a bad capacitor. That’s what we’re here to determine.
The device was purchased at a hamfest, as previously indicated. The vendor selling it had a bunch of odds n ends:
I bought this, and another unit the guy had. The second unit had a handle, and was in poor shape overall. It sacrificed it’s handle for the ‘good’ unit.
Since much of what I’ve read points to a tube being not-bad-not-good, I picked up a fresh set of tubes:
The good unit appears to have been a factory build - everything is neat and it has the Heathkit sticker on the chassis.
The bottom uses manhattan routing and has nicely twisted lines where necessary.
It’s hard to see, but the 6CL6 tube in this one is an RCA, while the other two are Heath branded. That one has been replaced at some point - it’s a cathode follower that provides the input for the oscillator, so we’ll look at that first when it’s on the bench.
The other unit, an AG-9A, looks to have been a kit build. It’s clean inside, but not as much care was taken during assembly.
I don’t have any intention of restoring this unit for use, so it will be put back together and stashed with my other parts units. I doubt I’ll bother using the tubes out of this for anything other than display, since NOS units are still available at a reasonable price.
But first, I’m taking the time to do what I normally do with these things - take the half-loose knobs off and give them a bath:
They come out nice and clean. I’m cleaning the other unit’s knobs as well, no use in wasting time in the ultrasonic bath.
Next step is to open the device and check some things against the manual. Stay tuned!
Next part of this series: https://wereboar.com … r-part-2-suspicions/
Previous part of this series: You’re at the beginning.
- 2024
- Oct
- 21
An Eico 145 Signal Tracer - Wrapup and final thoughts.
The signal tracer rebuild has been finished and happily amplifying sound again. What’s next? Here’s some thoughts on this device, and the rebuild process in general.
On the rebuild process:
1. Research the device.
Looking the device over and gathering things like schematics and assembly guides are a necessary first step, but don’t overlook the fact that these devices have been out there for decades. Plenty of people have had them in their possession, and there’s plenty of after the fact info available. Modifications, parts swaps to increase life, general deep dig things that may assist you in putting the thing back together. Read everything you can about the device before starting.
2. Some other tools you may need.
One of the greatest inventions I have on my bench is a tool called an orange stick. It’s not orange in color, but made from (traditionally) orange tree wood. It’s similar to the sticks that nail salons use in that it’s a double-ended stick with wedge-shaped ends - except that it’s longer. These are a soft wood that won’t mar parts, and can be used to push wires and wire-ends around for forming, as well as a soldering block for parts close together. They have a million uses. I highly suggest adding a pack of these to your tool kit.
Also, don’t be afraid to have more than one soldering iron on your bench. I regularly have my trusty 30W Weller, but keep an 80W unit handy when doing chassis work. You may find that having multiple wattages, multiple tips, or even multiple size units on the bench to be of use. You may even find a small butane torch to be useful here. Don’t limit yourself to just one.
3. Parts.
When you’re ordering parts, don’t use the crap you find on Amazon or eBay (unless you can verify it’s of known pedigree.) Get known parts from one of the supply houses. You don’t need to use the absolute top-tier part (unless you want to!) but get a good part. Always get an extra or two as well, in case you break something. It happens! Don’t go crazy buying 100s, but if you need 9, get 10 (and possibly a price break.) Be aware that some parts may have inductance (wire-wound resistors) and you want to avoid that kind of thing unless replacing like-for-like.
4. Be aware of voltages and values!
Capacitors are easily rated by the nomenclature printed on the part. Get at least the rated voltage and value here, but don’t go nuts. You don’t need a 1000V part where a 400V part was specified, but if all you can get is a 500V part, that’s fine. You’re not going to get the exact same values today for most of the stuff (except resistors) so don’t be afraid to go up a little in value. A 22uF part will easily replace a 20uF part in the power supply without issue - just don’t fall into the “more is better” trap because it’s not. Stay close to the rated design specs.
Resistors are a special case. For the most part, the 1/2W resistors used then are easily replaced today. However, be mindful of the voltages - you can be working with 300, 400, 500+ volts here, and parts need to be rated for the working voltage of the circuit. For example, if you have a resistor that’s rated 2W but it’s 2 inches long, then it’s probably a higher voltage device. Using a resistor rated for 500V in a 100V circuit isn’t going to hurt anything.
And, always remember you’re working with line and higher than line voltages here. Don’t be afraid of it, just give it the respect it deserves.
5. Grounds.
Grounds are important. Always make sure your contact points on the chassis are clean, and use washers that dig into the chassis if you can. Soldering those grounds to chassis for a good contact point will also work, but make sure you get a good connection otherwise oxides will build up and give you more grief than you started with. Good fluxing and a clean shiny spot for soldering is important here. Scotchbrite (plastic “steel” wool pads) is your friend here!
6. Signals.
It’s always been good practice to lay your filament and AC wires right on the chassis if possible, and to keep your low-level audio away from those, if possible. Keep it short and covered.
7. Don’t be afraid to modify!
Unless it’s of vital importance that a circuit be laid out the way the manufacturer did it, don’t sweat it if you see a better way. Add a terminal strip to bring parts out from hotspots. Add holes to mount new parts instead of trying to replace the exact old ones. Add a fuse. The manufacturers probably tried to work the assembly to use the least amount of extra parts, but you can take whatever luxuries you need.
8. Be mindful that you’re not the first owner.
There’s probably going to be modifications in the device. There may be added or missing parts. It may be that someone was trying to make the device do something else. Note these modifications before you begin, but don’t necessarily use them as a guide for rebuild unless you can see that it was trying to fix something.
9. Don’t be in a hurry.
The important advice with any kit. Take your time to lay out parts and wires. Check things as you go along, and check it all again when you’re done.
My thoughts on the device itself and rebuilding it…
This is a fairly simple device in terms of operation. A power supply, a preamp, and a power amp. Not much going on here, but there were still some modifications made.
The 6K6 power output tube is run electrically hot in these, about 1W above rated specs according to what I’ve read and calculated. It was suggested that the cathode resistor, R5, be increased from 470ohm to 1kohm. I did so in this rebuild. C10 was missing on my device for some reason, and that was added back in. R5 is the resistor that provides current for the cathode, and C10 is a bypass capacitor to help improve fidelity of the amplified signal. It’s possible that C10 went bad at some point and was removed, as the device will operate just fine without it. I couldn’t see any evidence that it was ever there, however.
I’m not a purist, so I didn’t care how the power supply turned out. The old capacitor was discarded and two new parts were laid in it’s place. I decided to use a 500V non-inductive 25W aluminum resistor here, bolted directly to the top of the chassis, with the capacitors going to a ground also on the top. That probably offended some people, but I need functionality here, not a beauty contest winner. The reason I used the aluminum resistor is because it’s non-inductive, and was available to me.
Terminal strips were reused where possible, with new ones added. These allowed me to space the parts out more, which should help life in the terms of heat related death. It also allowed me to use two back-to-back diodes in the filament circuit to cut down on the voltage, since the device was designed to run on 110 - not the 125VAC we commonly see in the USA these days. Where something was grounded, the tabs for the terminal strips were soldered directly to the chassis to provide a good ground. It’s not the prettiest thing, but who cares.
Last, I had to remove and correct some of the modifications to this device. One of those nasty Amphenol microphone connectors on the front panel was removed (and needs to be filled at some point,) and the audio output transformer was bolted down. The audio transformer in the device didn’t fit the holes provided (device was narrower,) so I don’t know if this was because the original part was bad and was replaced at some point, if the chassis was drilled wrong, or what. A new hole for the transformer and a terminal strip to provide ground for the power supply mounted in the old hole fixed both those.
The only other thing is deciding how to fill the front panel hole. I could use a BNC connector, but since this probably will never see IF frequencies, do I care? Originally, I though about just plugging it with a plastic plug I had laying around, but I’ve kind of warmed up to using that hole as a ground tie point, or maybe just a tie point in general that’s not connected to anything internally. Who knows at this point.
During the final check, I discovered two errors.
The first one was I put a 510k resistor where a 10M should be. I think I know what happened here - I had a 10M there, but didn’t like the way it laid. I pulled it out, saw the blue stripe, and looked at the blurry schematic. I then assumed it was 510k and put that back in place. It’s been long enough that I forgot I actually bought 10M parts, so this was completely my fault.
The second was the b+ connection to the junction of R3/R4 wasn’t laid in. I remember looking at this and thinking I already had too much crap on the one tie point, and intended on going back later to put this in. “Later” just happened to be the last step, so this is both my fault and me claiming I meant to do that.
There’s still that hole in the front panel. I think I’m just going to go with my original thought and plug it.
But…that’s it! This device has been well used, looks like it’s Seen Things - that’s part of the charm of this device. It’s rusted and has spray paint on it and some scratches. It’s a piece of equipment that’s worked it’s entire life, and it’s ready to do it again. I’m not interested in “restoration,” I want the device to look like it does. So…crank up the 1KHz and let’s get some radios repaired!
Recapping the journey (and the device!)
Purchasing the unit at the 2023 Breezeshooters Hamfest in Butler PA.
It was obviously a kit unit.
Some cleanup on the physical parts of the device, then removing everything.
All the parts are out.
Putting things back in, one part at a time.
It lives!
And, we’re done.
The entire series from start to finish:
Purchasing the unit at Butler 2023: https://wereboar.com … fest-2023-butler-pa/
Initial evaluations on the device: https://wereboar.com … o-145-signal-tracer/
Part 0 - Some thoughts on parts inside: https://wereboar.com … ignal-tracer-part-0/
Part 1 - Collecting ideas and parts: https://wereboar.com … ignal-tracer-part-1/
Part 2 = Cleaning the device: https://wereboar.com … ignal-tracer-part-2/
Part 3 - Let’s get some parts: https://wereboar.com … ignal-tracer-part-3/
Part 4 - Some more prep work: https://wereboar.com … ignal-tracer-part-4/
Part 5 - Let’s take it apart: https://wereboar.com … ignal-tracer-part-5/
Intermission - Component notes: https://wereboar.com … cer-component-notes/
Part 6a - Starting the rebuild: https://wereboar.com … tarting-the-rebuild/
Part 6b - The power supply: https://wereboar.com … ng-the-power-supply/
Part 6c - Halfway there: https://wereboar.com … -to-run-a-few-wires/
Part 6d - We’re almost done: https://wereboar.com … art-6d-almost-there/
part 6e - The parts are in: https://wereboar.com … the-rebuild-is-done/
Part 7 - Check your work: https://wereboar.com … -checking-your-work/
Part 8 - And, it’s done: https://wereboar.com … art-8-and-were-done/
Wrapup - You’re reading it now.
It’s been over a year since that first evaluation, thank you for coming along on the journey. I think the next device will be the signal generator I picked up at the Scioto Valley hamfest. Stay tuned for more good junk, I mean equipment!
Previous part of this series: https://wereboar.com … art-8-and-were-done/
- 2024
- Oct
- 21
An Eico 145 Signal Tracer - Part 8 - And, we’re done.
This is the last part of the Eico 145 rebuild series. I’ll have one more post in regards to this unit, but that will be a wrap up and general thoughts on the rebuild process.
As in the previous post, I found a couple of mistakes in my work during the final check Those were corrected easily enough by adding a wire from the B+ point to the junction of R3/R4, and changing the 510k back to a 10M resistor. It turned out I did have the 10M resistors, and had ordered them.
I think what happened here is because I didn’t like the lay of the first part I used, I pulled it out. I didn’t pay attention and just grabbed a 510K because I saw the blue stripe. I’ll lay some blame on the blurry schematic, but most of the fault here lies with me. That’s why I checked my work.
The B+ line was a simple oversight. I remember running the rest of the B+ circuit and, because I had too many wires on one connection point, thinking to myself that I need to find a second tie point for the rest of the voltage. I didn’t do that. Again…checking your work is important. No matter how long you’ve done this kind of work, check it when you’re done.
The new 10M resistor gave me a chance to lay it in nicely.
I did put some other resistors in there for testing before I remembered the parts I bought specifically for this unit, specifically these two 4.7M carbon comp resistors that I just stuck out the side. Parts layout is important, as this gave a lot of hum:
Don’t do this. It made for a lot of noise, and it just reinforced the need for keeping your layout clean. Keep stuff short and close to the chassis. It did prove to me the device worked, however.
With that being said, all parts are placed.
I’m still not completely happy with the layout, but everything is soldered and tight. It’s not going anywhere.
Everything powered up with no issues. You can’t really see it as these devices don’t have much glow, but the rectifier on the left side has that tell-tale orange of the heater.
Put some labels on the back for posterity, and…
And it’s all done.
It still has some minor hum, but nothing like the whine it had with the 10M hanging out the side, and it’s a bit quieter than when I got it. I’m happy with the results, and I spent 10 minutes or so listening to some talking head on the crystal radio drone on about some topic that’s going to destroy everything or something, I don’t know.
There’s one more not-part of this series on the way where I wrap up thoughts and provide some things I’ve learned on the way to this point. Stay tuned, that should be ready to go later this week. That post will have links to all of the posts so you can easily start from wherever you like and read from there.
Stay tuned!
Final part of this series: https://wereboar.com … -and-final-thoughts/
Previous part of this series: https://wereboar.com … -checking-your-work/