Category: Amateur Radio

Posted on

Baby steps

I’ve been working a fair number of POTA stations lately – I have a Sapphire award for over 75 stations “hunted”. Woo-hoo! Not a big deal, really. Most have been FT8 or FT4 data modes, which I barely count as contacts. Going by the award endorsements, at least 20 have been phone, the rest data modes. Until today, I don’t think any have been CW. One of the reasons is that they’re almost always running 20 WPM or better – way too fast for me. I have, however, been working on a (temporary) solution for that until I get my copy speed back up.

The FT-1000 has an internal “contest keyer”, at least in terms of what qualified in the 90s and early 2000s. Yes, of course I have a few keyers around, but I kind of wanted to be able to use the rig’s internal memory keyer and dedicate my MK-1 to other radios. I bought a cheap-ass but working version of the Yaesu FH-1 remote key pad. The only difference between that the FH-1 is the button markings. Anyway, I set up one memory with just my call sign, and another one with the exchange – “TU 599 NE 5NN NE K”. Now all I need to do is listen to the POTA station’s call sign a couple of times to get it all, and I can use the keyer to send what I need to.

I worked N2DA on 20 meters this afternoon, and got my first CW POTA contact in the log… and my first CW contact using the Mark V FT-1000.

Posted on

An Embarrassment of FT-1000s

I’ve been scouting for a replacement for the TS-850 for a while now. Something maybe a little newer, but not one of the new rigs that puts most of the functions on a screen. Call me old, I like my knobs and buttons. I don’t like wading through menu layers to get to stuff I change fairly often. I never did fall in love with the TS-850. It’s a fine rig and all… but it replaced a TS-930S, and while I appreciate the relief from the constant power supply issues, the receiver never has really measured up. I know that’s a high bar to set.

At first I was thinking about the FT-1000 series, Yaesu’s flagship contesting radio from the late 90s through the mid 2000s. The original FT-1000 and FT-1000D was superseded by the FT-1000MP, and then by the Mark V in two different flavors – the 200W Mark V FT-1000MP, and the 100W Mark V FT-1000MP Field. Nice radios, but they’re all 20+ years old. I also considered the Kenwood TS-590SG, a much more modern, DSP based rig. Then there’s the Elecraft K3. A new K4 is nice, but at nearly $7K it’s just not in the cards. the K3 is highly regarded and falls somewhere in the $1500-2500 range, depending on the many, many options and filters available for it. I thought about the TS-950SDX, but pretty much nobody recommends that – it seems like a continuation of the 850 with audio DSP. 

I’d pretty much decided on the K3, albeit a little reluctantly. Some of the functions seem a little more menu driven than I’d like, but it’s pretty much universally loved. I hadn’t pulled the trigger yet, waiting on a deal I liked. What I wanted would cost me over $1K, probably closer to $2K, and I wanted to find the “sweet spot” of all the options I wanted, but at a good price. 

Then someone listed an FT-1000MP for $600, all in, shipped to my doorstep. I just couldn’t pass that up. I bought it. It arrived. I fixed one problem – a dead CAT serial port that took a $1.30 chip to fix. It’s awesome, I love it. It exceeded my expectations. I used it for SSB, for FT8, even some CW. Life was good. Sure, a Mark V Field would be nice, but I was happy.

Then someone listed a Mark V FT-1000MP – as-is, for $200. Wait, what? He was up front about his reasons. He’d had some problem or other, fixed it, everything worked until he closed up the front panel, then the buttons and LEDs quit working. He took it apart again, found a cable loose or something, closed it up, and still had a dead front panel. He decided to call it quits and sell. Well, I’d just been in the front panel of an FT-1000MP – nearly identical – days before, and encountered a very similar problem that turned out to be knucklehead me not recognizing the “zero insertion force” (ZIF) flat cable connectors, and getting a couple of them partially seated. On those connectors there’s a latching piece that has to be pulled out to seat the cable, then pushed in. These things were designed to be assembled by tiny little Japanese girls in a factory, not mucked about with by my giant ham fists. I figured I could fix this $200 rig and have an updated, newer, fancier version of what I had just fallen in love with. So I bought it.

The UPS boxes arrived yesterday. The rig has its own power supply; the 200 W final amp needs a 30 V supply, so it comes with an FP-29 switching 12/30 V power supply. I put it in the bench and, sure enough, the display was OK (if a bit dim) but the buttons and LEDs were unresponsive. It did take longer than I thought to get it working, but in the end I did. It wasn’t a flat cable; it seems to have been just the routing of the high-voltage wires for the display’s CCFL backlight tube. Last night I put it on the air, and I have to say, the upgrades to the original MP are pretty impressive. I don’t know that I will even need to move the extra IF filters I bought for the first rig over to it.

So, now my tiny operating desk has a TS-850, and above it a shelf with an FT-1000MP and a Mark V FT-1000MP stacked on top. A little overkill, sure. And yes, I’m sure I’ll sell two of these rigs. I had been keeping an eye out for a Mark V Field, the 100 W version, because my remote antenna tuner is rated for 125 W maximum, but as it turns out the 200 W Mark V has a convenient menu setting to set the maximum output power to 200, 75, or 10 W. It also has the typical 100/50 W switch inside the rig, same as the TS-850 and the older FT-1000MP, but I don’t know what that will actually do on this rig. I have the radio set for 75W max. Is it perfect? No; it has one mismatched knob from a different Yaesu rig that isn’t obvious but I’d like to replace it some day. It’s pretty nice cosmetically, though, and seems perfectly functional. I spent an hour exploring different features, some I’ll use and some I may not, and there are still some I haven’t tried out. The transition from the older rig to the Mark V is almost as different as going from the TS-850 to the FT-1000 was.

If someone had told me a year ago that I’d have a stack of radios like this on that desk, I’d have thought they didn’t know me very well… but when things line up, they line up, and here we are. Now I just need to get the 850’s ALC issue fixed so it’s working properly again, and get it listed for sale. Then I’ll pull the filters from the FT-1000MP and list that one, along with a few other pieces of gear I don’t need. Meanwhile, I’m exploring a newfound enjoyment of chasing POTA stations and finding new DX countries on FT8 and FT4.

Posted on

It’s New Radio Day!

Woohoo! It’s always an adventure to un-box a new radio. In this case it’s “new to me”, but qualifies as “vintage” or “classic”, I guess. I picked up a Yaesu FT-1000MP, manufactured in 2000 – so, 26 years old. That makes it a late production 1000MP, made just as the successor Mark V FT-1000MP was introduced. This was Yaesu’s flagship HF contesting rig at the time, retailing for $2500 in 2000 – which would be just a bit under $5000 in 2026 dollars. It was pretty advanced for the time, with dual receivers, DSP in the audio chain, and quadruple conversion. These were a huge hit with contesters, and the price on the used market has fallen well under $1K for a clean example with no defects.

The radio arrived yesterday from a ham in Wisconsin. I unboxed it and gave it a quick bench checkout to make sure there were no major issues. Aside from a little dent in teh top speaker grille – easily corrected once I have the top cover off – there are no cosmetic issues with it. The display isn’t quite as bright as I’d like to see, but it’s adequate; these old CCFL backlit LCDs are aging out and will all eventually fail. Fortunately, replacing the backlight with an LED strip is neither difficult nor expensive. I did it to my TS-850 last year.

After setting it up on the operating desk, I did some side by side comparisons with the Kenwood. Both seem to have about the same sensitivity; I could copy both stronger and weak signals on both rigs with essentially identical readability. That shouldn’t have been a surprise, really — the TS-850 was no slouch for its day, either. I switched both rigs to the 500 Hz CW filters. The Kenwood’s is an optional crystal filter I had to buy and install, the Yaesu has one installed in the second IF (8.215 MHz) from the factory. It was pretty obvious that the FT-1000MP was a little better – again, both were clear and readable, but there was a little less noise on the Yaesu, and it was less tiring to listen to. Later I figured out that I didn’t have the DSP switched on at the time; turning that on makes it sound even better.

I’ve spent a little time exploring how to use the rig. It will take a while to learn all of the features and functions, but there are already a coupe that surprised me. It doesn’t surprise me that there is a sub-receiver, obviously. I figured that was handy for contesting, but didn’t really see how I’d use it during casual operating. I was surprised, however, by how quickly I figured out that yes, it is nice to be able to tune around listening for other stations without changing your operating frequency. It’s so quick and easy to just hit the “dual” button to get both receivers in the headphones.

Tuning the RT-11 remote tuner is pretty quick and easy… though it will be even quicker and easier when I have a remote keypad plugged in (Yaesu FH-1 or FH-2 or equivalent). That has a dedicated button to put out a carrier at a selectable 10, 25, or 100W power level for just this purpose. For now, I turn off the internal tuner and the keyer, set the RF power control to about 12 o’clock, and key the rig with either paddle. That puts about 25W out to the antenna. When the RT-11 finishes I turn on the rig’s tuner, hit the TUNE button, and while it’s doing its thing turn the RF to max and turn the internal keyer back on. The whole process takes only a few seconds.

So far the only glitch I’ve found is a non-working “A->B” button. This is the one that copies the main VFO frequency to the sub VFO. I do miss that function and I’ll need to fix that button. I’m hopeful that Yaesu used standard tactile switches for the panel and not some dome switch pad. Over the next few days I have some things planned that will require taking the overs off, so I’ll have a look then. (note: This turned out to just be me not knowing that you need to press and hold the button.) On the schedule for this rig:

  • Install the 250 Hz CW filter that I have coming on Monday
  • Install the TCXO-4 module that should arrive today
  • Replace the internal backup battery
  • Check out the front panel buttons to see about fixing the A->B button
  • Get a look at the display and see whether I want to install an LED backlight kit, or DIY a solution
  • Buy or build a remote keypad – this will give me a single TUNE button as well as the ability to use the two 20-character and four 50-character CW keyer memories

I’m pretty happy with the rig. It’s impressive looking – about three inches wider than the TS-850, all of that extra space packed with knobs and buttons. We hams just love knobs and buttons! I like the way it sounds; I like the fact that it’s AC powered so I can remove one power supply from the desk. I’ll operate it for a while before deciding whether to buy any additional filters for it. The factory complement includes 2.4 kHz SSB and 500 Hz CW filters for the main VFO. There are also are are 2 kHz SSB and 250 Hz CW filters for the second IF available, plus 2 kHz, 500 Hz, and 250 Hz for the third IF and 500 Hz for the sub receiver. Filters are not cheap; I want to see what the IF shift & width controls and the EDSP will do before deciding what (if any) I want to install other than the 250 Hz 2nd IF filter I already have coming.

I’ve called CQ a few times, but there are at least two separate contests going on – one SKCC and one not. I did have one guy answer but he disappeared, so no complete QSO yet. I’ll keep trying. With the keyer set at 10 WPM it shouldn’t be long before I’ve got a couple in the logbook. I am intentionally holding off on ordering cables for the Digirig Mobile; I want to stick to CW and phone for a while.

Posted on

It’s always something…

The other day I took the TS-850 apart, once again. For whatever reason (more about that later), I was only getting about 50W output on any band in CW mode. I did the ALC adjustments and got it stable at 100W where it should be… and along the way, figured out that it may have been “operator headspace” all along. There’s a CAR (carrier) control that I was suing to set the power, and also a “PWR” (power level) control that, honestly, I’d forgotten was there. I may have had it set to a lower level. Who knows? It’s working now.

I’d had to disassemble a substantial part of the “shack” to get the TS-850 set up on the bench. I had to un-cable the radio, pull the power supply, then unhook the Heathkit HM-102 power/SWR meter and the dummy load. In order to do that, I had to de-cable and move the Heathkit SB-101 and its companion SB-600 speaker cabinet with the speaker and power supply. Those sit on a shelf that I built that sits over the top of the TS-850 and some other gear. It really is kind of a major operation to take something out of the operating position desk, which is something I hope to remedy sooner or later with a bigger, roomier desk.

I got everything done – the power output back up to 100W and I re-installed the TCXO that I’d pulled for some reason a few months ago. I buttoned everything back up and spent the better part of an hour getting all of the gear re-installed and cabled. While I had it all apart, I decided to re-do the cabling. I have the antenna and the dummy load on an A/B coax switch, the input of which is connected to the HM-102, which is itself connected to the SB-610 station monitor. In order to switch from one rig to another I had to un-screw that rig’s antenna coax at the input of the SB-610, and connect the other’s coax. I decided to install the MFJ 6-way coax switch to all of the radios, and connect that tot he SB-610 to make it quick and easy to switch rigs. I wall mounted both coax switches and got everything cabled up, double-checking the connections as I went.

That evening I wanted to try some CW contacts with the SB-101. After tuning into the dummy load, I switched to the antenna and called CQ several times. I could hear a few other stations up and down a couple kHz from where I was, but I had no replies. I decided to switch to the TS-850, so just flipped the 6-way switch to position 1 and tried transmitting. The Kenwood showed no RF out – none. Even with the CAR and PWR turned to the max settings, nothing at all. Somewhat discouraged and more than a little irritated, I shut everything off and went upstairs.

The more I thought about it, the less convinced I was that both rigs had failed at the same time. I decided that I must have messed up the coax cabling, or had a bad cable. I went back down and did some troubleshooting. Starting with just the dummy load on a short coax jumper, I tested the TS-850 – full power out, no problem at all. I then went through the whole chain, connecting the dummy load at each junction and testing for power output. The 6-way coax switch tested good. Then the SB-600 – good. Then the HM-102 – good. Then the 2-way coax switch – Nope! No output.

That switch, an old MFJ-1702 that I’d picked up use years ago, has failed. THere’s nothing apparently wrong with it mechanically, I took it apart and checked for broken, corroded, or misaligned parts. It tests fine with an Ohm meter, no shorts or opens in either position. It does not, however, work with either radio in position A (the antenna) and intermittently fails in position B (dummy load).

Given its age and all, I decided not to try and troubleshoot or fix it. It’s going into the trash, and I’ll replace it with a good quality Diamond CX210A. It’s more expensive than the many options I see from Diamond, Opek, and many others including a slew of no-name Chinesium garbage that all look identical to the MFJ I’m replacing. In the mean time, I’ve connected the antenna coax directly to the HM-102.

Oh, and the reason for the low output on the TS-850? I’m honestly not sure. I suspect, however, that I simply forgot that there is both a CAR control for the carrier level in CW, AM, and FM modes, and a PWR control that is global in nature – it works in all modes, regardless of the MIC or CAR settings. Given that the most I’ve been able to get out of the rig while working FT8 without the ALC kicking in has been between 50 and 75 W, I suspect I may have just inadvertently had the PWR control set to the point where it limited CW output to 50 W. I really don’t know for sure, but I suspect that’s the root cause. Hey, at least I discovered the failed switch now rather than having it intermittently fail over some period of time and potentially cause more problems.

Posted on

The New Shack

I realized I haven’t posted anything since early this year when I struggling with equipment located upstairs and all of the RFI and other issues that caused. Since that time I’ve made a good deal of progress.

All of the radio equipment is now in the basement. It’s not idea as far as I’m concerned, but it is what it is. From a practical standpoint it makes sense. I can get coax straight out the back of the house, which makes grounding and antenna installation so much easier. It’s unfortunate that everything is crammed into a very small space. It’s a little built-in “nook” probably intended for study or something. A 51″ wide countertop, 24″ deep (if that); wall cabinets mounted above so it’s a little constrained both horizontally and vertically. A couple of duplex outlets, a phone jack – no Ethernet, and no way to get it there either. Doing any kind of wiring would require major demolition and construction. Just getting RG-8/U and a flat cable for the remote tuner control into that space took a lot, and I do mean a lot.

The antenna is now a 135′ (give or take a little) loop in a triangular shape around the back yard. The feed end is at about 16′; the two legs go out to two maple trees where the wire is up between 25 and 30 feet. Again, not ideal, but it’s what I could manage to get up in the air. A 1:1 balun at the feed point connects the antenna to 50′ of LMR-400, which connects to an LDG RT-11 remote tuner, and from there to the shack via about 35′ of RG-8/U.

I’ve successfully run 100W+ on SSB and CW with no interference with anything else, no RFI in the house, no issues with breakers. The RT-11 doesn’t match the antenna in all cases; on most bands I need to also use the TS-850’s internal tuner. Surprisingly enough, I’ve worked a couple dozen countries using 25 to 50 W on FT8, and one night worked a couple of Russians (grids LO02 and LO33) on 20 meter SSB. Log entries show that 40 meters is almost all US and a smattering of Canadians, with a few surprising exceptions – Japan, Spain, and France. I attribute those to guys in those countries with good beam antennas! Not surprisingly, the higher in frequency I go, the better the DX results are. I’ve even worked a few US stations on 80, but of course that’s pretty clearly NVIS so I don’t even try much.

I have the TS-850, SP-31, FT-817nd, the keyer, and a couple of Astron DC power supplies on the desk. I built a shelf for the SB-101 and SB-600/HP-23. On the other side of the desk is an SB-610 monitor scope I picked up, an HM-102 power/SWR meter, the control for the RT-11, and a coax switch to switch between the antenna and a dummy load.

I am planning a new shack, though. I’m slowly cleaning out my basement workshop and storage area. My plan is to revamp the storage area with nicer cabinets, and build a 6′ long operating desk about 30-32″ deep in one corner. A 4′ workbench will go next to that. I’ll have room for everything, and more room for a straight key and paddle in a more comfortable operating position. Right now things are a little cramped.

I’ve worked a lot more FT8 than I would like to admit, but I’ve also worked some SSB, one SSTV QSO, and even a PSK and an RTTY contact. RTTY and SSTV were firsts for me. None of those are confirmed; the RTTY and PSK contacts got lost in QSB but the SSTV was solid. I just wish I’d saved the darned image, I’m really bummed that I lost that. I blame the software.

Anyway… onward.

Posted on

RFI from the shack, again, naturally

The other day I decided to try setting up the SB-101 and do some testing of the setup with the antenna tuner. As I tuned up with a few watts, things were OK… then I turned up the drive past 50 W, and things got wonky. The monitors on the PC flickered, the PC beeped, it logged me out, the CO monitor in the hallway beeped, and a few minutes later I noticed we’d lost our Internet connection. After a little investigation I found half a dozen GFCI/AFCI breakers in our main panel had tripped and had to be reset. It had dropped power to the entire kitchen, so the router was powered off.

Obviously there’s an RFI problem. I have all of the equipment grounded to a new copper bus bar using 12-18 inch flat copper braid, and the bus bar is grounded to the household AC ground. Ah, there’s the mistake. That puts any stray RFI onto the house electrical ground, which the breakers interpret as a grounding problem.

The shack is on the second floor for the time being, in the “spare” bedroom that has been my office for the past 15 years or so. I’m using a 71′ long end fed wire, with about 18′ or so of counterpoise. I’m feeding it through an MFJ tuner, but that means there’s a good deal of RF on the feedline inside the house before it snakes out through a window.

The eventual solution will be a remote auto tuner at or near the feedpoint of the antenna, outside and well away from the house. The interim solution? Limit my output to QRP levels. I can work some SSB with normal power, but CW or digital modes using much more than that is a recipe for electrical problems. It’s less than ideal, but once our new deck is built I should have a good mounting point for a remote tuner, and a feedpoint from which I can string up a full wave loop for 40 meters that should work pretty well on most other bands too.

Posted on

SB-101 Dial Drive Overhaul

When I bought the Heathkit SB-101, the dial drive was a mess. The dial itself, of course, was old and severely cracked. Much worse, though, was that FedEx had dropped the rig on its face – and even though it was bubble wrapped, whoever packed it didn’t bother to put Styrofoam blocks between the knobs. That would have protected the face and knobs, but as it was the main tuning dial was damaged. The aluminum skirt was bent, and the drive pulley was damaged.

The drive pulley consists of a pair of bronze washers, each with a rolled bead near the outer perimeter, which are spaced slightly apart using a tiny aluminum spacer. That assembly grips an aluminum drive ring that’s attached to the plastic dial. The raised beads put pressure on the drive ring to turn the main dial. Well, on mine, one of those bronze washers is cracked and bent. I was unable to get it sufficiently straightened out to give a solid grip on the tuning drive ring all the way around, so the knob would slip on the dial. Of course no replacement parts are available anywhere, other than from a parts rig – which I don’t have.

With nothing to lose, I decided to try something new. I got the damaged washer as straight as I could, then grabbed a 2 x 5 mm silicone O-ring left over from a coffee machine repair. I put that around the spacer in between the bronze washers and reassembled the mechanism. Success! The operation was now smooth, positive, and free of the slippage I’d experienced before.

Left to right: The shaft and outer drive washer, crack visible at about 11 o’clock. Next is the middle spacer, inner washer, end spacer, and the screw that holds it all together.

After a few days of use, however, I noticed some slipping again. I suspected there was a little oil or grease that had migrated to the O-ring, and I was right. I pulled the assembly apart and thoroughly cleaned everything with some 91% isopropyl alcohol and paper towel. When I re-assembled it, I used a #009 neoprene O-ring. It’s very close to the 5 x 2 mm O-ring I had in there before, but I was hoping that the very slightly smaller cross section and the neoprene material might give a little more traction. I also used a Q-tip with a little alcohol to clean off the dial drive ring, in case there was oil or aluminum oxide on that.

The middle spacer and inner washer, with the silicone (red) and neoprene (black) O-rings.

With everything back together, I once again had smooth, positive drive with no slipping. Time will tell how well this fix holds up, but it’s definitely better than the nearly unusable state in which I received the rig.

The new O-ring in place around the center spacer before re-assembly

So far the tuning dial has worked out OK. If it fails, I have a vague plan for a 3D printed center hub for the dial with a ring gear, and a pinion gear for the dial shaft. I understand why this might be one reason the HW-100 is more popular than the SB-100/101/102, but this may also help some owners of other SB-line gear like the SB-300/302 and 400/401.

Posted on

SB-101 Troubleshooting, Part 3

After getting some really good advice from the Heathkit Radios group, I did some further troubleshooting. I re-soldered much of the RF driver board, having found a spot that would change the symptoms when it was hit with freeze spray or tapped with a wooden probe.

At one point, I just got curious as to what the SSB performance was like compared to CW. Surprise! In SSB mode, I could key the mic and get pretty good output. That told me the problem was limited to CW and tune mode, which pointed only one place… the mode switch! I had cleaned that switch at least once before, but I did it again. A squirt of the nearly depleted can of Radio Shack tuner cleaner, a dozen or more rotations in each direction, and … yes, now it’s working.

After completing the transmitter alignment procedure, I put the whole thing back together (mistake, as it turned out) and took it all upstairs where I have my other rigs. I tuned the TS-850S to WWV and zero-beat the 100 kHz calibrator as closely as I could. Then I figured out that i really needed to move the dial pointer on the LMO shaft. Remember how I said I’d put everything together? It’s a real bear trying to get at the set screw to make that adjustment when it’s in the cabinet. I managed, but I may have used a word that I would not repeat on the air.

With all that done, I resorted to a sked and had a nice chat on 20 meters with Dan, W7RF. I was tuned up for close to max output, and got a good report for audio and signal strength given my little 70′ wire in the trees in the back yard. The rig is now officially “in use”!

Posted on

SB-101 Troubleshooting, Pt. 2

The previous work got me thinking. The LMO problem was, apparently, flaky rivets at the RCA connector; I peened those and the instability went away completely. The scratchy noise in the audio was fixed by generous application of desoldering braid and fresh solder on the audio board. And, whereas I was seeing only a few mV of RF at the output side of T1 (the balanced modulator output transformer), after again re-soldering a few points I’ve suddenly got close to the expected level – about 260 mV peak. No real explanation for why it suddenly jumped from 25 to over 250 mV. All of this points to bad connections and oxidization.

Now onward. V3 is not amplifying as it should. I get about 150-175 mV peak RF out of pin 5 (the plate) where it should be around 7 V. I swapped V3 with V4, then V2 & V3 with V10 & V11, since they are all the same 6AU6 type. Of course that didn’t make a difference. I’m not expecting to find bad tubes. What I suspect is happening is that there is old flux contaminating a number of solder joints. After sitting idle for decades, there is now oxidization that is getting disturbed by heat and motion. That’s causing these marginal or bad solder joints to rather randomly manifest themselves. The solder joints all look OK; most are not terribly pretty, as I would expect with a Heathkit, but solid. It’s telling, though, that de- and re-soldering is fixing so many issues. I decided to simply go through and de-solder, thoroughly clean, and properly re-solder every joint I could get to on the IF, bandpass, and driver boards.

I also had a very flaky meter zero potentiometer, and if it’s bad then the carrier null is probably not far behind. Of course you can’t buy direct replacements for the originals, so I bought some new top-adjust 10 turn trim pots. One of them fixed the meter zero issue quite nicely, and I’ll replace the carrier null pot when I have time.

Unfortunately none of the work I have done has had the slightest impact on the RF output. It’s still next to nothing. About 1W or less on 80 meters, and maybe 10 or 12 on 10 meters. I’ve asked advice on the Heathkit radios group (here) and and working with a couple of guys who understand tube circuits better than I do to troubleshoot.

Posted on

SB-101 Troubleshooting

Wow, what fun we’re having!

This rig has been one problem after another. After I got all of the bad resistors replaced, a new problem occurred. No or close to no RF output. I can coax a watt or so out of it on 80 meters, maybe 5 W out on 10 meters. My troubleshooting efforts were hampered by the fact that while I could probe around all I wanted with an O-scope or meter, nothing in the manual gave any indication (at least none that I could find) of the expected RF signal levels in the path – the carrier oscillator, VFO, etc. So I could see the carrier oscillator was producing about small fraction of a volt peak to peak, but I had no idea if that was right or not (but it seemed awfully low to me).

Here’s where the folks in the Heathkit group at groups.io really were helpful. It turns out that the schematics printed in the manual for the Heathkit HW-101, which is nearly identical to the SB-101, do indeed show expected RF signal levels at numerous points in the circuit. Armed with that information, I confirmed that at least part of the problem was a very low signal from the carrier oscillator. In an effort to double-check my work, I went back and re-checked every part I had replaced – after which the oscillator signal was fine (more or less). That told me there was a physical problem. It could be bad solder joints, bad ground, a cracked board, or a cracked part. Just poking around with the meter probes had changed things.

After much trial, tribulation and scope work, I spent some time de-soldering and re-soldering most of the modulator circuit board. That seemed to stabilize the carrier oscillator in a working state. I had to do the same to the audio board to solve a newly developed scratchy intermittent noise issue that appeared. Along the way I discovered a bad connection to the LMO output RCA plug. Then the LMO started randomly jumping 1, 2, or maybe 10 kHz whenever it was tapped or touched. I ended up peening the two pop rivets holding the phono jack in the back of the LMO to fix that one.

Now at least I’m back to having a relatively stable, quiet rig with a fixed symptom I can chase. That symptom is a good signal from the carrier oscillator reaching the balanced modulator, a relatively normal signal at the input to the modulator transformer, and not much of anything coming out of that transformer. Right now I’m feeling a little foolish because I had that transformer out of the radio this morning, opened it up, re-glued the coil form to the base, checked that the wires were still attached to the pins… and did not check the windings for continuity. What a rookie move. I’ll check that in the morning.