Listen to Latest SolderSmoke Podcast

Thursday, October 15, 2020

Too Simple? Deficiency of the Lafayette HA-600A Product Detector?


I've been having a lot of fun with the Lafayette HA-600A receiver that I picked up earlier this month.  Adding to the mirth, I noticed that on SSB, the signals sound a bit scratchy, a bit distorted, not-quite-right. (I'm not being facetious;  this is an interesting problem and it might give me a chance to actually improve a piece of gear that I  -- as a teenager -- had been afraid to work on.) 

Before digging into the circuitry, I engaged in some front panel troubleshooting:  I switched to AM and tuned in a strong local AM broadcast signal.  It sounded great -- it had no sign of the distortion I was hearing on SSB.   This was an important hint -- the only difference between the circuitry used on AM and the circuitry used on SSB is the detector and the BFO.  In the AM mode a simple diode detector is used.  In SSB a product detector and BFO is used.  The BFO sounded fine and looked good on the scope. This caused me to focus on the product detector as the culprit. 

Check out the schematic above.  Tr-5 is the product detector.  It is really, really simple.  (See Einstein quote below.)  It is a single-transistor mixer with BFO energy going into the base and IF energy going into the emitter.  Output is taken from the collector and sent to the audio amplifiers. (A complete schematic for the receiver can be seen here: )

I had never before seen a product detector like this.  One such detector is described in Experimental Methods for RF Design (page 5.3) but the authors devoted just one paragraph to the circuity, noting that, "We have not performed careful measurement on this mixer."  The lack of enthusiasm is palpable, and probably justified.  

A Google search shows there is not a lot of literature on single BJT product detectors.  There is a good 1968 article in Ham Radio Magazine:      It describes a somewhat different circuit used in the Gonset Sidewinder.  The author notes that this circuit has "not been popular." 

To test my suspicion that the product detector is the problem,  I set up a little experiment.  I loosely coupled the output of a signal generator to the IF circuitry of the HA-600A.  I put the sign gen exactly on the frequency of the BFO.  Then, I switched the receiver to AM, turning off the BFO and putting the AM diode detector to work.  I was able to tune in the SSB signals without the kind of distortion I had heard when using the product detector.   

So what do you folks think?    Is the product detector the culprit?  Or could the problem be in the AGC?  Should I start plotting a change in the detector circuitry?  Might a diode ring work better?  

Monday, October 12, 2020

Quino, The Creator of Mafalda ("BASTA!") RIP

Putting "Basta" in the SolderSmoke search box yields many blog posts.  The cry of ENOUGH! from six year-old Mafalda has been part of the podcast for many years and is now part of the SolderSmoke lexicon.

We don't do a lot of obits on this blog (we try to keep it all upbeat) but the passing of Mafalda's creator Quino is news that many of you may have missed, and that I think merits mention here.  This link has a nice 3 minute report from NPR:

Adios Quino. Gracias por todo. 

Sunday, October 11, 2020

Ryan Flowers' Admirable Approach to the BITX40 Module


We must remember that Farhan designed the BITX transceivers -- and especially the BITX40 Module -- in the hope that these rigs would encourage hams to tinker, to modify, to change and to repair.   When I read Ryan Flowers' blog post, I thought that Farhan's mission has been accomplished.

I was also struck by how nice it is that Ryan has a sentimental attachment to this BITX40 module because it was a gift from his wife.  That's the kind of thing that gives a piece of electronic circuity soul. 

Above we see Ryan's module with many of the parts removed in the sections that he feels he messed up.  This is obviously a good approach, but it reminded me of the nightmare I've had (and I am not the only one) where, in frustration, I take ALL the parts off a recalcitrant board.  

Stick with it Ryan!  You are on the right track.  And it sounds to me like you WILL soon be homebrewing from scratch your own SSB transceiver. 

A while back we built a blog with many nice mods for the BITX40 Module:

Saturday, October 10, 2020

Chip Replaced, GSC 6000 Counter Fixed


This thing has been half-broken for a long time.  I needed to get the input for 40 MHz - 650 MHz working    I got the a replacement SP8630B Plessey divide-by-ten counter chip on e-bay, and yesterday I extracted the old chip and put in the replacement.  I took great care NOT to solder this one in upside down (as I had done with another chip replacement in this counter). I used solder flux and solder wick to gradually get the pins free of the board. (You can see the old chip in the picture above.)

As to what happened to the original SP8630B chip,  John over on the Vintage Test Gear Facebook page wrote: 

The Plessey SP8630A/B is an ECL divide by 10 prescaler, with a upper working frequency of 600MHz. That generation went out of production in the late 1980s. Plessey was bought by a Canadian company now called Micrel. You may be able to find one from one of the specialist obsolete component companies, but it may be dead on arrival. Those ECL ICs had a fairly high mortality rate if they are very old.

It is the old story of "metal migration". In early semiconductors very small impurities in the silicon structure cause minute bits of the metallisation to leach out into the essentially non-conducting silicon insulation. Many old devices, although they have never been used, were found to be very leaky and this degrades the gain of the active devices. The worst types are the very old Germanium transistors.

As the semiconductor scientist learnt more about the super cleanliness required and the better purification of the metals the problem tended to improve. The Marconi company I worked for back in the 1980s had a real problem with comms satellites failing after a few years of service. Of course you can't go up there and swap out the faulty devices. Accelerated ageing of a backup satellite showed that some devices just stopped working after being subjected to high and low temperature cycling, which is a common problem with satellites in orbit!

I am liking this little machine more and more.  It is very simple -- no microcontroller, just a collection of gates.   I discovered that the main main crystal oscillator is actually built inside a little oven to keep the temperature stable -- oscillator and the oven stay on as long as the counter is plugged in, even when the device is switched off.  I calibrated the counter with WWV and with my HP8640B and with my little Feeltech sig gen counter.   I wish I knew how to calibrate the counter in the Rigol DS1102E oscilloscope.  

Friday, October 9, 2020

The Bitsy -- Homebrew Double Sideband from Scotland


This is such a beautiful project:  it involves DSB, homebrew, troubleshooting, George Dobbs, SSDRA, J310s, a box kite,  and ham radio nostalgia.  I was struck by how similar the Bitsy looks to some of my own DSB creations (but the Bitsy is nicer).  I'm really pleased to find a DSB project coming out of the UK -- when I was there, DSB was kind of frowned upon by spectrum preservation zealots.  I say there is plenty of room for the very few homebrew DSB rigs that will ever grace the airwaves with their presence.   Thanks John.  Have fun with all your projects.  73  Bill 

Hi Bill

In the early 80's I built and experimented with Direct Conversion Receivers and had a lot of fun with them. I came across a 40M DC cw transceiver by the late Rev. George Dobbs in a Practical Wireless magazine and decided to build it. Whether I was just lucky I'm not sure but it worked first time and I had several cw contacts with it. It was called “The PW Severn”. I then discovered DSB and looked into modifying the wee rig. I gave George a phone, no internet in those days, and explained what I was proposing to do and if there was any advice he could offer. His reply was ,  “it should work so try it and see, any problems get back to me”. It worked and I had a lot of fun with it. I used to take it portable and with a box kite to support a long wire and worked all over Europe.

It was after reading and learning about circuits and home brewing I wondered if I could design and build a DSB transceiver of my own. I had plenty of articles and most importantly a copy of Solid State Design, now well thumbed.

So the “Bitsy” was born. It is an 80M DSB transceiver. The PA produces about 2 watts. I took what I thought was the best for each module and built it using six circuit boards which I designed and etched myself. Nowadays I use the Manhattan method for one of circuits. It is much easier and quicker.

Like most home brew projects, the fun is in the building and the wee rig lived in a box for several years. Probably over 30. My doesn't time fly. I came across it again while looking through my boxes and decided to give it an airing. Expecting it to work on power up I was quite shocked when it produced nothing on both receive and transmit. After staring at it for a couple of minutes I unscrewed the lid and studied the wiring for a dry joint. Nothing so I switched on my Digital Multimeter and Oscilloscope. I soon found out that the output from the VFO was missing. The VFO uses one FET and two PNP Transistors for the buffers. The scope soon proved that the FET was faulty. I used an MPF102. These are hard to get so I replaced it with a J310. While I had the VFO out I also replaced the 9.1v zener diode, which provides a regulated voltage for the FET, with a 78L05 connecting the centre pin via a 580ohm resistor to earth. This gives me a 9.3v regulated supply for the oscillator. It is now back in full working condition.

With the Covid 19 epidemic I, like a lot of the Amateur Radio fraternity, am spending a lot of time in the shack and looking for new projects. I am buying back my old FT200 which was my first rig. An old friend and lapsed amateur has still got it and agreed to sell it back to me. It is still in a good condition for being nearly 50 years old and just needs some TLC. When it is finished it will take pride of place beside my restored Heathkit SB104A. And they say nostalgia is not what it used to be!!

John Forsyth


Thursday, October 8, 2020

HA-600A Gets a New Coat of Paint -- After Almost 50 years!


The HA-600A that I picked up last week was looking kind of sorry.  There was a lot of rust on the cabinet.  Below is the before picture. 

I'm not really into cabinetry or radio aesthetics, but it is amazing what a 6 dollar can of spray paint can do. Formula 409 also helps. I moved the light bulbs forward a bit to get more light on that Juliano Blue dial. 

I am really enjoying this radio.  It has brought back many memories.  I think I got one for Christmas in 1972.  I was 14.  I got my Novice ticket on April 27, 1973 and made my first contact on July 19, 1973.  For that first contact I was using an HA-600A and a Heathkit DX-40.  Later I used the Lafayette with a Heathkit DX-100.   The HA-600A was replaced by the far superior Drake 2B on April 11, 1974.  So I used this receiver for more than two years.  

Looking around inside this receiver (and following up with Google) I learned some more about it: 
-- It was made in Japan. 
-- The manual says it has a "mechanical filter" but in fact it has a Toyo ceramic filter.  This may have been just an honest mistake by the folks who wrote the manual -- maybe they didn't understand the difference between the two types of filters. 
-- There is a big difference between the HA-600 and the HA-600A, mostly in the front end circuitry.  The HA-600 has fewer amplifier circuits at the front end.  This probably explains why the HA-600 I picked up did not seem to live up to my memories of my teen-year HA-600A.  

The fellow who gave it to me tells me that it had belonged to the short-wave listener father of a friend of his. 

I know we have a lot of tube-type receivers that are much older than this thing, but I still think it is pretty amazing that this is a receiver that I used almost half a century ago.  And it is still as good as new.

Wednesday, October 7, 2020

Solar Cycle 25 - The Gleissberg Cycle Dashes Hopes for a Big Solar Max


In our last podcast Pete N6QW expressed pessimism about Solar Cycle 25.   I pushed back, asking Pete to stop with the negative vibes.  Well, as always, it turns out that Pete was right. 

Hack-A-Day today has a nice post about solar activity.  They note that cycle 25 is likely to be much like cycle 24 -- not great, certainly not as great as cycle 19.  Pete operated during that magnificent event -- I was born during cycle 19 -- TRGHS.  

While Pete was right about the poor prospects for cycle 25, I doubt that he knew WHY it will be so tepid.  Well friends, here is something else for us to worry about:  THE GLEISSBERG CYCLE.  This one is not 11 years long.  It is 87 years long and we are in the declining phase right now. So apparently it will be future generations of ham radio operators who will experience sunspots like those of 1959.  Curse you Gleissberg cycle!  

But I suppose it is better to light one candle than to curse the darkness.   Cycle 25 maximum is only about five years away.  So I'm thinking of rebuilding my Moxon.   Or maybe getting a Hex beam... 

Tuesday, October 6, 2020

TRGHS -- My First SW Receiver Offered FREE for Pickup -- The Lafayette HA-600A (Looking for Globe VFO Deluxe)


So on September 27,2020,  I was sitting quietly in my shack, perusing the postings on various radio-related Facebook groups, when suddenly I saw it:  my very first shortwave receiver, the magic box that had put me firmly on the path to amateur radio, the Lafayette HA-600A.  Joe, the owner,  was offering it FREE to anyone willing to pick it up at his home in Virginia's Shenandoah Valley.  Holy Cow!  I was scheduled to drive through that very valley later that week.  A message was sent and the deal was done.  CLEARLY THE RADIO GODS HAD SPOKEN (TRGHS).  

Sure, the cabinet looked a bit rough, but I had high hopes for this receiver.  A while back I had -- in a similar fit of nostalgia -- bought what had been advertised as a Lafayette HA-600A on e-bay.  But it turned out to be a Lafayette HA-600 (no A).  I immediately noticed a big difference in performance.  That was NOT the radio that I remembered, not the receiver that had carried HCJB and Radio Moscow to me. Joe was clearly offering the A model.  

A few days later I was in Joe's front yard for the hand-off, and a few days after that the HA-600A was on my bench.  

I quickly realized how little I knew about this receiver.  Mine was a Christmas gift, probably in 1973. (A few days ago I talked to my mom and thanked her for driving all the way to New Jersey to get this receiver for me.)   I was so taken with this thing that I feared doing something -- anything -- that might mess it up.  I lived in fear, for example, that some sort of freak mid-winter lightning bolt might destroy it.  I covered it with a towel each night lest dust encumber its "jeweled movements." Obviously I was just not inclined to crack open the case and have a look around. So I didn't, and the receiver remained pretty much an appliance for all the time I owned it.  (I eventually sold it on consignment at Electronics 59 in Spring Valley, New York.  The proceeds probably went toward the purchase of a much better Drake 2-B receiver.) 

I downloaded the manual and familiarized myself with the receiver:  It is a single conversion superhet with a 455 kc IF.  It is all solid state with no ICs -- all discrete transistors and diodes. The manual claims it has a mechanical filter.  I kind of hoped for something like a Kokusai mechanical filter,  but it turns out that the filter was really ceramic, not mechanical.  Bummer.  

The thing fired up right away and was inhaling on the correct frequencies.  I noticed immediately that (as Joe had indicated) some of the controls were scratchy.  I also noticed that the ganged band selection switch was intermittent and required some jiggling to get it to work properly.  A few squirts of Deoxit D5 took care of all that. There seemed to be a bit of dirt in the main tuning capacitor, but I think I managed to blow that out using a can of Dust-off.    I was quickly listening to the SW broadcast stations, and to radio amateurs on 75 and 40 meters. 

Out of curiosity, I compared schematics of the HA-600 and the HA-600A.  There was indeed a big difference -- the front end of the 600 lacks a lot of the RFA amplification circuitry of the A model.  That's probably why is seemed so deaf and so different from what I remembered of the A model. 

There is really not a lot to do on this receiver.  I'll get some paint to fix up the top cover.  I may check the alignment.   But this single conversion receiver is so simple that alignment would be quite easy.  In many ways this receiver seems like a solid state analog to the Hammarlund HQ-100, but without the clock, and without the regeneration circuitry.   The dial lacks the exotic station locations (Java!) that make many of the older receivers so much fun.  I guess this is an indication that this receiver was aimed more at amateur radio operators than at shortwave listeners ( I was both).  I wonder how the ham band-only HA-800 compares to the HA-600A? 

I could pair this receiver up with a DX-40 transmitter that I have on the shelf and I'd be most of the way toward re-creating my novice station.  Anyone have a Globe VFO Deluxe?   That would complete the setup.  

Thanks very much to shortwave listener Joe Pechie for providing what is, for me, a very meaningful piece of gear. 

Here's a short video on the receiver: 

Sunday, September 27, 2020

A Suitcase Portable 40 Meter CW Station from 1951


Wow.  Check this out:

A very nice  rig built by an amazing homebrewer 

And thanks to Al Klase N3FRQ for putting that wonderful web site together. 

Thursday, September 24, 2020

Global Specialties Corporation 6000 Frequency Counter -- Anyone have a Plessey SP8630B Chip?

Continuing my effort to improve my workbench and its test gear, this week I turned to an old frequency counter that I picked up at the Kempton Park Radio Rally in London many years ago. It was not working when I got it, but long-time SolderSmoke listeners will recall the tale of woe that resulted from my having soldered a replacement IC (that Tony Fishpool G4WIF had sent me) UPSIDE down.  Tough times my friends,  tough times. 

Well,  I'm working on it again.  First I converted it from 220 to 110 power.  I had a transformer in the junk box that fit nicely, both electrically and mechanically.  In the course of doing this, I learned something about this counter that I did not know:   As long as it is plugged in, even if you turn it off, the time-base oscillator keeps running.  And get this Color Burst Liberation Army members:  The oscillator runs at 3.579545 MHz.  TRGHS.    

With sunspots scarce and with Pete pessimistic about the solar cycle, VHF and UHF now seem more interesting.  I need to have more test gear for the higher frequencies.  This counter works up to 650 MHz.  Yea! 

When I first fixed this thing, I was quite pleased to get it going with "Input A -- 5 Hz to 100 MHz."  But now I want to get "Input B -- 40 MHz to 650 MHz" working also. I used a 50 MHz signal from my newly repaired HP-8640B to trouble shoot Input B.  I think one of the divider chips is bad.  It is a Plessey SP 8630B.   Does anyone have one of these chips in their junk box?  

Wednesday, September 23, 2020

Wisdom from AA0ZZ: NO LIBRARIES! ASSEMBLER CODE ONLY! -- "Digital Crap" -- "No Magic Fruit" What qualifies as a real rig? Si570 vs. Si5351



Why do you guys make your Soldersmoke podcasts so darn intriguing such that I can’t listen to them in the background while I’m doing something else?   Good grief!  I start listening and before long you make me stop and chase down a rabbit hole to find something new that you mentioned that I had no clue was out there.    Before long I’m doodling out a new sketch or playing with at a new design for something I really need to experiment with or build “next” or something I need to  try.   It is taking too much of my time!!  J

 I’ve been listening to your podcasts for years.   Way back, before I knew you and before I knew you were doing these Soldersmoke blogs with Mike, KL7R, and just before he was so tragically killed, I was collaborating with him on a simple frequency counter project using a PIC microcontroller.  We were making good progress on a neat design.  I later completed the project but always kept his contributions noted as part of the source code. 

 I’ve been making PIC-based VFOs for years – dating back to about 2000 – aiming them at builders who were looking for something to go along with Rick Campbell’s (KK7B) receivers.  Rick is a good friend now, after we met in the Kanga booth at Dayton where we both were demonstrating our stuff.  (Bill Kelsey (N8ET) of Kanga, was the “marketer” for my kits as well as Rick’s for many years.)   My original VFO kits used a DDS (high-end AD9854) that simultaneously  produced I and Q signals which made it perfect for Rick’s phasing gear.  Rick is a big supporter of my work but he still kids me about polluting his beautiful analog world with my “digital crap” (copyright KK7B term).   When I came out with a newer version VFO using a Silicon Labs Si570 PPLL  (I can hear already Pete Juliano groaning) it was a big improvement over the AD9854 in noise/spur reduction.  I documented this all in a QEX article in about 2011 and Rick (and Wes Hayward) were very supportive/appreciative of my work.   

 I have used the Si5351 also and I understand Pete’s point of view.  It’s “plenty good” for most amateur projects.  However, it remains a fact that the Si570 is a better part and produces a cleaner signal.  That’s the reason why the Elecraft KX3 uses a Si570.   Granted, the newer Elecraft KX2 uses a Si5351 but it’s most likely because they wanted to preserve battery life (the Si570 uses more power but not nearly as much as the AD9854) and also to reduce the cost.   I do understand!   I also fully understand the ability of the Si5351 to produce I and Q signals via different channels.  I’ve had extensive conversations about this with Hans Summers, at Dayton and online.  I use a pair of Flip-Flops on the output of the Si570 instead.  My PIC code driving the Si570 is ALL written in ASSEMBLER code.  Yep!   I’m an EE but have had a career mainly in software development and much of it was writing assembler code.   I dare say there aren’t too many gluttons for punishment that do it this way.  I do it because I want to understand every line of code don’t want to be dependent on anyone else’s libraries.  Every line of code in my VFO’s and Signal Generators is MINE so I know I can debug it and it can’t get changed out from under me.   (This problem bit Ashar Farhan hard on the Raduino of his BitX.   Tuning clicks appeared because the Si5351 libraries he used changed between the time he tested it and released it.   I was really appalled when I dug into this and resolved to NEVER use libraries that I didn’t write myself.  Similarly, this also makes me have some distaste for Arduino sketches.  I would rather see ALL of the code including the initialization code, the serial routines, etc, rather than having them hidden and get pulled in from Arduino libraries.  That’s similar to the reason why Hans Summers didn’t use an Arduino in his QCX.  He used the same Atmel microprocessor but developed/debugged it as “C” code with the full Atmel IDE/debugger.                                                                                                            

By the way, Pete  mentioned the Phaser FT8 transceiver by Dave, K1SWL, in a recent podcast.  Dave is a very close friend, even though I haven’t met him in person since about 2000.  We Email at least daily and some of it is even about radio. J   I did the PIC code for the tiny PIC that controls the Si5351 in the Phaser.   Yes, it’s written entirely in Assembler again!   I do know how to do it for a Si5351.  That Si5351 code is not nearly as much “fun”, though.  I know, this will make very little difference to guys who write Arduino “C” code to control it but under the covers it’s a world of difference.   It takes me about 15 serial, sequential, math operations to generate the parameters for the Si5351.  None of them can be table driven and they all have to be performed sequentially.   (This is all hidden in about 5 lines of complex, Arduino “C” code but the operations are all there in the compiled assembler code.)   In contrast, my Si570 code is almost all table driven.   I just have to do one large (48-bit) division operation at the end to generate the parameters.    Yes, that’s a bit of trickery to do in ASM.   There are no libraries do this.

 I will point out one more advantage of the Si570 in comparison to the Si5351.  It has the ability to self-calibrate via software instead of relying on an external frequency standard.  In my Si570 app I can read up the exact parameters for the crystal embedded inside the Si570, run my frequency-generating algorithm “backwards” and determine the exact crystal frequency (within tolerances, of course) for that particular Si570.  Then I update all the internal tables using that crystal frequency and from then on all generated frequencies are “exact”.   I love this!  Frequency often moves by about 6 kHz on 40M.

 Oh yes, I must mention the difference of home solderability of the si570 vs the Si5351.  Those little Si5351 buggers are terribly difficult to solder at home while the Si570 is a breeze.   I know, many folks will just buy the AdaFruit Si5351 board and it’s already soldered on but, again, I like to do it all myself.   No “magic Fruit” for me.

 Now that I retired a couple of years ago and am getting out of the VFO kitting business I can finally build complete rigs instead of just making the next-generation VFO’s for everyone else to use.   I recently build a tiny, Direct Conversion rig with a Si570 signal generator (of course) and a diode ring mixer (ADE-1).  Look at my web page,  to see it, along with my VFO projects that I’ve been building in the past.   As you well know, Direct Conversion is fun to build and the sound is astounding; however, they are rather a pain to use!  Yes, I did make it qualify as a real rig by making several contacts all over the country.  (Wes Hayward gave me the criteria:  he told me that I must put any new rig on the air and make at least one contact before it qualifies as a real rig.)  

 The new rig that’s on my workbench is my own version of a phasing rig, experimenting with a Quadrature Sampling Detector (QSD, sometimes called a “Tayloe” mixer), using some ideas from Rick’s R2 and R2Pro receivers and many innovations of my own.  At present my new higher-end Signal Generator works great, the QSD receiver works great (extremely quiet and MDS of -130 dB on 40 meters) and the transmitter is putting out about 16 watts with two RD16HHF1’s in push-pull.  You can take away my “QRP-Only-Forever” badge too, not that I’ve ever subscribed to that concept!  Still more tweaking to do with the TX but now I’m also working on the “glue” circuitry and the T/R switch.   The SigGen, RX and TX are all on separate boards that plug into a base board which has the interconnections between boards and the jacks on the back.  I’ve built DOZENS of variations of each of these boards. Fortunately they all fall within the size limit criteria to get them from China at the incredible price of $5 for 10 boards (plus $18 shipping) with about 1 week turnaround.   Cost isn’t really an object at this point but it’s more of getting a hardware education that I sadly missed while I concentrated on software for so many years.  it’s certainly nice to have willing mentors such as Rick, Wes, Dave (K1SWL), Don (W6JL) and many others to bounce my crazy ideas off.  Yes, I’m having a ball!  

 I was licensed in 1964 but out of radio completely from 1975 to 1995.   Do you like the picture of my DX-100 on my web page?  My buddy in the 60’s had a Drake 2B and I drooled over it but couldn’t afford one.

Now I must finish this rig before you guys send me down another rabbit hole.   Too many fascinating things to think about!   I literally have a “priority list” on the my computer’s desktop screen.  Every time I come up with a new project idea – something I really want to play with such as a Raspberry Pi, SDR, etc, I pull out the priority list and decide where it fits and what I want to slide down to accommodate it.  That’s my reality check!

 Take care, Bill.   Thanks for taking the time to give us many inspiring thoughts and ideas.


-Craig, AA0ZZ

Monday, September 21, 2020

HP8640B Internal Frequency Counter Fixed (More Repairs Pending)


The HP8640B is a complicated machine.  Above you see just one sub-assembly, and the page from the manual that describes it.  This is what I've been working on.  The little spring "tine" fell out of one of those discs behind the two control knobs.  So I had to open this thing up, find the spot from which the tine had fallen, and glue it back in.   

I used Gorilla Super Glue, followed 24 hours later by a dab of JB Weld "minute weld" dual epoxy. One of the other tines was about to fall out, so I went ahead and gave all the tines in this assembly the glue treatment.  ( I bought some "Weld On" acrylic cement but the warnings on the label were quite sobering.  So I left that can sealed up.) 

This morning I put the thing back together.  This is not easy.  At one point a spring popped and a tiny metal part that is probably irreplaceable seemed to fly away into the black hole that is the shack's carpet.   I had just about given up hope when I found the thing sitting right in front of me on the bench.  TRGHS. 

The HP8640B fired up right away without trouble and the internal frequency counter is working fine. 

As I noted in the last SolderSmoke podcast, a very nice community devoted to the HP8640B has developed around the world.  Here are some of the notable participants: 

Bill at Electronics Revisited is a very nice fellow with lots of experience on the HP8640B.  He offered to sell me a replacement unit for the assembly pictured above.  If you have an ailing HP8640B and are looking for someone to work on it for you, Bill is the guy you should talk to:  He also very kindly offers to answer any questions you may have about the HP8640B. 

Here is the e-bay page of the fellow in Bangalore who makes the brass gears.  Mine are on the way! 

Marcus VE7CA has a great site devoted to the HP8640B:

BH1RBG in China has a nice site describing his adventures with the HP8640B:

K6JCA has a good blog post about fixing the tines and the gears: 

Steve Silverman (who gave me this HP8640B) found a really useful  history of the device: 

And of course special thanks to Dave VE3EAC who alerted me to the falling tine problem and put me on the path to a successful repair.  

The gears should be here in a few weeks, so that will be another opportunity to work on this HP8640B.  Also there are some tines in the attenuator assemby that might reinforce with the glue treatment. 

Saturday, September 19, 2020

SolderSmoke Podcast #225: Mars, uSDX, G-QRP, HP8640B, DX-390, Rotary Tools, Walla Walla SDR, MAILBAG

SolderSmoke Podcast #225 is available

Mars,  West Coast smoke.

Pete's Activities: 
-- DC receivers.
-- CW offset
-- GQRP talk
-- The uSDX project

Bill's Bench
-- Sliding into the Vintage Test Gear Cult:  HP8640B . 
-- Fixing up and figuring out Radio Shack DX-390 receivers.  
-- 220 to 110 on a few remaining devices.     
-- Got myself a Dremel-like rotary device.  

Tech News: 
-- ARRL/TAPR Convention:  SDR project from Walla Walla University students.   Intuitive explanation for why desired and image freqs in a mixer come out with very useful phase differences.  

-- Chuck Adams' Amazing Lab Notebook.   Includes a simple circuit to measure resistance and Q in crystals.  FB. 


-- Dino KL0S  SITSing in his shack, homebrewing 9 MHz filters  FB Dino.  Airborne! 
-- Dave NT1U sent us the famous 1968 QST Article by W7ZOI re DC RX.  
-- Ron K0EIA listening to SWBC staions with uBITX.  
-- Ted AJ8T  Korguntubes making a 12AX7 equivalent.  
-- Joel N6ALT sent me a nice DX-390 manual.  Thanks Joel
-- Bob KD8CGH alerted us to the uSDX project -- story on the blog. 
-- Craig AA0ZZ Sent a great message with insights on computer code -- I will put up on the blog. 
--Tracy KN4FHX reports on optimistic prognosis for SolarCycle 25.  Some chickens may have to be sacrificed.   
-- Stephen M0OMO Thanks SolderSmoke for rekindling interest in this hobby. 
-- Paul VK3HN  has a cool new rig -- The Prowler -- check it out
-- Steve N8NM working on his Sunbeam car -- Pete already knew about the carburetor synch problem.  N6QW knows everything. 

Friday, September 18, 2020

Mixer Insights using Propellers and Cameras -- From Walla Walla University. And SDR Design Info.

Pete Eaton sent us this video from the 2020 ARRL/TAPR Communications Conference.   I have the portion of interest cued up (above).  (The portion of interest begins at 6:59:46.)

There is a lot of really cool SDR design info in this video and in the associated paper  (the TAPR site says you have to pay the ARRL $9 for the paper, but in the comments someone says the papers will be available free after the conference).  

What caught my attention was the students' discussion of mixer action.   They use an analogy with a spinning propeller (the incoming RF) and a camera (triggered by the local oscillator) that samples the incoming signal at a specific rate. This is analogous to a Quadrature Sampling Detector. 

The really interesting part for me was how this analogy allows us to see how phase differences between the desired signal and the image signal arise.   These phase differences permit an SDR receiver (or indeed an old fashioned phasing Direct Conversion receiver) to reject the image while allowing the desired signal to pass.  

This is a key point in understanding mixers, and is really quite amazing. Before I saw this video, I had just come to accept (without understanding WHY) that the desired signal and the image signal would have phase differences, EVEN IF THEY WERE COMING OUT OF THE MIXER AT THE SAME FREQUENCY.  It is this phase difference that allows us to knock one down while allowing the other to pass. The propellers and cameras of Walla Walla University gave me insight as to how and why these phase differences exist.  

In their paper, the Walla Wall group mention uSDX, the project that is currently generating so much excitement around the world: 

Low-cost is not the only reason SDRs have become more popular among the amateur radio
community. More recently, Guido Ten Dolle’s μSDX open source transceiver has generated
increasing interest in quadrature sampling down-conversion SDRs in the homebrew QRP
community. Guido, PE1NNZ, was able to modify the QCX, QRP transceiver for SSB operation
with an efficient class-E amplifier, using only an ATMEGA328 and Arduino code to run the QSD
SDR. This groundbreaking work in this type of SDR has inspired various renditions of Guido’s
radio, fostering a lively group that can be followed at

Kudos to Caleb Froelich, Dr. Rob Frohne KL7NA,  Konrad McClure, Joshua Silver, and 
Jordyn Watkins KN6FFS,  all of Walla Walla University,  for some really impressive work.  (BTW:  Rob tells me that back in the mid-90s he too built one of Rick Campbell's phasing receivers and wrote a QST article about it  (probably the first SDR article published by QST).  Details on the project are here:

Monday, September 14, 2020

A Regen Receiver Made with Homebrew Tubes

Wow, a regen receiver using homebrew triodes.  Makes me feel like such a pathetic appliance operator, what with all my STORE-BOUGHT TUBES... I hang my head in shame.  Real hams make their own tubes.  And vacuums, apparently.  

Here is how the tubes were made: 

Lots of amazing videos in this YouTube channel: 

Kudos to jdflyback!  (Who is this amazing homebrewer?) 

Sunday, September 13, 2020

HP8640B -- Fault Found! A very TINY and Hard-to-Fix Fault


I've been troubleshooting the internal counter in my HP8640B signal generator. The generator itself works fine.  And the counter works fine for all signals coming in on its "external" port.  But the internal counter stopped working properly above 16 MHz. So I started digging into the manuals and the schematics, re-familiarizing myself with the digital logic behind pre-microcontroller  frequency counters.  NOTE:  If you are working on one of these, be sure to be using the correct version of the manual and schematic. At one point I found a really nice high def copy of an HP8640B manual (for one used in a Patriot Missile System!) only to discover that MY A8A3 board was significantly different from the one in this manual.  BAMA provided a manual that matched my device:

Every dark cloud has a silver lining.   Here, the silver for me came from opening up the HP8640B.  What an impressive looking piece of gear.  It looks like something from the Apollo command module, or perhaps from a nuclear weapon.  "The RF source is a 256 to 512 MHz cavity-tuned oscillator that is mechanically tuned..."  There is phase lock circuitry.  The are AM and FM modulators and a really useful array of attenuators.  There is a frequency counter with an external port and an internal frequency counter that measures the original 256-512 MHz signal, then divides down to give a very accurate readout of the output frequency.    This is the kind of device that would generate a cult following.  Count me in! 

Also,  I've sometimes lamented the lack of VHF test gear on my work bench -- the HP8640B could really help me move me into the VHF range.

I started the troubleshooting with some observations and noodling. At what frequency did the internal counter stop working?  What did the readout look like when it stopped working?  What device failure could lead to these symptoms?  I was aided in this by suggestions sent in by readers of my previous blog posts.  Thanks guys.  

I was just getting ready to start some intrusive testing on the logic devices in the internal counter when Dave VE3EAC sent me this: 

I think you might be overthinking the failure mode here. I had a similar problem with my unit and it was one of my early Covid-fix-it projects. There is an assembly that controls the bands on the front. It has the famous gears that crack. On the back side are two sets of rotary switches that control a lot of stuff. The switches are of a very unique HP design and offer a lot of advantages over traditional switches EXCEPT they fail in an unusual manner. A PC board has all of the interesting wiring and very tiny double leaf springs short tracks together as needed. The springs tend to break away from the plastic posts on the rotating plate and not make the needed contact. Very carefully examine the insides of the 8640 and your bench top to see if any have fallen out. These are difficult to buy or fabricate. The disk is designed to be rotated 180 and use a new set of posts to locate the springs. Use a small dab of epoxy to set in place. The totally mechanical repair fixed my unit that also would not read above 16 MHz. There are a number of web pages that give great detail of this repair. Also it is worth while to replace the Delrin gears if they are cracked. Replacement brass ones are available on eBay and they will permanently fix the gear problem.

I had thought about the problem being in the frequency range switch, but I had sort of tested for this by slowly rocking the switch through various positions as I watched the display.  A dirty rotary switch will usually allow the circuit to intermittently work as you rock the switch.  But this didn't happen.  And the HP switch felt quite sturdy, so I focused on the circuitry.  

When I got VE3EAC's message, I carefully flipped the HP8640B over and for the first time opened the bottom of the compartment.  The bottom view is much more impressive than the top view: 

The switches that VE3EAC wrote about  are just below the ribbon cable near the center front. I could see the little springs that he was discussing on the switches.  They appear MUCH more delicate than the rotator on a standard rotary switch.  And I didn't see any of them lying around below the switch.  But when I tried to flip the HP8640B over, something in there moved and caught my eye.  I pulled out some tweezers and pulled this out: 

Wow.  That little spring contact fell off the switch.  That was preventing the HP8640B internal counter's time base from changing as I went above 16 MHz.   It is ironic that such a big and solidly built device such as the HP8640B should be laid low by such a TINY part.  

This gets me back to my original question:  Discretion or valor?  Getting that spring back onto that switch will not be easy.  VE3EAC sent me this K6JCA link describing how to do this.  Yikes, it even requires the purchase of a special tool!  

I'm going to let the HP8640B sit there with the cover off for a while.  It will be taunting me, challenging me to fix it, to make it work the way Hewlett and Packard intended.  It may take a while, but I think I'm going to have to accept this challenge. I've become  real fan of the HP8640B and it would be a shame to leave it wounded like this. 

Friday, September 11, 2020

HP8640B Counter Repair --- Discretion? Or Valor?


Inspired by BH1RBG, I cracked open the HP8640B to have a look at the counter circuitry.  Above is the view that greeted me.  That is the main counter board after I pulled it out of its socket.  You can see the seven little red LED display modules.  

It is not as bad as it looks.  In fact, I found the construction and accessibility of the HP8640B to be quite impressive (much better than the Tek 465 with all its flaky plug-in transistors). The manual has good, detailed info on how to get into the various compartments, and even as you work, instructions on which screws to remove or loosen appear on the tops of each RF-tight compartment. Nice. This thing was obviously built with the needs of a future repairman in mind. 

Above is that same board flipped over.  Again, not as bad as it looks. 

Above is board A8A3, the board that I suspect is causing me trouble.  When I go through the troubleshooting routines in the manual, I get to the point where they check decimal point position.  Everything is fine UNTIL I GET TO 16 MHZ.  Then the decimal point is not where it should be and the frequency displayed is very wrong.  (This is in the internal mode -- the counter works fine with an external signal source).  The manual then sends me to Service Sheet 15 which points to possible problems on this A8A3 board, U3, U7 or U6D. 

Troubleshooting this will be tough.  I do not have the extender board that would allow me to test this A8A3 board with the other counter board raised up above it and operating.  BH1RBG noted that getting the extender boards is almost as tough as getting the HP8640B itself. 

While it really bugs me (!) to have  a part of this device not working properly,  I could just leave it as is.  The signal generator is working fine, and I could use the external counter input to check the frequency.  But this is a real kludge. 

What do you folks think?   Fix it or leave well enough alone?  Discretion or valor?  Anyone have an extender board?  Any ideas on where the fault might be?    

Thursday, September 10, 2020

The Agony of Troubleshooting -- From China


I am troubleshooting my beloved NYC HP8640B Signal Generator (thanks to Steve Silverman and Dave Bamford).  Some of you may wonder why I don't just replace this beast with something small, lighter, cheaper and newer.  Well, I have not found any new sig generators that will do what this beast does:   It goes all the way up to 256 MHz (higher with an extension kit).  It has a great attenuator in it so you can set the output just where you want it.  AM or FM modulation.  Really useful.  So I think I'll fix it. 

My problem is that the internal freq counter stops working above 16 MHz. Using the very extensive  documentation, and without even really opening up the machine, I think I have located the fault.  I think it is in the Counter Time Base Assembly board A8A3.   Now of course, the fun begins.  (Tips, advice, solutions, and words of encouragement would all be appreciated.) 

While planning my assault on A8A3, I came across the web site of BH1RBG.  He too has recently been working on an HP8640B.  His problem was different, but when I read through his site I saw evidence that the agony of troubleshooting is something that is the same all around the world.  Check out his description of the agony: 

I even suspected the LM723 should had something bootstrapping circuit, make sure the Q4 sure start. Because the external reference VR3 is floating too, oh, my godness.

I became hopeless, and ordered several LM732,and waiting delivery for days. This beast frustrate me so deeply, changed the LM723 does not help anything. And i almost desoldering everything in the board!

Oh man, I've been there. Several times while in the throes of a troubleshooting battle I have actually had dreams of removing all the parts from a troublesome PC board.

BH1RBG has a very interesting site with lots of ham radio projects:

Wednesday, September 9, 2020

Dalibor Farny: Making Nixie Tubes in a Castle in the Czech Republic

“Our customers are interested in technology – some people buy paintings for their wall; our customers buy a technical piece of art. I think they appreciate the fact that someone is keeping old technology alive and they want to support us."

Dalibor Farny is manufacturing Nixie tubes and devices that use them.  He is working out of a castle in the Czech Republic.  Above is a video about his renovation of his workshop.  It was nice that he involved his kids in the project. 

This article tells his story:

Here is his website:

YouTube Channel:

Tuesday, September 8, 2020

Builds Oscilloscope at age 12! Nick has THE KNACK

Thanks to Grayson Evans for sending us this very encouraging video.  
It is from Tektronix;  I wonder if Alan W2AEW provided some ideas and inspiration? 

More stories like this:  

Sunday, September 6, 2020

Twenty-nine S-38s on Craig's List

This is almost like a nightmare.  I guess it could be worse -- they could all be E models.

Thanks to Jim W3BH for alerting us to this, uh, opportunity. 

Marc Verdiell Has The Knack

Here is Marc Verdiell, the "Curious Marc" who repaired the Soyuz Clock (shown in yesterday's blog post).  

Really cool.  Many SolderSmoke fans will completely understand Marc and his passion for 

Saturday, September 5, 2020

Taming Glitches in a Soyuz Space Clock (Plus -- Inside a Logic Chip and How Crystals Work)

Thanks to Bob KD4EBM for sending this.  

There is so much good info in this video:  They crack open a logic chip and look at the internal construction (it is entirely understandable by mortal minds).  They use cool test gear to troubleshoot the clock from a Soyuz spacecraft.  They explain very clearly the series and parallel resonances of quartz crystals, then display these resonances on a very nice spectrum analyzer.

The creator of the video is CuriousMarc.  He has many other interesting projects: 

His bio is here: 

One paragraph from his bio really resonated with me: 

Working on this old stuff forces me to deal with the very fundamentals of electronics (and electro-mechanics). The principles are exactly the same as today, but nothing is hidden in mysterious circuits - you can understand and fix everything. Years of Moore's law has sure given us gobs of transistors, oceans of memory and a glut of gigacycles, but many times, particularly in consumer hardware, these are simply used to cover up poor and inefficient designs - and resource devouring software. What Intel giveth, Microsoft taketh away, as they say. It often irritates me that my PC takes several seconds to react to a simple command, in which time it must have executed billions of unnecessary instructions and consumed a few gigabytes of memory, no one knowing exactly what for anymore. Nothing like this in old high-end hardware: designs are pure and efficient, and the lack of resources is compensated by engineering mastery and immense cleverness, which is a joy to reverse engineer. Not only does it teach us timeless electrical fundamentals and engineering tricks, but it also gives us a much better appreciation of today's tech. How did all the technology we take for granted came to be? It will make you a far better engineer and inventor if you take the time to be a thorough student of the inventions of your illustrious predecessors.

Monday, August 31, 2020

Global Collaboration: The uSDX -- A Multi-Mode QCX

There is a new open source, home brew, multi band, multi mode QRP transceiver that grew out of the QRP Labs QCX. Through some serious magic it retains an efficient class E RF amplifier for sideband and digital modes. It crams impressive SDR capabilities into an Arduino. More info at

The basic work appears to have been accomplished by Guido Ten Dolle PE1NNZ. It uses pulse width modulation of the PA supply voltage to transmit  modes other than CW while retaining class E efficiency and uses a direct conversion SDR receiver.
There are several variants by different developers. I built a variant designed by Barbaros Asuroglu WB2CBA that uses through hole components (mostly) and I'm pleased with it's performance. I also designed and 3D printed a case.

This has an interesting development process with contributions by many, including the usual gang of suspects: Hans Summers, Ashhar Farhan, Manuel DL2MAN, Kees K2BCQ, Allison KB1GMX and Miguel Angelo Bartie PY2OHH. I apologize to the many others whose names I didn't list.

The band switch multiband version by DL2MAN is even smaller, but with SMD components which I wasn't ready to tackle yet.

BTW - your podcast encouraged me to go in this direction. I built a BITX 40, a uBITX (sent you a pix of it in an old Heathkit Twoer case), U3S, QCX and now my first step from kits to built from plans.

Bob   KD8CGH

Sunday, August 30, 2020

Music Video -- "The Spirit of Radio" by Rush

Thanks to Thomas from The SWLing Post for putting this on his blog.

Friday, August 28, 2020

Andreas Spiess (The Guy with Swiss Accent) -- Workshop Tips

Thanks to Paul Taylor VK3HN for alerting me to the YouTube channel of Andreas Spiess.  There are lots of great projects there, including several videos on building an Oscar 100 ground station.  

In the video above, Andreas talks about his lab/workshop.  He is more focused on digital projects than I am, but I found many of his tips applicable to the analog world. And of course the more digitally oriented readers will find Andreas's observations especially useful. 

I was sold on this video when Andreas reached to his book shelf and showed us Tracey Kidder's "Soul of the New Machine."   That is the book that brought the word "soul" into the SolderSmoke lexicon. 

There are many great videos on Andreas's channel.  I found his Playlists page to be a good way to see the many different catergories of his projects:

Thanks Andreas. 
Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column