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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: https://nvhrbiblio.nl/schema/Lafayette_HA600A.pdf )

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:   http://marc.retronik.fr/AmateurRadio/SSB/Single-Sideband_Detectors_%5BHAM-Radio_1968_8p%5D.pdf      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.   

https://soldersmoke.blogspot.com/search?q=Basta

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: 

https://www.npr.org/2020/10/04/920038792/mafalda-cartoonist-quino-dies-at-88

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.  

https://miscdotgeek.com/bitx40-rebuild-part-1-mistakes-planning-and-teardown/

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: 

http://bitxhacks.blogspot.com/


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

GM4OOU






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:

http://www.skywaves.ar88.net/homebrew/W9FKC.pdf

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?  


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