Putting the "Mate for the Mighty Midget" Back to Work -- With a DX-100 on 40 Meter AM

After working on it for a while I got so fond of my old Hammarlund HQ-100 that I moved it from the AM/Boatanchors operating position over to a more convenient spot right next to my computer.  This left a big gap on the receive side of the AM station.  

I briefly put my HRO-ish solid state receiver above the DX-100, but I'm afraid that receiver needs some work.  More on that in due course. 

I thought about putting my SOLID STATE Lafayette HA-600A atop the thermatronic DX-100, but this just didn't seem right. The Radio Gods would NOT approve. 

So I turned my attention to the Mate for the Mighty Midget that I built in 1998 and have been poking at and "improving" ever since. 

This receiver worked, but not quite right. It received SSB stations well enough, but when I turned off the BFO I could no longer hear the band noise. I wasn't sure how well the RF amp's grid and plate tuned circuits tracked.  And I had serious doubts about the detector circuit that Lew McCoy put in there when he designed this thing back in 1966. 

As I started this latest round of MMMRX poking, I realized that I now have test gear that I didn't have in 1998:  I now have a decent oscilloscope.  I have an HP-8640B signal generator (thanks Steve Silverman and Dave Bamford).  I have an AADE LC meter. And I've learned a lot about building rigs. 

FRONT END TRACKING

The MMRX has a tuned circuit in the grid of the RF amplifier, and another in the plate circuit of the RF amplifier.  There is a ganged capacitor that tunes them both.  They need to cover both 80/75 and 40 meters. And they need to "track" fairly well:  over the fairly broad range of 3.5 to 7.3 MHz they both need to be resonant at the same frequency.  

McCoy's article just called for "ten turns on a pill bottle" for the coils in these parallel LC circuits.  The link coils were 5 turns.  No data on inductance was given.  Armed now with an LC meter, I pulled these coils off the chassis and measured the inductances of the coils.  I just needed to make sure they were close in value.  They were: 

L1 was .858uH L2 was 2.709         L3 was .930uH  L4 was 2.672

Next I checked the ganged variable capacitors.  At first I found that one cap had a lot more capacitance than they other.  How could that be?  Then I remembered that I had installed trimmer caps across each of the ganged capacitors. Adjusting these trimmers (and leaving the caps connected to the grid of V1a and V2A, I adjusted the trimmers to get the caps close in value.  I think I ended up with them fairly close: 

C1: 63.77-532 pF          C2 64.81 -- 525.1 pF

I put the coils back in and checked the tracking on 40 and on 80/75.  While not perfect, it was close enough to stop messing with it.  

DETECTOR CIRCUIT

I've had my doubts about the detector circuit that Lew McCoy had in the MMMRX.  In his 1966 QST article he claimed that the circuit he used was a voltage doubler, and that this would boost signal strength.  But I built the thing in LT Spice and didn't notice any doubling.  And consider the capacitors he had at the input and output of the detector:  100 pF.  At 455 kHz 100 pF is about 3500 ohms.  At audio (1 kHz) it is 1.5 MILLION ohms. Ouch.  No wonder years ago I put a .1 uF cap across that output cap just to get the receiver working. 

Scott WA9WFA told me that by the time the MMMRX appeared in the 1969 ARRL handbook, the second "voltage doubling" diode was gone, as were the 100 pF caps.  Now it was just a diode, a .01 uF cap and a 470,000 ohm resistor.  I switched to the 1969 Handbook circuit (but I have not yet changed the 1 meg grid resister to 470k -- I don't think this will make much difference).  Foiled again by a faulty QST article, again by one of the League's luminaries. 

6U8s out, 6EA8s in 

We learned that the 6U8 tubes originally called for by Lew McCoy are getting old and not aging well.  So I switched all three to more youthful 6EA8s.  This seemed to perk the receiver up a bit. 

MUTING from the DX-100

My K2ZA DX-100 has a T/R relay mounted in a box on the back of the transmitter.  When the Plate switch goes up, it switches the antenna from receiver to transmitter.  The box also has a one pole double throw switch available for receiver muting.  I put the common connection to ground, the normally connected (receive position) connect the ground terminal of the AF output transformer to ground -- it is disconnected from ground on transmit.  The other connection (normally open) is connected to the antenna jack -- on transmit this connection ground the receiver RF input connection.  These two steps mutes the receiver very nicely. 

Replacing Reduction Drive

Over the years I have had several different reduction drives on the main tuning cap.  I had a kind of wonky Jackson brothers drive on there that needed to be replaced.  I put in a new one -- this smoothed out he tuning considerably. 

Ceramic Resonator

I never could get McCoy's 455 kc two crystal filter to work right.  So at first I made due with the two 455 kc IF cans.  This made for a very broad passband.  Then I put a CM filter in there.  This was more narrow, but with a lot of loss.  There may have been others.  But the filter spot is currently held by a 6 kHz wide ceramic filter.  This one is my favorite so far. 

Digital Readout

When I was running the DX-100 with the Hammarlund HQ-100 I built a little frequency readout box.  The box was from a Heath QF-1 Q multiplier (I am sorry about this).  The readouts are in Juliano Blue and come via e-bay from San Jian.  I now have it hooked up to the DX-100's oscillator.  I haven't tapped into the MMMRX's oscillator yet. 

McCoy SSB Crystal Filters (1963) -- But Apparently NOT the Real (Lew) McCoy

 

Last month we were talking about this company.  Someone thought it was run by Lew McCoy of ARRL Homebrew fame, but it now appears that our Lew McCoy was not involved in the company. 

Note how they provide TWO carrier oscillator/BFO crystals for each 9 MHz filter, one for USB, the other for LSB. 

They were pricey too:  In 2021 dollars, that Golden Guardian would cost $390. 

Thanks to the K9YA Telegraph for posting the ad. 

KG7TR's Magnificent 75S-2B Receiver -- Tubes, an Si5351, an Arduino, a Bit of Collins, and a Bit of a Drake 2-B

 

Oh man, I share this with much trepidation because the last time I posted something about the work of Mike KG7TR,  Pete N6QW said he felt like putting all of his own work in the dumpster, so much better was the artistry of KG7TR.  This receiver is so cool and so well-done that we now  might have to post a guard outside the N6QW shack -- heck Mike even has an Arduino Uno and an Si5351 in there!  Don't do it Pete!

I was led to this magnificent receiver by the very humble 6U8 tube.  Scott  WA9WFA and I have been learning (mostly from Grayson KJ7UM) that the much used and sometimes loved 6U8s (three of them in our "Mates for the Mighty Midget")  might be a bit long in the tooth, old even by Thermatron standards.  I was worried when I remembered that my Drake 2-B has a 6U8 in it -- V2, the first mixer.   So I Googled for more info and was led to this amazing receiver, a 2018 creation by KG7TR.  How did we NOT see this for almost four years?

Here is more info and pictures: 

http://www.kg7tr.com/75s-2b-receiver.html

Here is Mike's write-up of the project: 

http://nebula.wsimg.com/c2281e9bdf3b54da42ca4b0b541b4ec9?AccessKeyId=D18ED10DA019A4588B7B&disposition=0&alloworigin=1

Mike KG7TR's web site:

http://www.kg7tr.com/ 

As for the 6U8s, well Grayson says the tube has been getting something of a bum rap.  And  KG7TR has two of them in this receiver, so I will obviously have to give the 6U8 another chance.  

--------------------

I didn't know that Lew McCoy had his own crystal and crystal filter company: 

http://www.kg7tr.com/the-real-mccoy.html

Mate for the Mighty Midget with 6 kHz Ceramic Filter

I built this receiver back in 1998, but I continue to have fun tinkering with it. I wrote an article about it for "Electric Radio" magazine (Number 115).   One of the major shortcomings was the crystal filter that Lew McCoy prescribed.  It was very difficult to get 455 kHz crystals to work well as filters.  At various times I've had all kinds of replacements in there in place of Lew's filter:  a 455 kHz IF can, a Toyo CM-5 hybrid ceramic filter, a fancy Millen high Q IF transformer. None of them really worked well. 

Recently I put a little +/- 3 kHz ceramic filter in there.  This is a 6 kHz wide filter at around 455 kHz.  I think it works really well.  Above you can see the receiver in action.  I use it with a little powered computer AF amplified speaker -- I just don't like headphones.  

The latest  filter mod with the 6 kHz ceramic filter  is shown above. 

Above you can see what the whole 455 kHz filter and transformer passband looks like. The input was through a 2k resistor placed between the .001 uF cap and the filter. The output was also through a 2k resistor placed at the top of the secondary of T1. (So don't pay any attention to the insertion loss.) 

The NanoVNA is displaying 2 kHz per division.   I put the BFO at 451 kHz.  This results is excellent opposite sideband rejection.  The filter is really too wide for SSB, but it is about perfect for AM, which I listen to quite often on both 75 and 40.  SSB and AM both sound quite good.  Check out the video above. 

It is kind of amazing what can be done with just three 6U8 tubes. 

There are many previous SolderSmoke blog posts about the Mate for the Mighty Midget Receiver here:

https://soldersmoke.blogspot.com/search?q=Mighty+Midget   Be sure to keep selecting "earlier posts" so see more. 

WA9WFA's Mate for the Mighty Midget 1966 QST Receiver

Scott WA9WFA and I have been exchanging e-mails about his Mate for the Mighty Midget receiver project.  This morning I finally took a look at Scott's we page on this effort.  There was a lot there that resonated.  For example: 

"I remember the moment very clearly.  June 1966 I was sitting in a lawn chair reading a stack of QST's that I had brought along to the summer cabin.  The February 1966 issue the Beginner and Novice section introduced the "Mighty Midget Transmitter", a 10 watt crystal controlled transmitter.  The April 1966 issue Beginner and Novice section introduced the "Mate for the Mighty Midget" which was a three tube super-heterodyne Novice type receiver.  Over the course of that summer I read and re-read those articles a jillion times.  Being 13 years old, I didn't have the electrical or mechanical skills to pull off such a project so I could only dream about it.  In 1970 I bought a handful of the parts.  In 1976 I bought more parts.  In 2021 I decided to build it while I still had the ability to do it.  This project is only my second homebrew radio project so I am still learning things every second of the way...

 

While I am not expecting to much in performance, the 13 year old in me is ever hopeful that this 1966 Novice receiver will be the most wonderful radio ever made.   73, Scott WA9WFA"

Scott's MMM RX page: 

https://www.qsl.net/wa9wfa/MateForTheMightyMidget.htm

Scott and I are now both updating the MMM RX by substituting 455 kHz ceramic filters for Lew McCoy's FT-241 crystal filter.   I have my filter wired in now, and it is working well.  Scott plans on soldering his in today.  I will post on this mod soon. 

On his QRZ.com page, Scott notes the need to fight the temptation to further soup-up this simple receiver:  "I did have to resist the temptation to add another audio stage, a mechanical filter, AGC, 2nd IF amplifer stage, etc..."

Exactly right Scott.  Resist the temptation.   Simplicity is a virtue.  I do use an outboard, powered computer speaker, but I justify this by telling myself that I just don't want to use headphones.  But I could use headphones, so this is OK.  OK?  

Scott's QRZ.com page: 

https://www.qrz.com/db/wa9wfa

I must add that I think the yearning of Scott's inner 13 year-old can be fulfilled by the MMM RX.  I think it is pretty wonderful.  It is -- in my view  -- not as good as a Drake 2-B, but it is FAR better than an S-38E, and it is better than a Lafayette HA-600A (wjm).  

Scott WA9WFA's Mate for the Mighty Midget Receiver is WORKING! (Video)

Wow, Scott got his Mate for the Mighty Midget receiver to work and he is obviously overjoyed with the result.  All of us who have struggled with a homebrew project know just what this feels like.  And it is very cool that Scott got some useful guidance from Charlie Morris in far-off New Zealand.   Congratulations Scott.  I'm really glad you stuck with it.  

Scott's success comes at a good time:  Pete N6QW is building W4IMP's three tube "IMP" SSB transmitter (also from the 1960s).   I accept responsibility for naming Pete's project:  It will be known as "Pete's IMP" or, memorably,  "The PIMP."  For a look at Pete's rig go here: 

http://n6qw.blogspot.com/2021/09/lets-build-something-with-vacuum-tubes_23.html

Scott had problems getting Lew McCoy's 455 kc crystal filter to work.  So did I.  It turns out that this is a very old problem, going back to World War II.  In Don Stoner's 1959 "New Sideband Handbook" on page 54 he writes of homebrew filters in the 400 to 500 kc range:  

"Inexpensive crystal filters constructed from war surplus FT-241 type low frequency crystals are very popular with the 'do it yourself' hams. These CT cut crystals have been plentiful and relatively cheap for a number of years and are in the hands of many Amateurs. The general run of war surplus crystals may or may not be good. Experience has shown that one out of four of these crystals are usually defective in one way or another." 

Stoner was writing just 14 years after the war.  Add another six decades to the age of these crystals -- often decades spent in musty basements -- and you can imagine the percentage of bad 455 kc FT-241  crystals increasing.  So I think Scott is wise to seek an alternative to McCoy's crystal filter. 

Scott's original build of the MMMRX receiver is just so nice.   In the video he says he plans to go back to it after he gets the expanded version fully functional.  He should definitely do that -- his  original version looks so good.  I think it is probably very close to working properly. 

Thanks Scott, and again, congratulations OM. 

Joe Galeski's 1960 "IMP" 3 -Tube Filter SSB Transmitter, and the Spirit of SSB Homebrew

Here is another important bit of SSB history.  In  May 1960, Joe Galeski W4IMP published an article in QST describing his super-simple SSB transmitter.  While Tony Vitale's "Cheap and Easy" rig was a phasing design, Joe came up with a filter rig.  He built USB filter at 5775 kc.  With it, he ran a VXO at around 8525 kc. This put him on 20 meter USB. 

Here is the QST article: http://marc.retronik.fr/AmateurRadio/SSB/A_3_tubes_filter_rig_%28SSB%29_%5BQST_1960_5p%5D.pdf 

In discussing how to put this rig on other bands, Joe got the sideband inversion question exactly right: 

Thank you Joe!  

Joe even provides an comment that seems to capture an important element of the homebrew SSB ethos.  Joe homebrewed his filter, but he mentioned the possibility of using a store-bought filter: 

That's the spirit Joe!  

Along the same lines, Jim Musgrove wrote in Electric Radio: 

Having built Lew McCoy's Mate for the Mighty Midget receiver (which also used just three tubes), I can't help thinking that an IMP-ish transmitter would be an excellent complement to the Mate for the Mighty Midget.  

Jim Musgrove K5BZH knew Joe Galeski and wrote about him in the January 1992 issue of Electric Radio.  Jim wrote that Joe was an optometrist by profession. When OE1FF wanted to know the cost of building an IMP, Joe Galeski boxed up the original and sent it to him.  FB Joe. 

In December 1961 Joe Galeski published a QST article describing a transistorized version of the IMP -- this rig ran on 15 meters.  K5BZH wrote that Joe later published an article about a small, solid-state transceiver,  appropriately called "The Shrimp." 

DONE! Jan's AMAZING Mate for the Mighty Midget Receiver

Hi Bill,

  

Finally the Mate for the Mighty Midget is finished, just in time for the G-QRP Valve Day 12-13^th of November.

Got the LO fixed for 40m by lowering the parallel capacitor from 150 pF to 100 pF.

Also the 68 pF series capacitor was lowered to 33 pF for some more band spread on 40m.

It now receives from about 7.0 to 7.4 MHz and from 3.45 to 4.0 MHz

Had to exchange C1 in the end, the one used initially quit every now and then.

I only had a large 3 section variable in the junk box covering 10-550 pF, which works fine now.
For the lower end of 80m I had to add additional 47 pF next to the 47 pF trimmer caps, so there it is about 600-650 pF max!

At the high end of 40, it is also just not too much.

The meter was used as a position indicator for C1.

Tried several ideas, but with no separate tube for AGC, I couldn’t get it to work as a S- meter

Read something about audio derived AGC, maybe this is worth a try.

 

The BFO can be switched off for AM reception.

Simultaneously the input on the mixer side of the crystals is disconnected but still coupled by some capacitance of the switch wires.

AM reception is possible, but not very good.

Need to find a better solution which doesn’t degrade the crystal filter properties to much.

(By the way, the detector regen. control ads about 4 dB to the AM sensitivity)

The receiver will mainly be used for CW/SSB reception, so maybe it stays this way for a while J

 

I hooked it up to the W1TS transmitter, which was very loud.

Didn’t foresee a T/R relay (learned a lot from this project ;-)  ), so added this one between the front plates next to the RF and audio gain control.

The quit down everything a little, the RF gain pot is lifted of ground as suggested by James, N2EY at QRZ.com.

It helped a lot, but was still too loud if tuned exactly in the bandpass of the crystals.

The T/R relay now also switches an adjustable potentiometer at the input of the audio pre-amplifier.

 

The dial cord has no lag, and works very well for fine tuning.

Unfortunately the reduction drive went from 1:19 to 1:9…, the tuning capacitor only has a 180 deg. span.

Something to remember for the next receiver.

 

It’s a nice little receiver and quite stable after warm-up.

The only extra luxury a next receiver will have, is AGC.

But with no AGC it’s easier to tune the antenna tuner by ear J

There’s now a complete homebrew station here, antenna, feeder, tuner, receiver, transmitter, power supply, al home made J

 

About the Mystery Hole….

If you haven’t guessed it by now, or Pete hasn’t told you, it is revealed in one of the pictures below.

 

I also made a little video:

 

https://www.youtube.com/watch?v=4-STxQI36_s

The Invention of the Reflectometer: Naval Research Lab Report #3538

Dennis Klipa N8ERF has been doing great work exploring the technical intricacies of the humble SWR meter (and believe me, there are intricacies).   He's also been looking at the history of this invention. 

This summer, Dennis and I came across the April 1964 issue of Popular Electronics.  On pages 74 and 75 of that issue we found a clue that seemed to point to the origins of the device:  the article referred to Naval Research Lab Report #3538 by O. Norgorden,  published on September 15, 1949.  This may be the paper that led to the widespread use of SWR meters by radio amateurs.

Surprisingly, this important paper was not to be found on the internet.  Exhibiting an admirable dedication to the preservation of an important element of the radio art, Dennis wrote to Naval Research Lab and purchased from them a copy of the report.   Unfortunately, the version Dennis got had been copied and recopied so many times that it was hard to read.  So he went the extra mile and re-typed it. 

With his permission, I am giving this article its internet debut by posting it here:

http://soldersmoke.com/SWR N8ERF.pdf

Three cheers for Dennis Klipa for unearthing this important piece of radio history.

Update on the PA3GSV M4MMRX -- And a Mystery

Note the establishment of a new acronym (M4MMRX) for Lew McCoy's Mate for the Mighty Midget receiver.  We  have needed this acronym for a long time, and SolderSmoke HQ is proud to have come up with it.  We do our part my friends.

Jan has made more progress on his amazing Dutch M4MMRX and has produced a short video showing the receiver in action with SSB and CW signals. 

Here is a bit of intriguing homebrew mystery:  Jan has gone to a LOT of trouble to create that semi-circular opening in the center of the front panel.  He even cut a corresponding semi-circular hole in the sewer pipe cap that serves as the large wheel in his amazing homebrew reduction drive.  But he won't tell us what he plans to do with that space.  So I ask you, dear SolderSmoke readers:  What is that space for?  Why the see-through panel and sewer-pipe cap?  What is Jan's plan? 

From Jan:

Hi Bill,

 The rattle is gone, so I made a little video of the MMMRX in ssb and cw mode.

 https://www.youtube.com/watch?v=Ye6myxY11LA

In the text, a ch327 and a ch45 crystal is mentioned, but I can’t get this to work.

The ch45 has a 453.6 kHz fundamental, for ch327 can’t find one.

The ch327 is a FT-243 one, tested several, but no fundamental somewhere around 455 kHz.

For ssb there is a ch45 and a ch46 crystal in, which should provide a bandwidth of about 2kHz.

(Still not totally in the clear how this should work with the very narrow resonance response of the crystals.

One should expect two peaks and nothing in the middle?)

For cw I found two ch45 crystals about 130 Hz difference in frequency, which seems to work well.

Still need to correct the 40m oscillator coil, then move on to finishing the receiver.

This is my first home brew tube superhet.

The project isn’t finished yet, but it sure is fun to build, and learned a lot during the process.

73  Jan

First Signals from the PA3GSV Mighty Midget Mate

Obviously the Radio Gods (Spirits in the Sky) approve of Jan's work.  How could they not?  I can now see why he took the trouble to cut that hole in the sewer pipe cap that forms the large wheel on his homebrew reduction drive.  But what are we going to see through that center hole Jan?  What will the frequency readout be like?  
----------------------
Hi  Bill,

Just finished the last stage of the Mighty Midget MK2.

There are first signals!

The first one I heard was a broadcast station, believe it or not, the song that was on was “Spirit in the Sky” ..

All stages were built, tested and as far as possible, adjusted separately.

It was built from back to front, so the RF amplifier was last.

I added an ECL82 for more audio, the first thought of only using an EL84 didn’t bring enough.

The triode of the ECL82 as a pre-amp, the pentode as final.

Furthermore ECF82’s were used instead of the 6U8, they’re more widely available over here.

The Miller coils are hard to come by, so the 300 uH coils are homebrew.

Also used a grid detector instead of the two germanium diodes.

The triode of V1 originally intended for audio was used for this.

Made the BFO adjustable as well, still remember the screwdriver sticking out of the coil on your side... 

 

Happily there was not much troubleshooting needed.

The 80m coil was only 5 kHz off, the 40m coil 300 kHz (to low in frequency), still have to fix that.

Initially the receiver worked reasonably well without adjusting, but C1 quit at some point.

After some investigation, the problem was a dirty wiper contact on the rotor.

An ultrasonic bath fixed the problem, so no looking out for a replacement there. (hope it stays that way)

 

After adjusting, sensitivity is around -114dBm (0,4 uV) / 10 dB S/N!  (with the FT241 crystals in place, and careful tuning of the controls)

Really not bad for this small receiver, Lew McCoy was right, it really is a Mighty Midget.

I wanted to make some video’s, but over here there’s a terrible S9 rattle from 160 to 15 meters.

Every now and then it appears out of nowhere, and disappears the same way.

As soon as it is gone, I’ll make some video’s.

I made one video though, just after completing the receiver.

 

https://www.youtube.com/watch?v=CMQDYpZRkPw

 

Reception on CW and SSB sounds really well, but unfortunately didn’t record that.

The receiver is not finished yet.

Next to the 40m coil,  S-meter has to be tried, and there’s still some work on the cabinet and front panel.

 

More to follow.

   

73  Jan

PA3GSV

Update: PA3GSV's Amazing Mighty Midget Receiver (video)

Jan sent me an amazing update on his Mate for the Mighty Midget Mk 2 receiver project.  I'm really blown away by the skill that he brings to the mechanical phase of this project.   This is a homebrew dial-string reduction drive using the end cap from a sewer pipe as the big wheel.  Think about that.  Amazing. Jan reports that with the mechanical work almost done, he is almost ready to start melting solder.  FB Jan!  Check out the video above and the photos below.

Reduction Redux: Searching for Some Smooth Spin

OK, here is yet another picture of my Mighty Midget's Mate receiver, this time with yet another main tuning dial. I gave up on the large reduction drive on the right -- it worked fine but was very stiff.  I cracked open a smaller version of this very common Japanese-made reduction drive, but in this smaller one I was kind of surprised to find  a Jackson Brothers drive in there.   I now had three of these beauties available -- all of them worked fine but with considerable difference in ease of turning.  I picked the one that was easiest to turn.  

I had to cut the main shaft of the beautiful Hammarlund 35 pf variable cap that I am using. This was dangerous, because of the risk of messing up the delicate bearings.   I stayed out of trouble by putting the tip of the shaft in a vise and then cutting the shaft with a small coping saw.  This prevented any force from being transferred to the bearings.  It worked. 

I was careful to try to line up the shaft and the reduction drive as closely as I could. 

I needed something to serve as the tuning indicator.  I used one of those small CDs that often carry the drivers for cheap electronic devices.  It fit nicely.  A standard sized CD was too big. 

The final element was the knob itself.  I had an old Drake 2-B knob in my junk box (who sent me that?).  It was perfect and added a nice touch of soul to this old-new machine.

I built this receiver in 1998 and when I finished it I thought it was pretty good.  But it is much better now.  It has a nice 455 kc Toyo Crystal-Mechanical filter.  The tuning ranges on 40 and 75 now line up perfectly with the phone bands.  It now has a fuse in the power supply. And the tuning is now SMOOTH.

   

A Reduction Drive for the Mighty Midget's Mate Receiver

This morning I put a reduction drive onto the main tuning cap of my 6U8 Mate for the Mighty Midget receiver.  Before I had been directly turning the 35 pf variable cap.   The tuning rate was a bit too high for easy tuning of SSB stations.  This drive went in nicely and it does reduce the tuning rate considerably, but it feels a bit tight.   Is there anyway to loosen up one of these drives?

Bert's EMRFD Direct Conversion Receiver

Very nice Bert.  Sounds great.  I like the pill bottle coil core.  Lew McCoy used them in his designs. I do think that air core coils do provide better stability than ferrites or iron powder.   I kind of like the SW broadcast background music.  I also like the internal 9V battery.  Glad to see someone else resurrecting an old DC RX project.  


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Short Video of Mate for Mighty Midget

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A Filter for The Mighty Midget's Mate

The story of my 80/40 meter three tube (all 6U8) superhet receiver is recounted here:  http://www.gadgeteer.us/erart.htm

I've been playing with this RX on and off for many years now.  Somewhere along the line I picked up a 455 kHz filter for it (I couldn't find the 455 kc crystals that Lew McCoy used).  Yesterday I finally got around to putting the filter into the receiver.

There is almost no info on this filter on the internet.  Here are the details"
Toyo Communications Equipment Company Ltd.  CM FILTER
Type: 455 -- 2.4 -- C     Date:  8- 69

On the bottom, there are four terminals.  They are marked "P" "B" "E" and "G".   Does anyone know what these letters signify?  

 I experimented and it seemed like putting a 455 kc signal into P and B, and taking the output from E was the way to go.   I've left G floating. It works, and the improved selectivity is very evident.   But I'm operating with no specs on the filter, so I may have it in there upside down and backwards. And of course, I am operating with my usual disregard for impedance matching issues.

Here's how I've placed it in the circuit: 

Ideas, suggestions and even admonitions would be appreciated.

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

My Mate for the Mighty Midget

Al, W1UX, asked for a picture of the receiver that I used to listen to his dulcet tones this morning.   Here you go Al.    Here is an article on the project: 

http://www.gadgeteer.us/erart.htm

Above is the Mighty Midget RX paired up with a DX-60 and a VF-1 (circa 1998)


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Mighty Midget RX on a Key Chain

The key chain device will soon be carried to 1200 feet by our new rocket.

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Eddy's "Salvage Super"

I had our friend Grayson (in Turkey) in mind when I put Eddy's messages about this "thermitron" receiver on the blog.  

Here's my version of the famed "Mate for the Mighty Midget": http://www.gadgeteer.us/erart.htm 

Hi Bill,

Many thanks for the FB note...

Well, I think my buddy VE3CSK is 99% "hooked" on the notion of making an MFTMM receiver for himself---and that's a good thing. That rascal of a rig is pretty much fool-proof, & the design sure does lend itself to no end of enhancements / improvements / changes / mods! I should know: with my set-up here I added AVC, and extra IF stage, an extra stage of AF, more pre-selection, etc. etc. etc.

As for selectivity, I simply incorporated regeneration in the 2nd IF stage: with judicious tweaking of the BFO, one can achieve a near single-signal selectivity effect that is GLORIOUS on CW. I guess one can make these things as complicated---or as simple!---as we might chose to do, yet further proof of the flexibility of this receiver.

I've taken some jpegs of my set-up here, and am attaching them herewith for your perusal. I like the notion of using these rigs on 80- and 40-meter AM, too---but am presently somewhat "distracted" with the task of re-inking my main tuning dial for my 1929-style superhet.

I think my next step in my MFTMM receiver here will be the addition of an internal 125 VDC power supply---most likely will mount the components inside, on one of the vertical sides (still LOTSA room there!). I have a FB Hammond power transformer that'd be perfect for the job, & I won't have to connect / dis-connect / re-connect its current out board power supply (that I use with other peripherals, too---a REAL pain by times).

~73~ de Eddy VE3CUI - VE3XZ

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20