HT-37/2B QSO with K6ZA (three short videos)

On January 23, 2019 on 20 meters I talked to Barry K6ZA.  He is near San Francisco.  I was running my Hallicrafters HT-37 with my Drake 2B.  I was really pleased to discover that the guy I was talking to loves these two pieces of gear as much as I do.  

Barry said he wished I could record his voice coming out of the HT-37.   My iPhone came to the rescue.  

The Secret Life of Machines -- Radio

We had this on fhe blog three years ago, but it is so good that it deserves a second posting. 
Thanks to our old friend Stephen Walters for reminding us of this gem.  There is so much soul in these old machines. Thanks Stephen. 

Godzilla, an SP-600, a D-104, and a Turner SSB+2 Transistorized Mic

We were in a restaurant last week and this trailer played on a TV that was all the way across the room.  The SP-600 caught my eye.  I once had one of those, but chickened out when I read about the horrors of black-beauty cap replacement.   There is also a D-104 in the trailer (several of those are with me now).  And the girl is transmitting with a Turner SSB+2 Transistorized mic -- I have one of those also. 

Thomas K4SWL over at The SWLing Post  notes that the SP-600 Tuning Dial appears to have been modified.  I'm thinking the wanted it to look like some sort of transmitter output meter. 

I think I can also see some sort of Collins antenna tuner.   

Any ideas on whose shack this all comes from?   It looks like a real ham shack.  

From the trailer, it appears that the ham gear somehow helped us establish contact with Godzilla, who then went on to save the planet.  I hope.  ONCE AGAIN, HAM RADIO SAVES THE DAY! 

The ham radio stuff is in the first minute or so of the trailer. 

Rescued at Sea! Saved by an S-38!

Just click on the ad to enlarge it. 

Another cartoon relayed via the Facebook page of Jeff Murray K1NSS.   

Sure, there was a rescue at sea, but what about all the casualties caused by the AC/DC "widow-maker" S-38 power supply? 

When Hams Wore Neckties, and AM Transmitters Were in the Living Room

Jeff Murray K1NSS had this on his Facebook page.  Great stuff.  But I felt like yelling out, "Stay in the basement OM!  Stick with your haywire rig!" 

A Homebrew HRO Dial by DL6WD, Homebrew Hero

Take a look at that beautiful rig in the bottom of the cover pictures. (A closer shot appears below.)  That is an HRO dial, right?  Or is it?  

No, it is not.  In the picture we see the homebrew receiver designed and built during the 1960s by Rudolf Fishcer, DL6WD.  It is magnificent in every respect.  Because I have been working with the HRO dial and gearbox given to me by Armand WA1UQO, the tuning dial on this receiver caught my attention. 

Here is what DL6WD says about this part of his project:  "The main tuning gear was built around a BC-221 tuning capacitor and reduction gear. The counter dial and tuning knob are the result of four weeks of labor, The counter dial reads in tens of kHz, where the main tuning knob has a calibration of 200 Hz per division, from an HRO inspiration."  The counter is in the little window to the upper left of the tuning knob. The window to the upper right is a phase-lock indicator. (See below.)

By the way, by the time DL6WD got finished with this all solid state receiver it weighed in at 52 pounds.  Rudolf noted that "excessive shielding pays in electrical performance, but not in weight!" 

DL6WD earns the title "Homebrew Hero."

Switching to a Mechanical Filter from 1967 for my HRO-ish Receiver (with video)

From RSGB Handbook 1982

Having overcome the difficulties with the National NPW Dial and Gearbox, I turned my attention to the 455 kHz filter.  I had been using this old Toyo CM - 455 kc filter (Date stamped August 1969).  CM stands for "Crystal-Mechanical."  These filters are hybrid with some of the features of a crystal filter and some of the features of a mechanical filter. For more details go here: 
https://soldersmoke.blogspot.com/2016/04/the-meaning-of-cm-in-toyo-cm-455-filter.html

I was disappointed by the CM filter.  It seemed very lossey, and it just didn't seem to be of sufficiently high Q -- it seemed very broad. I could hear the other side of zero beat.  It was barely a "single signal" receiver,  and being "single signal" is the whole point of a superhet. 

I remembered that Pete Juliano had sent me a Japanese-made 455 kc mechanical filter. Maybe this would do better.  Last night I did a quick comparison test and -- wow -- Pete's filter was much better.  The Fifth Edition of the RSGB Handbook seems to agree with my assessment, noting that mechanical resonator filters were superior to the Crystal Mechanical hybrids (see pages 4.17 and 4.18) 

Pete's filter is from the Kokusai Electric Company.   Part# MF 455 ZL.  (Date stamped May 1967). "ZL"indicates lower sideband.   I checked and indeed the passband goes from just above 452 kc up to about 454.5 kc.  This is a 40 meter receiver and SSB on 40 is LSB, so this filter would work perfectly right?  Not so fast!  Sideband inversion had to be considered.  

I was running my VFO from about 7455 to 7755 kHz.  This means that the modulated incoming signal would be SUBTRACTED FROM the VFO signal to get to  the 455 kHZ IF.  And when that knd of subtraction happens, we have sideband inversion.  The LSB signal will look like a USB signal when it reaches the filter. 

My BFO was running right at 455 kHz, using a ceramic resonator at that frequency. I briefly considered just shifting it down to 452 kHz, but this proved to be difficult.  Then I got a better idea. 

I could just shift the VFO down to 6545 to 6845 kHz.  This would mean that the VFO frequency would be subtracted from the incoming modulated frequency.  There would be no sideband inversion.  I had been thinking about doing this frequency shift anyway, thinking that VFO stability gets better as you go lower in frequency. 

REMEMBER THE RULE:  If you are subtracting the modulated (signal) frequency from the frequency of the local oscillator or VFO, only then will you have sideband inversion.  See: 
https://soldersmoke.blogspot.com/2015/05/sideband-inversion.html

Moving the VFO was easy. I am using a variable capacitor with several variable caps on the same rotor.  I just moved from the smallest variable cap to the middle variable cap -- this added capacitance to the system and lowered the frequency.   I also added three additional turns on the coil.  This put me very close to where I needed the frequency to be.  I added one additional 9 pf cap and this put the VFO freq right where I wanted it. 

I was really  glad to include Pete's filter in this receiver.   The mechanical resonator technology fits very well with the very mechanical old-tech theme of this project (it already had a gearbox -- a mechanical filter seemed to fit right in).   It is a fascinating device -- it is almost like having a set of tuning forks all tuned to 455 kc (see above for the RSGB description of how it works).    And having it from from Pete adds a TREMENDOUS amount of mojo, juju, and soul to the new machine. 

Icing on the cake: As I type this, I am listening to Fred K3ZO converse in Spanish with hams all through South America.  Fred preceded me by three decades at the U.S. Embassy in Santo Domingo, but when I got there the local hams were still talking about him  -- he was much loved and admired by the Dominican hams.  TRGHS. See Fred's story here (scroll down a bit): http://www.gadgeteer.us/DRDISP.HTM