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Saturday, April 30, 2016

KC9KEP's Superhet Receiver with HOMEBREW 455 kc IF Transformers



No store-bought 455 kc IF cans for Big Nick!  FB OM.  Great stuff.

We have featured Big Nick's beautiful work twice before:

More of his videos here:
Be sure to check out his coil winder.

Friday, April 29, 2016

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.

   

Tuesday, April 26, 2016

Always Listen to Pete! Second Thoughts on the S38-E


After working a bit on the Hallicrafters S38-E receiver, I am forced to admit that Pete was probably right about this receiver when he warned me that I'd be putting lipstick on a pig.  For those of you who have a sentimental attachment to this receiver, please don't take offense -- I understand.  But while I had one of these as a kid, I never really BONDED with it. That Drake 2B was stiff competition for my radio affection. So I can be more objective about this thing.  And I now think Pete was right. 

Problems: 

-- It is mechanically rickety.  It jiggles around mechanically and, as a result, electrically.

-- The front end is no match for Northern Virginia RFI.  All it has between the antenna and the converter tube is one puny LC circuit.  Not enough.

-- The LO mixer and the LO are stuffed into one 12BE6 tube.  The IF amp and the BFO cohabitate in another tube. In each case there  just seems to be too much going on between one plate and one cathode. 

-- The whole AC/DC transformer-less thing is kind of nuts. You have to get used to TWO ground symbols on the schematic: one symbolizes B- (and is not attached to the chassis).  The other is to chassis ground.  Turns out that my E model is not really a "widow maker" -- they have a 470K resistor and a cap between B- and chassis ground, so the damage you could do to yourself was quite limited.  Still, it is all kind of goofy.  I have an isolation transformer on the chassis, ready to move this receiver into the 1960s if the spirit ever moves me.  KB2WIG commented:  "At closing time, I don't care if the S38 has lipstick."  

As I worked on this thing, I began to realize that the little homebrew 6U8 receiver I have next to it on the bench is a much better receiver.  So I began to lose enthusiasm for putting lipstick on the S38-E.  At least for the moment.  I do like the cool 1950s place names on the S38-E's front panel:

Java
USSR
Vatican
Singapore
Edmonton (!)
Congo
Milan
Iceland
Angola
And of course, the CD (Civil Defense) frequencies. (For when you wanted to do some shortwave listening while ducking and covering. )

But for  now, me and the S38 are on a break. 

Saturday, April 23, 2016

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?


Wednesday, April 20, 2016

Meeting up with ARRL CEO Tom Gallagher, NY2RF

On April 12, Tom Gallagher NY2RF was in DC and was kind enough to make some time in his schedule for us to get together and talk about radio.  As we mentioned on a recent podcast, Tom, who has recently taken over as Chief Executive Officer of the American Radio Relay League, is a true FB ham.  He has a restored Drake station that he keeps on the air, and was recently talking up the Michigan Mighty Mite during his interview with Eric 4Z1UG in the "QSO Today" podcast.  And he is a SolderSmoke listener.  It was great to finally meet Tom.  We are all lucky to have him at the ARRL.

Tuesday, April 19, 2016

Pigs, Lipstick, and my old Hallicrafters S38 "Widow Maker"


I blame Grayson for this.  After getting my old 6U8 superhet running nicely on 80 and 40, my attention turned to an old Hallicrafters S38-E that had been relegated to the car port (Armand saw it out there, looking abandoned.)  I didn't like it because of its "transformer-less" "widow-maker" power supply. I was afraid to even GIVE it away for fear that someone would electrocute themselves.  But Antique Electronics Supply had an isolation transformer, so the order went in.

I have to rewind or replace one of the primaries on the input antenna coil.  This was a victim of the original cheapo power supply.  Apparently the antenna terminal got grounded when the chassis was "hot."  POOF -- smoke was released.    

The bands do seem to sound better through thermatrons... And there is an undeniable 3-D aspect to working on these old rigs.

So yes, in a certain sense  REAL RADIOS GLOW IN THE DARK.

.............

Bill, I think that as long as you don't work on it in the car port in your bare feet you'll be fine!  Good luck with it and don't blame Grayson too much.  I think it was destined to come back in the house eventually.  The radio gods have been whispering in your ear!
 Ciao! & 73, Armand

............

Bill:
I’ll take the blame, no problem!
S38 is nice to work on, plenty of room, no magnifying glass required.  But I have to admit I am not a big fan of working on low cost AC line powered “raft-anchors” (too little for a boat).  Definitely give it a isolation xformer and replace the filter cap(s).  If it doesn’t weight 50+lbs, a bit lightweight for me.
If you need a good thermatron homebrew project (and who doesn’t really), I’ll send you plans for a nice 4-thermatron (including compactron) AM/CW 20/40M 5 watt transmitter I am finishing up (90% of the work is “finishing up”).   Designed from scratch.  Actually works.  Uses a new construction technique I’ve been working on. 
Grayson
..........

Hi Bill,
As I read about your next project – kept thinking –you can put lipstick on a pig BUT it is still a pig. I had one and put an isolation transformer on the front end –but found I was showing signs of carpal tunnel syndrome on my left hand as I kept retuning the radio because it drifted so much. Have fun.
Pete

Pete:
I don't know.  Simplicity is a virtue, and this thing is pretty simple: RF amp, mixer, LC oscillator, detector, audio amps.  Broad as a barn door with just two 455 kc IF transformers for the filter. Lots of room on the chassis. 
As for drift, my little 6u8 RX with LC oscillators in both LO and BFO settles down very nicely. 
Bill
...............

Hi Bill,
 I surely didn’t mean to denigrate your next homebrew project and perhaps it was that the one I had was a  dud in the lot.
 But I then moved up to the SX-99 and was in tall clover. Besides today we have some things we can do to enable “tamer” oscillators. So why not? You need to team that up with the M^3 and make some contacts.
 Pete
.............

Pete: I KNEW  you would try to get a synthesizer of some sort inside the S38-E.  But I say NO!  I had a lot of fun getting the LC oscillators in my 6U8 rig to tune exactly where I wanted them to tune.  You know, play around with the cap in series with the main tuning cap to change the tuning rate (better than removing plates -- they are hard to put back on!).  Then changing the values of the L and C elements to get the thing to oscillate in the desired range.  Then wrap it all up with some Dymo tape on the 1/2 CD "tuning dial."   Sure, I know, that would have been a few keystrokes on the Arduino, but somehow this old way puts you closer to the physics, closer to the electrons. Take a look at the e-mail about Wooden Boats, VFOs and PTOs on yesterday's SS blog. 

The "widow maker" potential of the S38-E was apparently on the minds of the guys who designed the cabinet. The whole box and the front panel are all very carefully insulated from the chassis.  Plastic nuts!

Nice looking pig, by the way.  She may appear on the blog soon. 

73  Bill



Monday, April 18, 2016

Wooden Boats, VFOs and PTOs -- Recovering Lost Arts

Sunday, April 17, 2016

K.P.S. Kang's Pixer Superhet



K.P.S. Kang (VU2KR and VU2OWF) has been contributing ideas and circuits for many years from his QTH in Punjab India.  He is the source of what became known as the VU Transmitter circuit:
http://www.zerobeat.net/g3ycc/week1.htm

Today I spotted a recent blog post by OM K.P.S. on a simple superhet receiver he is working on.  He has a knack for describing the design considerations (needed gain, IF selection, etc.)
Check it out:

http://smallwonderqrp.blogspot.com/2016/04/pixer-empirical-hf-superhet-receiver-i.html

and

https://plus.google.com/111066147552844651495/posts

Friday, April 15, 2016

WSPR Party Balloons Make it Across the Pond


   
Hans Summers
April 15 at 11:25am
 
VE3KCL/QRP Labs S-9 balloon finally reached Europe! What a crazy way to cross the Atlantic. Crossed Portugal, now into Spain. France is next! 16mW 30m WSPR signal was reported in ZL and VK (19,000km DX). Who says you need 5W on HF WSPR? 73 Hans G0UPL http://qrp-labs.com

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