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Monday, September 21, 2015

Travels with a KX3

Big Bay State Park,
Madeline Island, WI
Beth and I have just returned from a short excursion to Wisconsin. We spent a couple of nights on Madeline Island, the largest of the Apostle Islands on Lake Superior and a long weekend near
Bukolt Park
Stevens Point, WI
Stevens Point in central Wisconsin. Of course my KX3 bag was one of the first things in the car.

My operating style is never highly competitive ... I find a picnic spot with a handy tree  (and, maybe, a good view), setup and then call CQ while checking the reverse beacon network to see if anyone might hear me. During this trip I was on both 20 and 30 meter CW working both coasts and as far south as MO. Along the way I also got to talk about ham radio to curious passers-by that happened to notice the wire in the tree and the techie looking gizmo on the table.

Monday, September 7, 2015

1T4 / 3V4 Regenerative Portable - continued

I've tweaked on my 1T4/3V4 regen receiver a little more. (Better headphones for more audio and fixed the bandspread dial slippage/backlash). It is now working pretty good. Here's a little demo video:

Saturday, September 5, 2015

1T4 / 3V4 Regenerative Portable - continued

I've finished my 1T4 / 3V4 Regenerative Portable. Along the way I found Dave's "Regenerative Tube Radio Building Notes" at . Dave condenses down to a few pages a lot of the information that you need to know about regen receiver design/options without spending a lot of time on theory. It fits his philosophy of "No big theory discussions or math here. You are here to build a radio, not to earn your college degree." This was helpful as I made design changes to fit parts available.

The first parts constraint I (didn't) find was a small bandspread capacitor. What I had was one in the range of 10-35pF and I was looking for something around 3-10 pF. A 10 pF fixed capacitor in series with my 35 pF bandspread capacitor got me the bandspread I needed without modifying my capacitor.

Next, the original design from Bob's Data had both low and high impedance outputs. I'm only using high impedance headphones so I replaced the 10K to 8 ohm output transformer with a 3:1 inter-stage coupling transformer. I had also hoped transformer coupling to my headphones would increase the volume...that didn't happen. More on this later.

I also decided to add an antenna coupling control. I'm not certain this helps a lot but it may come in handy when connected to a long/resonant antenna.

Finally, all of Dave's feedback control options show an RF choke in the B+ line going to the tickler coil. This seemed like a good idea. It keeps the feedback RF all at the coil rather than wandering around the chassis.

Bob's design information included coil winding documentation. I had a set of pre-wound 1930's vintage Hammarlund 6 pin shortwave coils. I used these rather than wind my own coils.

The final radio looks good and nicely covers 80 and 40 meters. I have several sets of high impedance headphones that I've acquired over the years.  My Neufeldt & Kuhnke Model D headphones gave the best volume. This is a battery set designed for A/filament voltage from a flashlight battery and B+ from a series of 9V batteries. I used my 20s battery set power supply from Antique Electronic Supply. This power supply provides the regulated A and B voltages that I needed. See .

 I'm a little disappointed in performance but this is a 1940s/1950s starter set. Maybe this is a good as it gets. Volume is low and the regeneration setting is tricky. When regeneration is set for maximum sensitivity I feel like I'm riding the crest of a wave. Any move may send the set out of CW regeneration or hurt sensitivity. What I'm seeing may be because of the tickler winding. Most references I've found indicate that the correct regen pot setting is at about 12:00. Mine is closer to 9:00...the screen voltage (and, consequently, the 1T4 gain) is pretty low when CW regeneration kicks it. Is this a problem? I don't know. The plate voltage is still the same. I'll have to wind a coil and play with the tickler winding to find out. The other limitation I found was antenna loading impact on the received frequency. Changing my antenna trimmer setting changed the frequency a lot. The solution was to add an RF stage. This won't happen. Once the C1, the bandset capacitor, is set I leave the antenna trimmer alone.

Monday, August 24, 2015

Vibroplex Model X Bug

The Vibroplex Original, introduced in 1905, is still being manufactured. For a few years, 1911 through 1923, the Vibroplex Model X was also sold. I've uploaded a Youtube  video showing the major differences between these two models:
For additional information about Vibroplex bugs see: and Tom French's book, "TheVibroplex Collector's Guide".

Saturday, August 8, 2015

1T4 / 3V4 Regenerative Portable - continued

After time with chassis punches, drill press, files, nibbler .... I've gotten my chassis finished and the major components installed. The bandset and band tuning capacitors are each mounted an inch above the chassis to allow space for the National type K dial.

Solder is next.

Thursday, July 9, 2015

1T4 / 3V4 Regenerative Portable

Since getting a 3S4 QRP midget transmitter I've been thinking about building a receiver to match it. I wanted to use tubes along the same lines as the 3S4 and, at the same time, have a late 50s style. The late 50s/early 60s ARRL "How to Become a Radio Amateur" featured a two tube regen with a 3 1/2" National type K dial. That sort of style was what I was looking for.

I finally found the receiver circuit at Bob's Data: Useful Electronic Data and Project Plans and I have a National Type K Dial to set the style.

I've found the parts I need and have played with them to figure out a layout I like. The chassis is marked up and I'm ready to drill.

Tuesday, July 7, 2015

A Ross Hull Three Tube Regen

A couple of weeks ago I spotted a radio on ebay that looked really interesting. I've been doing some research on it since then.

This radio is a three tuber with a tuned RF stage, regenerative detector and a single stage of audio  ... not unusual for an early 30s shortwave set except for the mechanical layout. All of the tubes are mounted horizontally with the RF tube projecting through the RF/Detector stage shield.  This layout allows for a compact set. The National SW3, for example,  is a three tube regen with a tuned RF stage. It measures 9.5"x7"x9". This set is only 7"x5"x6.5", less than half the size of the SW3.

A search found the original described in the June 1931 issue of QST. Ross Hull designed this set to demonstrate the capabilities of the new type 33 audio pentode.  He bragged about the gain of the AF stage and being able to drive a speaker to good volume. Why, then, didn't he include a volume control? You have to detune the RF stage if a station is too loud. Along the way, though, Hull did, in typical Hull style, came up with the clever mechanical layout. Hull was also an early VHF advocate/experimenter. This layout allows fairly short leads. I have to wonder if he was thinking ahead to 60MHz when he sat at the drawing board designing this radio.

Sunday, May 3, 2015

Spring 2015 in the Park

It is warming up nicely here in SE Minnesota and the city parks are finally open. Yesterday I took my KX3 along with my 20 meter end fed zepp to Essex park here in Rochester. I didn't have a lot of action but both QSOs were neat. I finally had to QRT when the high school kids started showing up for prom photos and it looked like I might be in the background.

My first QSO was with NM5S in the Magdalena Mountains of New Mexico. He was operating SOTA (Summits on the Air). I've activited a couple of summits but no 10 pointers like Alan was yesterday. Later this summer I'll probably find a summit or two to activate myself.

My second QSO was with N1SZO. Rod was running 170mW using a
Rockmite transceiver and a 1/2 wave vertical. He was almost 100% copy here in MN, that's 5600 miles per watt!

I'm looking forward to more QRP outings to the park but next time I'll pack along a Coke and the BBQ grill so that I can make a day of it.

Saturday, December 20, 2014

2014 Bruce Kelley 1929 QSO Party

It was an interesting Bruce Kelley 1929 QSO Party this year. I learned a little more about using my own 1929 equipment and greater appreciation for the skill of those hams 85 years ago.

Getting my SW5 on the same frequency as my transmitter was the greatest challenge.
Fortunately I could tune my KX3 to my transmitter frequency using the KX3 as my code/signal monitor and then get the SW5 on frequency by tuning it and listening for the KX3 local oscillator.

I was never totally satisfied with the stability of my Hartley but, in reality, it may have been good enough of the BK. At the last minute I switched it out for my TNT. My TNT is a push-pull design with two tubes is push-pull across the tank circuit. Any inter-electrode capacitance change is cut in half so drift due to this capacitance change is also cut in half.

As mentioned earlier I tamed my SW5 considerably by converting the tuned RF stage to an untuned RF stage. This required only plugging a new "coil" consisting of an RF choke and capacitor.

All in all I made 16 contacts on 80 including Maine, British Columbia and North Carolina....not too bad for my 2-3 watts into a low endfed wire.

My friend W7BGO caught me on the air and recorded two of my QSOs, one with K0EOO and the other with KE0Z.

Listen to recording of my QSO with K0EOO and his 1926 Hartley:

Listen to recording of my QSO with KE0Z and his 1929 Hartley:

Thursday, November 6, 2014

2014 Bruce Kelley 1929 QSO Party

I'm making progress with this year's 1929 QSO party station. The SW5 works OK but I wonder if the grounding may have gone bad over the years. Nothing in the 1930's SW-5 literature hints at the sort of microphonics and feedback that I'm experiencing. I've tested the bypass caps by substitution and tightened all of the nuts/bolts I find with no change. Running it with an untuned RF stage seems to be the biggest help. Next is powering up my 1928 Hartley.

Pictured is my SW5 at the operating position and Hull Hartley on the window ledge. My Hartley tends to be microphonic because of the tank circuit construction. It can't sit on the operating table because just pounding on the key will be transferred to the transmitter causing the signal to wobble. The window ledge sits on the cinder block house foundation. it shouldn't be going anywhere. I'm using a National 5880-AB power supply (recapped, fused and cord replaced) with the SW5. The regulated power supply is for the Hartley...anything to make the signal as stable as possible. Also part of the station is my Elecraft KX3. The BK recommended operating windows are only 25 KCs wide, just a couple of dial divisions on both the SW5 and the Hartley. The KX3 will be my frequency meter and backup receiver.