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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. See it here: //www.youtube.com/watch?v=y-tRmDAmf3o

For additional information about Vibroplex bugs see: http://www.vibroplex.com/ 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.

Friday, October 24, 2014

2014 Bruce Kelley 1929 QSO Party

This year's AWA 1929 QSO Party is only about  1 1/2 months away.
The Feb 1931 QST cover inspired me to pull my SW-5 off the shelf to pair with my Hartley transmitter.

I found feedback within the SW-5 to be a problem. This isn't too bad for casual listening but it is a real problem for  on-the-air operating. Checking through my QST files I found the James Millen Sept 1931 article describing the design process for the SW-3. In it he talks about various shielding options. The SW-5 shielding looks a lot like Millen's first attempt at SW-3 shielding. He described the results as "most disappointing" and "the RF stage oscillated violently". My no holes solution? Turn the tuned SW-5 RF stage into an untuned RF stage. I inserted an RF choke and an antenna coupling capacitor into an empty SW-5 coil form and use it instead of a standard RF stage coil. Now the SW-5 RF stage stays out of oscillation and it still picks up plenty of 80 and 40 meter signals.


It looks like I may be able to use my new QSL cards after all.

Friday, September 12, 2014

Special Event Station K0M

A major focus for my spare time this past spring and early summer has been putting a special event station on the air. We ended up making 214 contacts over five days. See http://radiok0m.wordpress.com/  for the details.

The equipment and focus wasn't particularly vintage or QRP (unless you count the 25 year old Heath SB-1400) but I did try out a new antenna (a MFJ-1777 102' center fed (with window line) doublet) and now I know more about setting up a special event station.

One advantage of a special event station is that there are no contest type rules. You can put as much into it as you wish. It could certainly be used to introduce other local hams to QRP operating or vintage equipment. A 1x1 call can even be reserved at http://www.1x1callsigns.org/ . Fortunately WB4AEJ's posting at  http://forums.qrz.com/showthread.php?444979-Planning-and-Operating-a-Special-Events-Station-2014  covers a lot of the how-tos.

Wednesday, May 28, 2014

Function again wins

80 years ago crystals were expensive. Hams made do with one or two. Ads for the Utah Jr even touted two crystals will cover 160-20 meters. Swapping crystals to QSY up and down the band was not a high priority. The Utah Jr reflects this design philosophy. The one crystal socket is accessible only from the back and sits just in front of the plate loading cap with B+ exposed. Just the other side of the 6L6 is the plate loading coil with the same B+ exposure. Safe operating practice requires one to power down this transmitter before changing the crystal.

Today most hams have transceivers, they expect to hear a response to a CQ on their frequency. If I don't have a crystal plugged that puts me close to a station calling CQ he isn't going to hear my call. Powering down the transmitter to swap a crystal out takes time tempting me to cut corners.

The obvious solution is to extend the crystal socket so that I could change the crystal without digging in to the rig. I ended up building two versions. The cute one shown included 8" of TV twinlead and two crystals sockets wired in parallel. It sat on top of the Utah Jr making it easy to change crystals. The functional one had only  two wide spaced 3" leads running from a male 5 pin plug (that fit the Utah Jr crystal socket) to one crystal socket barely beyond the back of the transmitter. Running with the cute one resulted in a chirpy, harmonic laden signal while the other gave a clean signal. The cute one added about 7pf in parallel with the crystal while the functional one only added about 2pf. Maybe the extra 5pf causes a problem or maybe RF is feeding back via the 8" of twin lead. Either way, function wins over cute.