Sunday, August 31, 2014

Telford Rally Weekend

This weekend was the annual Telford Radio Rally that is held at the The Enginuity museum at the Ironbridge Gorge. This area also has a lot of interesting museums so it was decided to make a weekend of it. We drove up Saturday morning, following the Tom Tom route that was an alternate to the motorways which visited lots of back roads and no towns! First we went to the Coalport China museum, then the Tar tunnel and finally the Jackfield Tile museum before retiring.
Sunday morning we followed the very noticeable Fluorescent road signs to the rally and parked in the adjacent AGA works (of stove fame)  to the Enginuity complex.
There were a selection of stands outside in the courtyard and more in an inside hall. I bought a 12v 7AH SLAB to power the KX3, guy rope, an EF183 (for my PW 6AF11 RX) and an 8W 6cm amplifier (from the G3OHM club stand). I did resist the British Tube tester for 250 pounds! I spoke with Gordon, G8PNN who I had not seen since staying overnight at his place on the way back from the GB2YS/GB2ZR expedition in Aug 1986...he still remembered the car I had!
After the rally we walked uphill to the Darby House museum which were also very interesting. On the way back to the car we noticed the date the Rally building was built, you never see such age at USA hamfests! 
When we got back to the Rally carpark we were the last car there:-

Saturday, August 9, 2014

KX3-2M KX3 144MHz Internal Transverter

The KX3-2m module is lower left
I ordered this during Dayton and it arrived this week after 3 months. It took about 20 minutes to fit into the KX3. Measurements showed 2.5W output off 13.8V and the W5HN/B beacon was audible on a whip attached to the SMA antenna connector, so sensitivity seems ok.

I originally also ordered a 4m transverter module, but after seeing warnings about the limited number of times the two RF cables interconnecting the modules to the KX3 could be plugged/unplugged, I gave up on the idea and reverted to the external 70MHz DEMI Transverter
Closeup of KX3-2m module

Friday, July 18, 2014

432MHz Solidstate Amplifier Completed

Over 3 years ago I bought a W6PQL 432MHz amplifier module  with the matching LPF/Directional coupler. Before I moved out of the McKinney house I quickly mountedthe modules on a heatsink inside an aliminium chassis to protect it in storage. Over the last few weeks I have finished the metal bashing thanks to WA5YWC and built a PIC controller and LCD display.  The biggest issue was testing it as I no longer had a 432MHz transmitter in the USA. W5LUA kindly offered to let me use the facilities in his shack which included drive source, Power meter and dummy load.
The first thing we learnt was that the RF got everywhere inside the chassis. Initially there was no screening around the PIC board which caused measurement issues. After a trip to the local hobby store for some .015" ali sheet and the donation of many 1nF bolt in feedthroughs by W5LUA that issue went away. It was necessary to put a screening can over the directional coupler (W6PQL only suggests it for his 1kW amplifier) as the calibration of the bargraph meter changed dramatically when the cover was put on the box
When completed the amplifier gave 420W for 6W drive when running 17A at 48.0V. Looking at the W6PQL figures I could hit the amplifier harder to get the full 500W but this way I have a safety margin. All harmonics were over 65dB down on the fundamental power.

Monday, July 7, 2014

Fujitsu 251-9735-010 6GHz amplifier fixed

I was given a Fujitsu 251-9735-010 6cm 5W amplifier by WA5VJB about 12 years ago for my Transverter but never got round to trying it out, this weekend was an opportunity. I borrowed a 5760MHz California Microwave brick which gives 16dBm at 5760.000MHz from W5LUA to save needing to retune my DB6NT 5616MHz LO. This needed a -19V supply, provided from my 57A 28V PA supply (yes overkill!) According to Kent's notes the PA needed 4A at 12V and 200mA at -12V for the bias for which two other additional PSUS were found (a variable one and the 13.8V rig supply). Applying the -ve bias the power supply immediately current limited, but the resistance to ground from the bias supply lead was 12kohms. Time to take the lid off. LOTS of screws later the lid was off. The -ve bias supply feeds a 7905 regulator. As a quick test (to avoid more screws) the regulator was cut out and the -5V applied to the regulator output pin. With the 12V supplied 5W was seen. The control board was removed and a new regulator fitted. It still produced 5W. 
The opportunity was taken to measure some voltages and currents. Full output was produced until the positive supply dropped below 12.00V. Full output was produced until the negative bias dropped below -6V, The measured currents were 12V at 3.9A and -12V at 50mA. It was noted that the detected output was a negative voltage. Not good for Microchip PICs! The detector diode was reversed and resistors adjusted so that the detected output was +10V at full output. 

Thursday, June 19, 2014

Hamcom 2014

June brings the annual Hamcom hamfest to Dallas, which, as always clashed with the ARRL June VHF contest.

As in the last four years I volunteered to help man the Elecraft Booth, this year with Eric WA6HHQ and wife Lerma. Their plane got diverted from DFW to AUS as DFW closed for an hour due to bad weather so we didn't start setting up till 5pm Wednesday. 

The trade show exhibitors this year started earlier at 0800 and officially closed at 1800, making a long day. The new item this year was the PX3 Panadaptor for the KX3.
 The K3/0 mini was also in evidence, this time using the software from, to control a K3/KAT500/KPA500 in California. It was great fun on the Saturday afternoon listening to the 6m activity in California during the VHF contest.
 The outside flea market was not too exciting. The most interesting item was a Layafette tube tester without model number. I was told that Lafayette often rebadged other companies products.
 I also got some tube bases, some tubes for my BBC studio-E receiver and a multiband whip for the 2m module

I did get to meet John Langridge. KB5NJD who also operates on LF as WG2XIQ and compare notes from WH2XES. Unfortunately I could not get to his talk on reusing "normal" HF antennas on 477kHz.

UPDATE: The Lafayette tube tester is a Accurate Instruments model 157 in disguise

Friday, June 6, 2014

DrugStore Tube tester...every shack should have one!

To help me restore the Country Belle radio I wanted to test the tubes.  I mentioned this to Roger N5PGH at the NTMS Tuesday BBQ meeting. At the next meeting he appeared with a loaner tube tester in the back of his truck. This was a "Seco Electronic Tube Analyser"  It was the type often seen in your local USA drugstore in the tube era so you could test the iffy tubes in your radio receiver and they would sell you a replacement. This one had been previously built into a panel but was now mounted on a undersized box.

It has a meter, switch,  variable load resistor and 92 sockets. It came with a manual of what settings to use for each tube.

All the tubes in the country Belle radio passed with flying colours. along with some other 1930 era tubes I had acquired for future projects.

I had been looking for a 6AF11 audion multistage tube for a while. WA5VJB found me one in the Dayton Hamvention fleamarket. The manual had 3 settings for the tube so decided to test it. Two settings produced good pass results of 120 but the third only produced 20, a big fail. Pity! I then remembered that Roger had mentioned the tube tester can be used as a reconditioner by leaving the tube in its test configuration overnight. Worth a try. The next morning the reading was 100, so I let it be for the rest of the day which restored it to a 120 reading. What a great tool, even if it is so large! I will be looking for a transportable tester.  

Restoration Project: Country Belle 1956 Radio

Having built a couple of one Tube receivers, a local amateur decided it was time for me to move on to a restoration project. As a challenge he presented me a while ago with his spare Country Belle Radio #556  made by Guild in 1956. This radio was made to look like the old style wall Telephone, but had a 5 tube medium wave receiver Inside. Taking the earpiece of its rest turns the radio on. The Winding crank is the tuning knob, very neat. It had some hardware missing (a bell, the tuning crank and the earpiece rest) but was electrically complete.
The Tubes lineup is the classic "all American Five".  Converter: 12BE6, IF amplifier: 12BA6, Detector: first audio amplifier: 12AV6, Audio power output: 50C5, Rectifier: 35W4. The subtlety of this lineup is that the filament Voltage/Current all add up so you just connect them all in series across the 110V AC (or DC) supply. The 35W4 even has a tap on the filament to drive a dial light (#47)
As the radio is transformerless,  for safety I borrowed an Isolation transformer from WA5VJB. When power was applied, all the heaters lit up, there was some noise but no stations could be tuned in. Tracing the circuitry I found that the grid Transformer of the 12BA6 was open circuit. The Inductor was taken apart and the wire mended. Now when powered up stations were loud and clear. I peaked up the 455kHz IF Transformers, noting that each transformer had an upper AND a lower tuning core.
Next task was the Hardware. Luckily a friend of a friend had a carcass in their barn which I was given. The wood work was bad but it had all the missing hardware.
The next decision was what do about the woodwork. Sand it down and repaint or leave it in its current patina state. In the end I decided to sand down all the wood parts (after stripping the fittings) but this also removed the Decals. I then sprayed it with Pecan wood stain/Varnish (3 coats). The Brass fittings were cleaned with Brasso (which I discovered is sold in the USA) then varnished. It was recommended to spray the other black metal fittings with Black Lacquer, but using it can be challenging. I went to the local O'Reilly's autoparts store to get some but after explaining what I wanted it for to the Old Guy, he said not to use it but to use Black "Dupli-color Vinyl and Fabric Coating" as It would flake less. This has really worked well
I found a source of replacement decals at These were water based transfers (like I used many years ago for Airfix model aeroplanes) which were a little tricky to apply, but I managed it. When dry the cabinet was sprayed with Varnish
When completely reassembled,  the radio worked fine and looked very nice, even though I say it myself!

The restored external view


The restored internal Electronics
The good news is that I found a small 240V/120V transformer that will will allow the unit to be used in England, so it has been dismantled ready for shipping