Had an interesting X-Band contact on Tuesday night with Ross G6GVI. I set up the 13cm converter and antenna in my garden and we arranged a X-Band QSO between 13cm and Topband. I transmitted on Topband and Ross transmitted on 13cm. Copied Ross at about S7 on 13cm. Later, I listened to the UKAC contest and heard some stations. This is my first encounter with 13cm, maybe I will have a go at building a transmitter.
Here is a photo of the 13cm set up in my garden.
Some photos from Sunday’s contest with the Bolton Wireless Club at Horrocks Wood. An enjoyable day, 75 contacts and it didn’t rain!
For my next renovation project I would like to have a go at an Eddystone receiver. These classic receivers were produced in Birmingham just after the war and they produced many different models. The early models used a mains transformer for the PSU, but later ones were AC/DC which meant that they did not have an isolating mains transformer and used a mains dropper like the old TV sets. These models are dangerous as the chassis is not earthed and is liable to become live. After some careful research I decided that the best model for renovation would be the S640, S680 or S750. I particularly like the S750 because of the classis Eddystone 898 style of dial.
After a while I came across a very sad looking S750 on E-Bay that needed a lot of TLC, but for £50 I thought it would make an ideal project. I managed to secure it and was delivered in a huge box!
Cosmetically, it was in a bad way. The receiver had been stored for a long time, the finger plate, selectivity knob and drive coupling were missing and the paintwork was very poor. Inside, the chassis and valves were all in good condition and underneath the original components were intact, but the soldering of some of the wires needed some attention. The drive mechanism was very dirty and not working correctly. This was going to be challenging project!
So where do start? Well, first of all removing the case and front panel so that I can see clearly the work involved. There are lots of information about restoring Eddystone receivers on the Eddystone Users Group and forum. Some great stuff written by Gerry O’Hara, which takes you through the renovation of an S750. At this stage I had no intention of powering up the receiver. Instead I checked the resistances of the mains transformer and choke, everything seems fine.
The front panel includes the 898 style drive mechanism, which of course will need a lot of work later. I decided to put this to one side and concentrate on the main chassis first.
The chassis was caked with dirt and nicotine and quite smelly, a good clean was necessary. Using a wire brush, isopropyl alcohol and metal polish I set about cleaning above the chassis.
Inspection of the Power Supply unit made me realise that it was a rats nest of wires that needed removing or replacing. The smoothing capacitors were bubbled and needed replacing. The smoothing choke was not original and had been poorly fitted above the chassis, likewise the audio output transformer. I decided that a complete rebuild of the Power Supply unit was needed.
I drew lots of diagrams and took many photos of the wiring before removing the PSU from the rest of the receiver. I was then able to work on the unit by itself. A lot of the wiring was to the octal sockets on the rear panel which is no longer necessary, so I could remove most of it, which I did. The octal rectifier valve had been changed for an unknown four pin rectifier valve. I removed this and used a couple of IN4007 for the rectifiers instead. A new smoothing block and new capacitors and resistors used to replace the existing ones. I also replaced the wiring sticking to the original colours. Testing the Power Supply gave me 300v HT and 150v regulated along with two 6.3v heater supplies.
While rebuilding the PSU the underside of the chassis was cleaned.
Now it is time to move on to the RF / IF and audio stages. The RF unit is in good condition, the components are very difficult to get to, so I will leave this alone unless there are any faults that emerge when it is tested. The IF and audio unit can be separated from the rest of the chassis (like the PSU) this needs most of the resistors and capacitors replacing. It was quite easy to work on and most of the decoupling capacitors were bolted onto the chassis. They just needed unbolting and then replacing with up to date components.
Once this was completed I could assemble the whole chassis back together again and re-fit the front panel ready for testing.
I Powered up the receiver while monitoring the HT voltage, after a while I heard a faint hum from the speaker, but nothing else. After some investigating I realised that I had made a wrong connection to one of the switches. When I repaired the connection, the receiver sprang into life!
All the switches and controls appeared to work apart from the BFO. I was able to listen on 80m, but couldn’t resolve the SSB stations. Note that the drive mechanism was not working, I tuned in stations by moving the arm on tuning gang.
One thing that I did notice was that audio was quite low and also when I switched on it took a long time before coming on. I checked the heater voltages, there are two 6.3v windings on the transformer, one gives around 3A and the other, which only supplies the noise limiter valve, is only rated at 300ma. The main heater voltage was down to 4v, but the other was fine. It turned out that the two 6.3v windings were connected the wrong way. This was wired like this when I got it. Swopping the windings over cured the problem, now I have lots of audio and the valves warm up quickly.
I now moved on to looking at the cosmetic problems and drive. I became aware from the Eddystone User Group that some components are still available for these receivers from Ian Nutt, who has a stock of parts. My first step was to message Ian to see if he had any spare parts to replace the ones missing from my receiver. I needed a finger plate, drive coupling spring, selectivity knob and also two drive chord spools. Ian managed to find some of the parts, particularly the spools, which would have been difficult to replace. Ian didn’t have a finger plate, so I solved this by using a template from Gerry O’Hara to have an aluminium sign made by a printing company called ‘Helloprint’. This was not perfect, but acceptable.
The drive mechanism is quite a challenge, stripping down the front dial and drive chord is a bit scary! Never the less I managed to complete it, replacing the chord spools and also the drive chord, which was too thick. I bought some 7 strand, steel Pike wire from a fishing shop. This was used in the original receivers. The drive mechanism itself was thoroughly cleaned and polished. I lubricated the bearings with machine oil so that it would run smoothly. The drive is pleasure to use!
Connecting the drive to the tuning gang needed some thought, the spring that holds the ratio arm to the spindle is still missing. I managed to fabricate a new one from some steel wire. Again, not perfect, but acceptable.
I painted the front panel and case with VHT Wrinkle paint, it worked quite well and I now have a nice wrinkled finish. Before re-assembling the front panel I replaced all the original switches with new ones.
The receiver is now working fine apart from the BFO and a problem with Band 1, which doesn’t seem to be working. First I had a look at the BFO module and stripped it down, it appears to be working, but may not be on the correct frequency which should be 85Khz. Checking the frequency on an oscilloscope confirmed that the BFO is working, but why can I not hear a beat?
Well, this turns out that the S750 has a terrific amount of RF and IF gain, so having the gain controls turned up completely swamps the very low level BFO injection. Gerry O’Hara explained to me that the correct use of the receiver is to keep the RF and IF gains turned well down and the Volume Control turned up. The volume is adjusted using the RF and IF gain controls when listening to SSB or CW. This solved the problem!
Next, why is Band 1 not working?
Investigating with my oscilloscope revealed that the mixer oscillator on this band was not working. Further investigation tells me that the coupling winding on the oscillator coil is open circuit. I decided to strip down the coil assembly, but the faulty winding was buried under wax. I made my own coupling coil of 4 turns and fitted it to the assembly, it works perfectly!
I finished by aligning the RF and IF stages as best I could.
Now I have a wonderful, fully restored Eddystone S750 in true BBC Repair Shop manner!
Here I am operating the Bolton Wireless Club station G8WY for the 80m Club Contest earlier this week. Bill G4CFP is logging the contacts on the computer. Using a Yaesu FT991 and 80m Dipole.
Brings back lots of memories with the G8WY callsign. Originally from the 1920’s, It was reborn back in 1972 when the Bolton and District Amateur Radio Society took it over for the club callsign. When the club folded the callsign was never renewed. It was recently taken over by the Bolton Wireless Club and is used for contests and special event stations just like it was in the old days.
Great to be able to use Golf Eight Whisky Yankee again!
Another addition to my uBITX project is a variable audio bandpass filter that I built from a constructional article by Eric GW8LJJ (Practical Wireless, May 2018).
The uBITX is a wonderful all band transceiver, but it has no filtering like the popular DNR, DNF and DBF filters that are found in commercial transceivers. To get around this a simple audio low pass and high pass filter connected in the audio output would make a big difference in reducing noise and separating CW stations on the bands. This design uses a very effective variable ‘brick wall filter’ The low pass filter is very sharp which is variable between 200Hz – 4Mhz.
On the back is a power socket, audio input / audio output and speaker connections. At the front is power, high pass filter and low pass filter controls.
Results with the uBITX are excellent, I can now filter out most of the background noise and separate stations, particularly CW stations, easily and effectively by adjusting the brick wall LPF. The HPF is less effective, but this only works between 40Hz – 200Hz, which is designed to filter out hums and other low frequency noise.
I decided to build the filter in an external box so that I can use it with other receivers, but this could easily be integrated into a uBITX itself.
I am really enjoying this renovation bug! I have already renovated two of my favourite receivers from the past, the HRO receiver and R1155 receiver. Both are working well and I am quite proud to have these old classics back to life again. My next project takes me back to 1971 when I bought a Hallicrafters SX24 receiver to replace my old R109A receiver. The Hallicrafters covered 1.8 – 30Mhz, my first all receiver. I kept this receiver until 1980 when I gave it away to a friend. I had moved on to buying a Yaesu FT101E at that time.
The Hallicrafters SX24 receiver in my shack in 1978
The Hallicrafters SX24 was a great receiver at the time and I always regretted getting rid of it. I wondered if I could get hold of one these again and renovate it like the one that I had before. Unfortunately, SX24 receivers are few and far between, I never see them on eBay apart from some in America. When I mentioned on Facebook that I was after getting hold of a Hallicrafters receiver, I was offered a Hallicrafters S20R receiver that needed some TLC and renovation. As the S20R is very similar to the SX24 apart from the S Meter and crystal filter and the circuit is virtually the same, I took the challenge.
The Hallicrafters S20R receiver before renovation.
The S20R receiver is working, but needs a lot of work, particularly changing all the capacitors and resistors underneath, this is something that I did with the SX24 many years ago, so I am quite familiar with the circuit and workings of this receiver. The dials on the S20R are very yellow with age and the Perspex windows are warped. All the switches are original and made from wood and need replacing. The chassis is mucky with some rust, but just needs a good cleaning with wire wool or emery cloth. The speaker is original and the cone has been repaired a few times, but it still works after 80 years!
The Hallicrafters S20R stripped down.
I remember spending a lot of time under the chassis of the SX24, I almost know by heart what all the trimmers do in the RF unit, alignment was fairly straight forward. I also remember that the mains transformer burned up one Sunday afternoon and had to be replaced. There were no fuses fitted then, with the S20R I will make sure that fuses are fitted.
I started to replace the components step by step. First replacing the smoothing capacitors and then moving on to different sections of the circuit. I tested the receiver after replacing each section so that I had not made any mistakes.
Underside and above after renovation. The old bulbs have been replaced with banks of LEDs, this makes the dials much brighter than the bulbs.
The case needed some TLC, I managed to mix some enamel model paint to match the colour of the case and touch up the scratches and parts where the paint had worn away. I used T-Cut Turtle Wax to renovate the colour and gloss of the paintwork without removing the decals on the front panel. I also made a decision to change the colour scheme of the Hallicrafters S20R to look like my SX24 by painting the main dial and speaker grill black. I also added a black fabric speaker fret on the front of the speaker. I replaced the dial windows with acetate that I designed on the computer to be identical to the originals. Unfortunately, apart from cleaning I could not do very much with the discoloured yellow dials, but they look much better with the clear acetate windows. I will add the aluminium side trims later, these will be painted black to match the rest of the case.
The renovated Hallicrafters S20R receiver with an external S Meter fitted. This looks and feels very much like my old Hallicrafters SX24 receiver!
The uBITX is an all band HF Transceiver kit made in India. It will produce about 12 watts output on the lower bands and drops off a bit on the higher bands.
I bought the uBITX Transceiver kit back in May, but until now I have not had time to build it up. I also bought a ready made case for the transceiver to make it easier build without having to find a suitable enclosure and drill all the holes.
The main board comes already built up and tested. It comes with a digital display and all controlled by an Arduino (called a Raduino) this can be updated by changing the firmware. Updating the firmware is quite straightforward once you have found the latest software. There is an immense amount of information on the internet about the uBITX, so before building I started my learning curve by finding the relevant information. I then saved links to it all the important things on my computer.
A word of warning…don’t be put off by the amount of information out there as a becomes very confusing and turns into a jungle. Just take one step at a time!
I started by building the small PCB that comes with the case, this houses the front panel sockets. (PTT Mic, Phones and Key) It is important that you follow the instructions as you have to add a 4.7k resistor on the board to make it work. I decided to solder in the connecting leads as this seemed the easiest method.
Next, I mounted the PCB to the front panel and screwed the main board into the case. There is another small PCB (again, this came with the case) that fits on the rear panel. This is for extra Jack connections, USB and Digital.
Finally, I wired up the supply, switch and fuse. An SO239 connector provides the aerial.
After completing the building I tested the receiver which works very well on all bands. I did need to set up the BFO frequency to make sure that USB and LSB sounded correct. This is explained in the instructions. The receiver is very sensitive and quiet as it does not need an RF Amp stage.
To test the transmitter, I used a dummy load and measured the output. I was getting 12 watts on 40m and 80m with a CW output, on 15m and 10m the output had dropped to about 5 watts. When I used SSB I found that the audio was a little low for my voice with the CB type microphone that I was using. There is no gain control on the board, so I built a small microphone amplifier with a gain control. This solved the problem.
The uBITX works fine at it’s basic level, now its time to start adding on to the basic uBITX. The first involves updating the firmware to make the transverter more user friendly, it gives more functions on the display. The firmware is supplied by KD8CEC and instructions are provided on his website http://www.hamskey.com.
One major problem with the uBITX is the lack of AGC. As there is no RF Stage it is difficult to add a normal AGC circuit. After doing some more research I found several circuits that had been tried with the UBITX, most of them audio derived AGC. I found a nice simple circuit by VK3YE that was quite novel, it samples the audio input from the volume control and drives an LED. The light from the LED is used to operate an LDR (Light Dependent Resistor) which is strapped across the volume control. It is very simple, but very effective. The sensitivity of the AGC can be adjusted. I built a printed circuit board for the circuit and can switch the AGC in and out by having a push / pull switch on the volume control.
Now we have the AGC working I next looked at the S Meter. There is provision for an S Meter on the display, but first you have to build a small circuit and update the Firmware. Again, I found a simple, but effective add-on circuit. You can find all the details here: http://www.hamskey.com/2018/06/creating-simple-s-meter-sensor-for.html
Finally, I added a very simple RF sensor to drive an LED on the front panel.
The uBITX with added S Meter circuit (black tape) AGC circuit, Mic Amp and RF sensor (bottom right)
I am really impressed with this little transceiver, it forms the basis of something much bigger by adding a NEXTION Display and a linear amplifier to give more output on the HF bands. The uBITX can also be CAT Controlled and ideal for use with FT8 and other digital modes.
Latest News on the uBITX project:
My next step with the project was to add a Nextion Display. I ordered a 2.8″ Enhanced Nextion Display from ebay, which is a genuine English version. It cost a bit more than the Chinese version, and came from a UK supplier. I was a little bit apprehensive about starting this modification as it involves updating the firmware again as well as adding the software for the Nextion itself. However, this turned out to be quite easy once you get your head around downloading the latest versions of the software. You need a micro SD card for the Nextion Software, which you plug into the card holder. There is only 4 simple connections to replace the original LCD display. I followed the instructions carefully and switched on the uBITX.
Wow! What an improvement…the uBITX is starting to look more like an Icom 7300!
This is definitely a ‘must do’ modification for the uBITX, the touch screen is easy to use and it is great to have a full colour screen. All the instructions needed for the modification can be found here: http://www.hamskey.com/2018/06/ubitx-with-nextion-lcd-cec-firmware.html