Edited various posts to include stage circuit diagrams.

I have started adding the various stage circuits to the appropriate parts of the rebuild description. I have just chopped the stages out of the complete diagram, in various parts if that was necessary, stitched them together and cleaned up the result in Photoshop. It makes it much easier to do a rebuild if you just have that stage's circuit to look at.

I have just had a coherent write up of this project published in the UK magazine 'Radio Bygones', No 114, July/August 2008. See my writing blog at:

www.peterholthamswriting.blogspot.com

A reader of RB has been kind enough to email electronic copies of some manuals for the RA117 (UK Electrical & Mechanical Regulations, E802 -E804) which provides some useful additional info.

I must get round to putting up all my cleaned up circuits for each here on this blog. I think there are one or two further back, but not the complete set.

Not much to report. I have been using the RA117 a lot now on my outdoor 40m dipole and it seems very good indeed. I am certain it's outperforming my first one.

The only things I have done is replace the built in speaker, the original one was completely shot, the paper cone had disintegrated. I picked up a 2nd hand one on Ebay for £2.50 in perfect condition. It's fitted now and works fine, except I never use the internal speaker!

Also found on Ebay a replacement for the one missing screening cover, the one over compartment 7, So I've fitted that and now need to cut a complete base cover out of 1mm aluminium.

Then I should really do the 2nd VFO calibration - a big job really as I will have to take off the front panel yet again and get the VFO out.

I've also modelled the 2-3 MHz filter using the capacitor values from the circuit diagram and adjusted the inductance values to get a good predicted response. What I should do is then take the filter off and measure the values and try and tune it up, as the response I measured was a long way off ideal.

Always lots to do...

Playing with the receiver again this evening. I still can't find the BBC on 9740, so I checked on other receivers. No sign, so there must be a frequency change or TX fault.
The RA117 seems very lively indeed. Tried it with my Elecraft signal source. This is just 3 spot frequencies in the 80, 40 & 20m amateur bands with an output of 50µv (the nominal S9 standard) or 1µv switchable. On all 3 the RA117 showed S9 plus about 5dB with 50µV and the 1 µV signal was plainly audible. Went inside and tried my other RA117, which I have done a lot less work on. Here the best I could get was just a shade over S5 on the 50µV signal, the 1µV was audible though. Clearly the two receivers are going to have to swap places for a while, while I do a retune of the old one.

Replaced the old film scale with a better quality second hand one. Then put the VFO back into the receiver. Connected everything up and then checked the calibration as per the book. I was finally able to get the 0 and 1000 kc/s positions ok, and the 100 and 200 looked ok against the internal calibrator, so I decided I couldn't wait any longer to try the whole receiver out. Connected an indoor dipole mounted in the shed roof, tuned to the BBC on 9740 and found nothing, but there were stations about. Tuned around abit and found the BBC rather weakly on 9760, so the calibration is out at that end of the band. Then I noticed the attenuator was still at maximum. Switched to zero attenuation and got the BBC at S9++, so the complete receiver is working fine (at least at that frequency).
Decided I had better check the VFO calibration, with the result shown below. Obviously I am going to have to tweak the variable capacitor somehow. The book talks gaily about this but offers no useful detail.

Also worked on the 2nd VFO. Undid the screws connecting the tuning drive to the tuning capacitor shaft. Then I could lever the tuning gear forward just enough to free the capacitor. Aligned the capacitor plates to be fully meshed - they could never get there before, pushed the tuning gear back and tightened up the fixing screws. Adjusted the film scale to be right at the end of its travel at the 1000khz end. The manual is a bit obscure here. The RA117 manual says make sure there is 7.5 inches from the cursor to the extreme end of the scale. There's just not that much length available unless they expect you to measure round the drive pulley and along the back of the scale. The RA17 book says 0.5 inches which makes much more sense. So worked with the RA17 instructions. I then fired the VFO up, tuned it to the 0 kHz end and adjusted the trimmer capacitor until I got 4.6MHz on the counter. Wound the dial to the other end of the scale and there was 3.6 MHz on the counter. So I finally have the full 1 MHz span with a bit extra at either end. Now all I have to see is whether the calibration is reasonableat each 100 kHz point. Will re-install the VFO to do that. But first I will install the better quality film scale.

Finally photographed the underside of the completed front end, here it is just prior to installation. A cover fits over the base before it is mounted on the main receiver chassis. The hardest part of remounting it was getting the rf feed coax through the grommet into the attenuator compartment. In the end I cut off the original tinned braid and centre as they were rather too big for the grommet. Fortunately, there was just enough coax left.

Bench tested the first VFO, seems to work fine and is reasonably stable considering it tunes 40 - 69MHz. Still have to photograph the renovated front end before installation.

While remounting the attenuator & low pass filter, I noticed I had forgotten to wire the AGC line from the IF strip to the front end. Its a short length of coax from R81A (1.5k) to a ceramic pillar next to the if strip which has R119, 100k on it. You can see the pillar and resistor at the left of the photo posted on 28 July 2007. At that point I hadn't replaced the 100k resistor. So made up a short piece of coax and completed the connection. I hadn't noticed, because with the front end out, and using the LF converter, the AGC is not required at that point.

Also noticed I hadn't fitted the last large bolt which helps hold the 2nd VFO from below, I just put the two top bolts back in. Anyway the 2nd VFO has to come out to fix the span, and allow the front end to be refitted. So, once again, the front panel is off ready to do that job. I hope I am on the home straight now.

Did up the front end attenuator and low pass filter today. Yet another low pass filter - 3 coils and capacitors in a pi arrangement. The 82pF capacitors were small dog bone ceramics in clear plastic sleeves. It was this type that was way out in the second VFO so I replaced them all with some new silver mica ones. Also replaced all the resistors (100 and 150 ohm) in the 4 position attenuator. Most were still within 10% but on the way to too high. Cleaned up all the switch contacts and replaced the whole thing back in the receiver. Here are some photos of the as found unit. I have also added the circuit.