Racal Receiver RA117

2008-08-14T21:13:00.000+10:00

Edited various posts to include stage circuit diagrams.

2008-08-13T11:36:00.002+10:00

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.

2008-08-11T21:21:00.002+10:00

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.

2008-01-03T19:56:00.000+10:00

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...

2007-11-28T20:53:00.000+10:00

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.

2007-11-28T17:18:00.000+10:00

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.

2007-11-25T21:11:00.000+10:00

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.

2007-11-25T21:03:00.000+10:00

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.

2007-11-24T22:24:00.001+10:00

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.

2007-11-24T22:18:00.004+10:00

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.

2007-11-22T21:59:00.000+10:00

At least while doing the RA218 I have had the RA117 on test listening to MW BC stations. So far it's worked fine. The front end is now done and ready to go back in. I've just realised I forgot to photo the inside before I put the screen back on. Oh well, its only about 10 countersunk screws to remove so I'll do it tomorrow. I think before I re-install the front end, (after I have bench tested the 1st VFO) I'll take off the second VFO and try and get the calibration right. I also have a better quality film scale which I'll put on. The existing one is losing paintwork in places.

2007-11-22T21:46:00.000+10:00

Been side tracked the last few weeks with another piece of Racal gear. I bought an RA218 ISB adapter and have been cleaning it up. It was filthy dirty and smelly on arrival. So I've cleaned off all the gunk as far as possible. Also took of the front panel and gave it and the knobs a clean and polish. It worked OK as received, but checking resistors showed the typical 'gone miles high' behaviour. So I've been through and replaced them all, as well as all paper & ceramic capacitors and most of the electrolytics. It does a nice job of resolving ssb, the trouble is, it was meant to feed a teletype, so its high impedance headphone output only. I remaining niggle is the usb crystal is reluctant to start, unless a wire connecting it to the sideband switch is given a sharp tap. I think its the crystal holder as the pin can be wiggled up and down. But it's typically Racal in that getting the holder out means removing the front panel, the whole of the crystal oven and numerous soldered joints.

Here are some photos of the adapater.

2007-11-04T17:13:00.001+10:00

The next job, and the last major module is the front end: rf amp, 1st mixer and 1st VFO. Here are the pictures of this module as removed. It was the worst in terms of corrosion and dirt. All the screws and many of the nuts were very rusty, and the chassis itself was pretty dirty.

To the left is the 1st Mixer and 1st VFO, to the right the RF amp. The mixer and RF amp are linked by the the low pass filter at the bottom of the photo above. The complete circuit is shown below, including the front end low pass filter and attenuator I have also shown separately.

2007-11-04T17:09:00.001+10:00

Here are a couple of photos of the redone calibrator, top and bottom views.

2007-10-31T21:53:00.001+10:00

The rebuilt calibrator works fine. It was a bit tricky to get in - surprisingly as its just a push fit into an octal valve base, then is held in place with a couple of knurled screws. For some reason it just didn't want to fit that easily. Anyway, it's in and working, AND has a much nicer note that the one in my first RA117. Clearly that one needs a tune up.Having the calibrator in highlights how far off the VFO is in places. Not too bad in the middle of the scale, but way off at the ends. Anyway I'll finish off the front end before getting the second VFO out and getting it sorted. Some pictures of the completed calibrator will be shown below - I've yet to get them.

2007-10-31T21:49:00.001+10:00

The calibrator has now been finished. It got the usual complete rebuild with the unit reduced to a bare chassis. Here's the calibrator pre-restoration, plus the circuit.

2007-10-07T20:44:00.000+10:00

Having got the basic receiver apparently working, I though I should wire up the monitor switch. The original 2 pole 3 way had disappeared and been replaced with a 2 pole 6 way. I bought the appropriate switch and wired it up. After a few false starts I got it right and so can now read AF level, S meter and RF level (diode current). The snag was the S meter wasn't working. I checked the sensitivity of the receiver against the manual, using the RF level meter as specified. The results were pretty poor. After a lot of poking around I found the AGC was fully on, reducing the gain, and the RF/IF gain pot had no effect. It certainly was not changing the gain or affecting the S meter. Further diagnostics eventually revealed that the earth wire to the pot had broken. It was always a bit short so when I tugged on it to solder it back in place I must have snapped the wire inside the insulation. Second time on this receiver. I had had the pot out to open it up (it's wirewound) and clean it to get rid of the noise -successfully, I'm pleased to say.

Anyway fixing that brought the sensitivity right up to spec. So I have swapped the R237B LF adapter from my other RA117 to this one. The adapter raises the 10kc/s - 980 kc/s band upto 2 - 3 MHz. So now I can listen to medium wave BC stations while doing up the last module, the front end: RF amp, 1st mixer and 1st vfo.

Here's a photo of the receiver in its current state of renovation. A local station 4KQ on 612kc/s is pushing the S meter to 60dB over 9.

2007-09-27T21:40:00.000+10:00

Put the 1.7MHz box back in and connected everything up. Fed the 2-3Mhz sig gen into the rf socket and away it went. So that was the problem and I now have a basic fully working 2-3 MHz receiver. I'll have to try with the LF adapter to listen to medium wave broadcast band. While re-assembling everything I tightened up the speaker wires on the terminal block at the back. So far that seems to have got rid of the random crackling I was hearing before.

Checked the VFO span by fiddling with the tuning capacitor and the position of the film scale. It's not too bad now, but I will have to get the VFO off again and set up the variable capacitor again. I see from the book that the vanes should fully mesh at the LF end. They don't quite on this one at present.

2007-09-25T21:58:00.000+10:00

At this stage I could reassemble a lot of the receiver and test it as a basic 2-3MHz receiver. So the IF was refitted to the main chassis, the 1.7MHz box and 2nd VFO added and the whole lot fired up.
Injecting a 2-3MHz signal gave....nothing. Bypassing the 1.7MHz box and injecting a 100kHz signal into the IF was fine. Except for very noisy af and rf gain pots. They will have to be replaced. Also there is assorted occasional crackling which I can't pin down. There are no old leaky capacitors left. Maybe a noisy valve holder.
The fault must be in the 1.7MHz box. I checked it as per the book, which I should have done to start with. Injecting 3.6 - 4.6 MHz into the VFO amp showed that it was working ok. Injecting 1.6 MHz into the mixer and tuning up the IF transformers showed that it was also all ok, only very very slightly off peak. The 1.7 MHz oscillator was working, so only the last mixer was left.
Checking with a multimeter gave a weird result. There appeared to be no continuity between the screen potential divider and the screen (pin 6). It's shown here - all you can see is a little red loop, the rest is hidden.

The red wire looked to have decent soldered joints at both end!. A bit of waggling showed that the wire was broken inside the red plastic screen.
The offending wire is shown here. I had replaced this wire, so I must have broken the connection while stripping the insulation from one end.

Anyway, to remove it and replace it required removal of the power resistor, a decoupling capacitor and the central dividing screen (not shown in the photo above. I'll report back on whether that was the only problem or not.

2007-09-25T21:51:00.000+10:00

I haven't been inactive, just not updated the blog. I have finished the harmonic generation stage, and tuned the 1 MHz oscillator up to almost spot on frequency. Here is the complete stage. The 1 MHz oscillator and harmonic generator is at left, the low pass filter along the top and the harmonic mixer and 37.5MHz amp at right. You can't really see it but I replaced all the ceramic 10pF capacitors on the low pass filter with new silver micas. The only component not replaced was the R18/L20 combination at right.

2007-08-15T16:05:00.000+10:00

And here is the low pass filter which allows harmonics less than 30 MHz to pass through to the harmonic mixer. There are a couple of termination resistors, 330 and 470 ohms. The 330 had changed to 480 and the 470 to 730 ohms. You can see the replacement 330 in place. I will also check the capacitors, they are nominally 10pF. The small trimmer equalises the amplitude of the 28 & 29 Mhz harmonics during alignment.

2007-08-15T16:00:00.000+10:00

The harmonic mixer and 2 stage 37.5 MHz amplifier is done. I cleaned the rust off the UNF screws and re-used them. Underneath the tagboard (on the left) is a small piece of insulating card, which was falling to pieces. I replaced that with some thin card I had to hand. All these main chassis tag boards seem to have cards under and all need replacing. Anyway, here is the redone stage.

2007-08-10T21:26:00.000+10:00

Here is the tagboard after it has been completely updated. The only original component is the coil wound on a 470 ohm resistor which is the anode load for the 1st VFO.
I have now removed all the othe components in the compartment - valve bases, coils etc, ready for the rebuild. What I need are UNF screws, the old ones are all rusty. The OOO symbol I have seen on many bits eg the back of tagboards, bits of other hardware etc means UNF not BA screws should be used. They look similar but aren't interchangeable.

Here is the rebuilt 37.5MHz amp and second mixer in place.

2007-08-08T22:57:00.000+10:00

Still have to get a photo of the re-done 37.5MHz amp & 2nd mixer. Meanwhile it's on with the harmonic mixer and 37.5Mhz amps. Here is the complete 1 MHz oscillator, low pass filter, harmonic mixer and amplifiers in place. Then a picture of just the harmonic mixer and amplifiers in situ. Finally the tag board after removal, I had to remove a couple of components to get at the wires attached to the pins.

2007-08-06T19:46:00.000+10:00

For some reason I have now got stuck into the 37.5 MHz amp and 2nd mixer stage. As usual everything needed doing. Here is the circuit of this stage.

The mixer tuned circuits are in a small box on top of the chassis with a couple of wires threaded through grommets in the main chassis. Unsoldering the wires below and undoing the screws allowed the box to be pulled out. The same screws hold the tagboard in place, so removing the wires to the valve base allows the board to be removed.

Here is the little tuned circuit chassis, and a view of everything below chassis in situ.

2007-07-28T17:31:00.000+10:00

The IF strip connects in here. The original 1µF capacitor at left was just waggling loose in the joint on the earthy end! This is the AGC long time constant capacitor. The RF choke at right supplies HT to the 1.7 MHz box I rebuilt earlier. It had come free, so no HT was getting to this stage. No wonder the receiver wasn't working. Replaced all other capacitors, the 0.01 µF audio out at left, and the 0.1 µF BFO HT decoupling at right, along with 1.7 MHz box heater decoupling (0.001 µF). The 100k at extreme right will also need replacing, it is in the AGC line. Can't get hold of 100k resistors at present.

2007-07-28T17:25:00.000+10:00

The rebuilt PSU is shown below. I still have to complete the audio amp at right, its missing a few resistors and an 8 µF electrolytic.

The new 2 x 32 µF electrolytic was shorter and fatter than the original and did not fit in the mounting bracket. I have just glued it to the chassis wall with hot melt glue.

2007-07-28T17:16:00.001+10:00

The PSU on the main chassis was next, it was in a pretty tatty state, with dry joints, decayed components and cracked and brittle insulation where the wires have got hot. See the photos below.

The diodes were replaced, along with the power resistors and the electrolytics. The power resistors were replaced with 10W metal clad units which I have bolted to the chassis wall. A lot of the wiring was redone. At the same time the link on the Function switch that was putting the receiver on when the switch was in Standby was removed.

The audio stage is also in this compartment, here is the circuit diagram.

2007-06-25T20:40:00.000+10:00

Here is the underside of the VFO after rebuilding. I am still having trouble with the calibration. I cannot get the 1000kHz span within the span of the variable capacitor. Possibly the 10pf capacitor in the grid connection has changed in value - I used the original component and cannot remember if I measured it. The variable capacitor is set up correctly, at the 1000kc/s end there is still a bit of overlap of the plates, as per the RA17L book. This is a different VFO but the way the tuning drive reaches the end stop with the plates in this position, suggests the same approach was adopted in the RA117.

2007-06-24T20:28:00.000+10:00

Rebuilding the VFO didn't take too long - I still have to photo it though. I replaced the film scale, which turned out to be quite easy, although I still need to fiddle with it a bit. Fired the VFO up to find it was 1 MHz too high! As I hadn't changed any frequency determining components, it had to be one of the capacitors in parallel with the trimmer and the main tuning capacitor. Removed both, 15pF and 33pF according to the circuit. The 15pF was ok, but the 33pF (ringed in red on the photo) read 6pF! Replaced both and straight away the frquency came in range (3.6 - 4. MHz). Can't yet get it to scan correctly across the range yet. It's something to do with the position of the film scale and the amount wound on the spools at either end. Ok at 4.6 (0 kHz, but at 1000 kHz reads about 50 kHz off.

2007-06-23T12:32:00.000+10:00

Next job is the second VFO. Here are some pictures. I have removed the film scale for cleaning as it was pretty dirty. The spools were stiff and the guide roller was completely seized. Got them going freely again with some oil. The main tuning drive will have to wait until I have put the film scale back on. The VFO components were all past it, so it's strip down and rebuild as usual.

2007-06-23T12:22:00.000+10:00

I haven't made a post for a while, but I have been busy. The IF strip has been completely rebuilt, after taking everything off back to a bare chassis. The result is shown below. I have re-aligned it on the bench using an HP (Agilent) function generator to provide the 100 kc/s signal. It's a really nice unit for aligning the crystal filter as you can set the frequency to the last c/s if need be. The only trouble is the minimum output is 36mV RMS. Had to run it through my switched attenuator. Anyway, the IF strip is all aligned as per the RACAL handbook and seems to work fine.

Also did the 1.7MHz stage shown earlier. That gave me some strife as the 1.7MHz oscillator was reluctant to start every time. Eventually I found the problem (I hope) - an intermittent short between the 100K resistor to the metal plate at bottom right of the picture. RACAL put a sleeve over the wire and I didn't.

2007-05-05T19:04:00.001+10:00

Next off were the crystal and LC filters. These are in separate boxes, and their removal from the IF chassis allows it to be cleaned up nicely. There was some liquid from somewhere under the boxes, not sure if it was damp or the residue of switch cleaner I had been using. Also removed the associated larger tagboard. All these bits and the more empty IF chassis are shown here. It's surprising how heavy these filter boxes are. I also took out the shaft with the contrate gears used to switch selectivity - another very heavy item. With that lot off it is much easier to clean up the accumulated dirt.
The LC & crystal filter circuits are also shown below.

2007-05-05T18:57:00.000+10:00

Other bits come off the IF strip quite easily, next off was the IF output stage - just a small tagboard and an IF transformer, seen here. The 4.7k had reached 5.2k so was ripe for replacement - I don't want to have to get in again. Also replaced the 0.01 µF capacitor, plus, as usual, all components on the tagboard.

2007-05-04T19:13:00.000+10:00

Here are some pictures of the intestines of the BFO. You can see the 'trimmer in acetate case'. Racal receivers use a fair number of these and the case certainly keeps the dirt out. The case has been known to come loose and rattle around inside the receiver when you up end it.
I have stripped it completely down, cleaned the chassis (with Jiff and water), and the slow motion drive and tagboard. The resistors had all gone high and the capacitors looked pretty poor. I measured the silver micas and one was over spec, the other (39pf on top of the coil) was close, so I left it in place. Replaced everything else with brand new components. Tested on the bench on completion and it works fine.

2007-05-02T18:41:00.001+10:00

Various large sub-assemblies come off the IF strip. One of the easiest is the BFO. It was pretty dirty on the outside, so I pulled it off, and it too will have to have a complete rebuild. Only a single valve stage so it shouldn't take too long. I have a spare in much better condition in terms of cleanliness, but it still has old components. I should have rebuilt it ages ago to be ready as a drop in replacement. Anyway, here is the one that came out and its circuit:

2007-05-02T16:49:00.001+10:00

Next job was to pull out the IF strip. I had already taken off the front panel to clean it. That involved removing the side plates, also a necessary step in getting the IF strip out. Unsoldered the wires as per the book, undid the six screws and out it came, as seen here. The complete IF strip circuit is also shown, although the crystal and LC filters are just block diagrams.

2007-05-02T16:37:00.000+10:00

Finished rebuilding the 1.7MHz oscillator etc box today. They won't all be this quick, a few weeks long service leave helps. All components were replaced with brand new ones, with the exception of a couple of silver mica capacitors which measured pretty close to the required value. Here is a photograph of the tagboard prior to installation in the box and a photo of the completed box (minus the screen at this stage). Compare it with the original below. It was pretty tight around the 4th mixer stage, but it all went in. One of the biggest problems was valve pins and tagboard connectors not tinning properly, I'll have to find a better way of cleaning them off.

Now I can do a re-alignment on the bench, then pop it in my existing RA117 to check it out.

2007-04-29T19:51:00.000+10:00

2007-04-29T19:32:00.001+10:00

Decided to open up the 1.7 MHz stage. It's an easy one to get off the chassis. Here is a photograph of the top and bottom. Inside the components were in a very poor state, if you look at the enlarged photo (click on it). Resistors had gone very high (eg 15k -> 52k) and capacitors looked dead, with corroded leads and split casings. The trimmer on the 1.7MHz crystal was corroded and the vanes were bent, short circuiting it. No wonder the stage didn't work. It was also obvious that someone had been inside before, with some poorly soldered replacement components. As usual with Racal gear of this age, many of the joints were dry, the leads could just be unwound with a bit of a pull.

The date on the crystal is May 1963, so the receiver is around that age

Omly one thing to do: a complete strip down to a bare chassis and rebuild. At least it gives me a chance to produce some decent documentation.

Here's the circuit of just this stage.

2007-04-27T16:14:00.000+10:00

Here are a couple more photographs, of the top, and the underside. The underside is missing the separate screening cover over compartment 7 (top left) as well as the complete bottom cover. Both will have to be replaced to keep spurious responses down.

I tested all the valves on the AVO Valve Characteristic Meter Mk2, they seemed to be largely ok, with no major faults. Powered the receiver up using a variac, starting at very low AC volts. Wound it slowly up to 240v with no obvious fires or explosions. Heater voltage ok. Sound from the speaker, even with the function switch in Standby - that's wrong.

1 MHz oscillator ok and very close to correct. 1.7 Mhz oscillator appears dead, waggled crystal, changed valve - no change.

2nd VFO OK 3.6 - 4.6 Mhz out ok, can't measure 1st VFO at 40 MHz+ but my counter is not very sensistive.

Removed the 1.7 MHz stage box - it's an easy one to get out, 2 wire in compartment 7 have to be unsoldered (HT & LT) and 3 bolts undone from above chassis. Unscrewed the bottome screen and looked inside - full of dead looking components!

2007-04-27T16:10:00.000+10:00

Above is a front view of the RA117 receiver.

2007-04-27T12:18:00.000+10:00

Picked up the receiver today. It's definitely not as clean as my first one. A lot of the screws look rusty, and the front panel has a number of dirty (rust?) marks.

Anyway, here are some pictures.

2007-04-25T20:45:00.000+10:00

I meant to create a Blog for the first RA117 I bought, but thought about it too late.

I have just bought another (non-working!) on eBay and will be posting details of the restoration work here.

I'll pick it up tomorrow (Thursday 26 April 2007) and will add a few photos. One thing I do know is that it needs the bottom metal plate. Should be easy to knock one up in aluminium using my existing one as a template.