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Phil G4SPZ 16th Feb 2015 12:53 am

Trio 9R-59DS communications receiver (1970)
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I was given this early 1970s valved communications receiver by my very good and generous friend Phil Cadman G4JCP, who had owned it from new, but as the set had spent the last 25 years unused in his loft he felt it needed a bit of TLC and a new home. This type of set is a bit outside my normal ‘comfort zone’ when dealing with vintage valve radios, but Phil twisted my arm and I have spent the past week working on it. It had several faults including a couple I had not encountered before, so I thought I’d share the story with you.

The circuit diagram and operating manual are freely available on the internet, and show a single-conversion four-band superhet with two mechanical filters and one IFT in the IF stage, and a product detector for SSB and CW reception. The previous owner had added the optional 150 volt voltage stabilizer valve controlling the HT supply voltage to the local oscillator and BFO, together with the built-in valved crystal calibrator. This was fitted with a 1.0000MHz crystal, and after confirming with a DFM that this was running at exactly the right frequency, it proved useful later during the alignment process.

The initial obvious fault was an incredibly noisy volume control due to DC passing through the potentiomenter. This was quickly cured by replacing this set’s equivalent of ‘that’ capacitor, C32 (0.01uF) after which it worked quite well on AM. However, the SSB/CW function would work sometimes and not at others, and at this point began the search for what turned out to be two, separate, intermittent faults in the product detector and BFO stages.

Voltage checks around the BFO (V7a) proved that the BFO was oscillating, so I checked and/or replaced a number of components in the product detector stage. Each time, the product detector worked fine, only to fail again some time later. Each time, I checked to see that the BFO was oscillating, and traced the signal through to the third grid of the 6BE6 product detector. Sometimes the 6BE6 was mixing, and sometimes it wasn’t. A replacement valve provided no lasting cure, and after replacing several likely suspect components, I concluded that the gain of the stage was marginal. In the end, the culprit turned out to be C27 (0.01uF) which decouples the 6BE6’s cathode resistor.

My delight was short-lived however, because after a couple of hours’ listening the stage again failed. If I had any remaining hair, I would have torn it out... this time, though, the fault was in the BFO stage, which appeared to stop and start oscillating at random, as if it had a mind of its own. After replacing the 6AQ8 BFO valve and exhaustively checking or replacing every associated component, the only thing left was the BFO’s tuned circuit. I removed the screening can - not an easy task, involving plenty of de-soldering braid on the underside of the PCB - to find a 1,000pF polystyrene capacitor lurking within. I have a deep suspicion of this type of capacitor, and sure enough, when it had been replaced and the stage realigned, the BFO remained perfectly stable. Two separate intermittent faults in two adjacent stages but producing the same intermittent fault symptoms must be pretty unusual, but Sod’s Law always seems to apply to me!

I then started the alignment process. The IF stage was 2kHz off its nominal 455kHz, but realignment was straightforward. It then became apparent that I could align the local oscillator to give correct dial readings at the bottom of each band, but it was impossible to achieve correct alignment at the top. After some time spent scratching my head, it dawned on me that the bandspread variable capacitor should be set to minimum capacitance before commencing alignment. The service manual doesn’t mention this. Perhaps the manufacturers only expected intelligent engineers to align this set! Once this was done, bands A (550kHz-1,600kHz) and B (1.6MHz-4.8MHz) were aligned quickly.

It then became clear that I had major problems on the two higher bands. On band C (4.8-14.5MHz) the local oscillator frequency was highly unstable, and would wobble if I so much as looked at it! Touching any part of the chassis or flexing the metalwork would send the LO off into a spin. Remarkably, the manufacturers had used ordinary flexible stranded hook-up wire throughout the VFO and coil pack, including a lengthy run of wire between the local oscillator section of the band switch and the main tuning capacitor. I replaced this wire with a length of solid wire, and this brought about considerable improvement, but after much time spent carefully trying to find the cause of the remaining instability, it eventually transpired to be CT7. This is a 0-20pF concentric trimmer of a type I’d not seen before, incorporating a screw-adjustable slug running up and down inside a plastic tube, the bottom part of which was surrounded by a metal sleeve. Contact between slug and earth was via contact between the threaded operating rod and the rather crude ‘nut’ formed by the tinplate top of the capacitor. After a struggle to extract the trimmer, it appeared that the heat from the original soldering during manufacture had melted the plastic tube, and also the tinplate top had split at one side, allowing the threaded rod to wobble about. I measured the maximum capacitance at roughly 20pF. I had nothing like this in stock, but I did have a 30pF Philips beehive trimmer which seemed to fit the bill, and with a bit of ingenuity this was soldered solidly to the trimmer mounting bracket. After connecting up I found that the instability had vanished, and I was able to obtain smooth adjustment of the trimmer at the upper end of band C.

The next problem was that the local oscillator stopped on band C below about 6MHz, and after trying to align band D I found that the local oscillator was also running out of steam on that band above about 16MHz. On the two higher bands, the local oscillator amplitude was way below what it was on the lower two bands. Yet again, I exhaustively checked and/or replaced all likely suspect components around the coil pack and VFO, but to no avail. I checked the resistances across all the band switch contacts, but these proved perfect. It appeared that the upper two bands’ VFO coils had somehow lost some of their “Q”, but all soldered terminations were sound and the coil resistances were as expected. Internet research suggested that this fault could be caused by a low-emission local oscillator valve (V3, 6AQ8/ECC85) but a brand-new, 100% perfect replacement valve had no effect.

At this point I sought the help of the Forum, and G6Tanuki came up with the suggestion that some Japanese manufacturers in the 1970s coated their coils with a type of wax, which degraded over the years and became lossy, reducing the coils’ Q. Having little to lose, I applied gentle heat from a hairdryer to soften the waxy coating, and removed as much of it as possible using a cotton bud - aptly named a “Q-tip” - and I found that the coating looked like, behaved like and smelled like candle wax. Sure enough, the problem was cured. I now had full coverage of both bands C and D, and the VFO amplitude increased to something more like normal.

As I was quietly congratulating myself, all signals slowly died away. The heater of V2 (mixer, 6BE6) had failed due to air ingress into the valve, presumably as the result of localised overheating near the pins caused by the hairdryer. A replacement valve restored normal operation, and after a final realignment of bands C and D and a prolonged soak test, the set was reassembled and declared fully fit for duty in the G4SPZ radio shack.

There is quite a lot of criticism of the Trio 9R-59DS in various Forums on the internet, this one included. Some of this is quite justifiable; the physical construction of the chassis is more akin to a domestic superhet than to a genuine communications receiver, and some frequency drift is noticeable on the higher bands. Its image rejection performance is also likely to be questionable. That said, the set is very sensitive, highly selective (particularly on medium waves, which apparently gave this set a good reputation amongst medium wave DXers) and its long-term frequency stability is more than adequate for most listening purposes. It is also relatively easy to work on. I am very pleased to have this set as an addition to the shack.


G4XWDJim 16th Feb 2015 8:29 am

Re: Trio 9R-59DS communications receiver (1970)
Good write up Phil as always and well done.


David G4EBT 16th Feb 2015 11:00 am

Re: Trio 9R-59DS communications receiver (1970)
I look upon the 9R59DS with fond affection. It was my first short-wave receiver, bought pristine but second-hand in 1971, and luckily, it came with the now rare matching loudspeaker as there isn't a built in speaker - just a phone socket.

Most of the limitations were well known back then, and there was a series of modifications in the much lamented Radio Constructor Magazine to improve the performance and to add features. As to poor image rejection, it isn't of course unique to the 9R59DS - it's something that all single superhets have in common on the higher frequencies. It does at least have bandspread.

Some of the mods included fitting a crystal calibrator and voltage stabiliser, fitting a smoothing choke and re-positioning the OPT away from the mains transformer, to reduce hum levels, improving the IF stage, and so on. I did most of the mods on mine. They're ideal to work on as they're so large, which means that the internal layout of components isn't cramped.Inevitable that as they approach their 50th birthday, the usual problems are starting to develop, and I dare say that of those that do turn up from time to time, they'll often have been 'got at'.

Beauty is in the eye of the beholder, but I always liked the appearance of the set, and still do. There was one at the NVCF last May which was unmarked and un-tampered with, compete with speaker, at a giveaway price. I was sorely tempted and nostalgia almost overcame common sense but I'm in 'de-cluttering mode', so I passed on it. It wasn't there long.

Enjoy the set Phil.

raditechman 16th Feb 2015 11:22 am

Re: Trio 9R-59DS communications receiver (1970)
An interesting read, thank you Phil.

Like David I too have an affection for these receivers, as I bought one new around 1968 as my first "amateur" receiver. It was the best I could afford back then. I fitted the OA2 stabiliser, although the set still drifted a bit until warmed up,as most listening for me then was on 160m Top Band AM the drift was tolerable.

Nice to know your set has a good home and is has been well cared for.


terrybull 16th Feb 2015 2:30 pm

Re: Trio 9R-59DS communications receiver (1970)
I had one of these too. I like the appearance and it was a decent set to use. I lost one band and traced the fault to a loose wire on one of the tuning coils. It did drift badly but was predictable so you could 'chase' the signals. Kept you involved and awake when listening. Nice write up Phil.

Aub 16th Feb 2015 8:40 pm

Re: Trio 9R-59DS communications receiver (1970)
Very well done and thanks for posting this. A very enjoyable read.


Aub, G4KQL

Andrewausfa 16th Feb 2015 9:25 pm

Re: Trio 9R-59DS communications receiver (1970)
Good write up Phil. I've had a weather eye out, just one eye mind you, for a while for one of these in case one popped up at a rally or something.


Radio Wrangler 16th Feb 2015 9:41 pm

Re: Trio 9R-59DS communications receiver (1970)
They were cheap and cheerful, so there should be plenty around. The main limit on their sales was that there were also some good ex-government receivers available in the same era in competition for the SWL's pound.

Now is a good time for getting an HF receiver going. The bands are open right up to 10m in the mornings.


Phil G4SPZ 16th Feb 2015 10:55 pm

Re: Trio 9R-59DS communications receiver (1970)
Thank you all very much for your kind comments. Sorting out this radio has actually re-kindled some of my old interest in short wave listening, away from the amateur bands!

Oh, and I'm pretty confident that the intermittent faults have hopefully gone for good, too. I've had this set running for many hours now, and apart from the drift - which incidentally seems to be related to mains voltage as much as anything - the radio has performed perfectly. But please don't tell it I said so...:devil:

David G4EBT 17th Feb 2015 10:03 am

Re: Trio 9R-59DS communications receiver (1970)
I’ve just looked at the manual and see that as I recalled, there is a valve socket present for the OA2 150 Volt stabiliser valve, so all that is needed is to plug one in.

The manual also explains how to build in a crystal calibrator for which holes are already punched in the chassis to accept the crystal and valve sockets. It suggests using a 3.5 MHz crystal if the main interest is in the amateur bands, to mark the band edges of 3.5, 7.00, 14 & 28 MHz. Otherwise, a 1 MHz/100kHz crystal could be used. The manual explained that a spare switch on the RF Gain control could be used to switch the calibrator on and off. It provides a simple one transistor circuit for the calibrator. (Instead, I added a valve calibrator using a 6BA6 valve, as described in the Radio Constructor mods).

It seems rather odd that Trio made provision for these useful added features, yet didn’t install them at the factory for the minimal additional cost involved, which from a marketing point of view, would have enhanced the features and benefits of the receiver, but it must have been a very price sensitive market so they were clearly trying to keep the retail price down. I don't think any manufacturer these days would include in the user manual diagrams to show how you could hack the printed circuit board about, cutting through tracks to modify the receiver! (No disclaimer either). Simpler less litigious times, when if people did something daft or negligent, they'd accept personal responsibility for their mistakes - not shift the blame onto someone else.

It has a send/receive switch to switch off the HT when used with a transmitter, back in the days when it was commonplace to have a separate receiver and transmitter, which is a handy feature for anyone who might want to use the receiver in conjunction with say a home-brew QRP transmitter.

The original 13-page manual can be downloaded F.O.C from the ‘BAMA’ website (Boat Anchors Manual Archive) here:

The excellent Radio Constructor Magazine articles in Oct 1970 and in March/April 1971 by Martin Lindars covered extensive modifications which included such things as:

Improved power supply,
Fitting screen grid resistors,
Adding a tape recorder socket,
Separating the RF/IF gain controls,
Improved oscillator stability above 15 MHz,
Eradicating unwanted RF coupling along the heater line,
Fitting a double-tuned RF stage, voltage stabiliser & crystal calibrator,
A separate 6.3V supply for bandspread/bandset dial bulbs, to facilitate the fitting of an 'S' meter dial light,
Reducing mains hum (noticeable when using 'phones) by repositioning the OPT beneath the chassis away from the mains transformer,

Finally, full alignment.

Happy days!

Hope that’s of interest.

G6Tanuki 17th Feb 2015 10:04 am

Re: Trio 9R-59DS communications receiver (1970)
Nice one !! Good to hear you got to the bottom of the various issues: when you have several concurrent faults it can really tax your Sherlock Holmes skills!!

As has been mentioned, there's quite a bit of amateur activity on the upper HF bands [14-21-28] at the moment so if you can, sling up a dipole for your favourite band and see what you can hear.

turretslug 17th Feb 2015 8:48 pm

Re: Trio 9R-59DS communications receiver (1970)
:thumbsup: Good to hear that this has been a success after what must have been a demoralising chase in the BFO department- but conclusion makes putting to succesful use all the more satisfying! The forum certainly proved it's worth re. the Q-sapping wax, too- another one for the cranial file. One of the receivers I've been tempted to acquire on occasion if space/time/life permitted- it might be looked down on by some but, as RW highlights, the SWL/amateur scene was rather spoiled by the excellent professional/military receivers available at a fraction of their real cost. After all, a tuned RF and two IF stages make it a radio with intent.

I wonder if the mains-dependency component of the LO drift might be helped by adding the mixer screen-grid feed to the stabilised supply? Long ago, I found through tinkering that this could make a small but significant difference to oscillator stability- after all, changes in screen-grid voltage and effect on electron stream effectively look like a variation in capacitance on the output of the oscillator. It may be slight, but "slight" is still significant for SSB readability at HF. A quick bit of fag-packet maths suggests a 10k (miniscule wattage) feeding the existing 68k from the nominal 150V, rather than the 134V signal valve rail. The extra 1.6mA from this rail shouldn't shift the stabiliser operating window significantly.

Phil G4SPZ 17th Feb 2015 9:18 pm

Re: Trio 9R-59DS communications receiver (1970)
Thanks again chaps, some really interesting observations and suggestions there.

I'm disinclined to undertake the major mods that David so usefully listed, mainly because I do prefer originality and have been aiming to get this set running as it would have done when new. But having said that, in reality the drift is a bit of a pain, so I'd like to improve that aspect of its performance if possible. Turretslug's suggestion is one I'll definitely pursue, but I want to do a few tests regarding mains variation and frequency stability. I have a 160 VA constant voltage transformer so I'll try that out first. It seems to be the case that Trio were trying to appeal to the true well-established amateur radio spirit of home construction, and so they actively encouraged modification, which was perfectly acceptable at the time - once the radio was out of guarantee, of course! Not so nowadays with the usual 'no user-serviceable parts inside - opening case invalidates warranty' statements and three pages of Health and Safety warnings at the front of the handbook. With the passage of the years, however, I suspect many of us would now strive to preserve originality, rather than modify a vintage radio, even if a performance improvement resulted.

One interesting difference emerged between the original user manual that came with the set, and the copy I downloaded from the internet. The original paper copy (presumably earlier) manual includes a valved crystal calibrator, and this is the version of the circuit that the previous owner built into the set. The downloaded (later) manual substitutes a transistor circuit.

Notwithstanding the frequency drift, which as Terrybull so nicely put it "keeps you awake whilst listening", this receiver has been giving me some excellent CW and SSB signals on 40 metres all day, on a very modest random wire antenna. With a resonant antenna, properly matched, I'm sure it would perform even better.

Radio Wrangler 17th Feb 2015 10:57 pm

Re: Trio 9R-59DS communications receiver (1970)
We're in a different world than when the modifications were published for the 9R-59DS.

Back then a 9R-59DS was the best that many people could afford, and if they wanted anything better, they had to get out the soldering iron, drills and file. On 5 bob a week pocket money, I couldn't afford a 9R59DS to start with, so I followed the surplus route.

Nowadays, if you have a 9R59DS and hanker for a better receiver, you can probably afford one. What takes your fancy? An RA17, a Frog-7, an Eddystone? Drake? Collins? or stick with Trio and find a JR599?

I think the greatest value, now, of a 9R59DS is in keeping it original as an illustration of how things were. In days gone by it was different.


Phil G4SPZ 17th Feb 2015 11:36 pm

Re: Trio 9R-59DS communications receiver (1970)

Originally Posted by Radio Wrangler (Post 743864)
...What takes your fancy? An RA17...

Ah yes, the RA17. I was given one once, complete with the metal rack case. It weighed a ton and it worked very well but it virtually filled my shed. When it broke down I literally hadn't enough room to dismantle it to find the fault (nor probably the knowledge) so I swapped it for a far more useful DFM.

I agree with you David about keeping my example as original as possible.

I've since been playing around measuring drift and mains voltage to see if there is any correlation. The answer is yes - I can use my variac almost as a fine-tuning control - but I think it's more related to temperature than anything else. At switch-on, the drift is in one direction (LF) but after about 20 minutes, during which time it drifted down by 2kHz, the frequency settles down a lot. Until, that is, there's a slight change in room temperature or mains voltage, which sets it off again.

One question - is the main VFO valve V3 supposed to have a metal shield over it? The valve base has three springy metal fingers that grip the base of the valve, but my set has no shield. The picture in the service manual isn't very clear, but may show something covering the valve. If anyone can tell me, I'd be most grateful.

Hybrid tellies 18th Feb 2015 12:20 am

Re: Trio 9R-59DS communications receiver (1970)
That was some job. A very interesting read.

Phil G4SPZ 18th Feb 2015 9:11 am

Re: Trio 9R-59DS communications receiver (1970)
Thank you, Simon.


Originally Posted by Phil G4SPZ (Post 743868)
One question - is the main VFO valve V3 supposed to have a metal shield over it?

I can answer my own question: several picures, including an image here clearly show metal shields over not only the VFO valve but also the RF amplifier and BFO too. Now I wonder where they went?

turretslug 18th Feb 2015 2:36 pm

Re: Trio 9R-59DS communications receiver (1970)
I assume those shields are a springy scroll sort of construction that wraps snugly round the valve in question- I wonder if a bit of creativity with tin snips and food tins etc. would make a workable substitute?

As an aside, those pictures in the link seem to set a new reference level of gruesomeness in the "got at" stakes. I was feeling rather ill by time I'd got to the one with the bridge-too-far rectifiers, the extra (PCB-mount?) transformer secured by a tie-wrap and what appears to be a mains filter culled from an SMPSU, nicely insulated by a gash piece of cardboard! A feast of gaffer tape. I can well imagine that a single-ended audiophile amp with high-power triode and high-efficiency horn speaker would need an HT filter that included 2x 470uF smoothing but surely not a modest current HF radio? :shrug:

Phil G4SPZ 18th Feb 2015 5:57 pm

Re: Trio 9R-59DS communications receiver (1970)
If I had ever done work as untidily as that, I would certainly not have publicised it! Has the perpetrator no pride? I wonder what he does for a day job? Butcher, probably :laugh1:

G6Tanuki 18th Feb 2015 6:40 pm

Re: Trio 9R-59DS communications receiver (1970)

Originally Posted by Phil G4SPZ (Post 744020)
If I had ever done work as untidily as that

"put together by a thousand blind pigeons using an axe" as a work colleague would put it.

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