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Old 17th Jun 2024, 12:19 am   #1
Etaoin Shrudlu
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Smile Trying to fix my father's Trio 9R-59.

Hi all,

My dad was a keen radio amateur in his youth (50s & 60s) and couldn't resist a Trio R9-59 shortwave receiver he recently stumbled upon at a jumble sale - especially since it was only a tenner. It doesn't work of course, and since I'm pretty good with electronics he's asked me to see if I can make it go again. It's a very cool looking unit, and externally in excellent condition, bar missing the main tuning knob - but the internal chassi had been drenched with... something... that had dried up and gone all crusty. There was also a spot of pretty bad rust in one place, which thankfully hadn't affected the nearby tube socket. After spending several hours carefully wiping it with bits of damp dishcloth and q-tips I've managed to clean it up pretty well. I got rid of most of the rust by rubbing the affected area with q-tips dipped in spirit vinegar, after which I neutralised the acid with bicarboante (which is also a good abrasive) and rinsed with water. A tiny bit of oil applied with a q-tip should stop the rust from coming back. I removed and managed to clean the tubes without losing any of the lettering (which I know very easily happens), and I sprayed the sockets, as well as the pots and rotary switch contacts, with a good quality oil-free contact cleaner.

The component side of the chassi was thankfully spared whatever distgusting liquid had been spilled inside, and looks to be 100% factory. There are no burned components or other obvious sings of trouble. I've identified four "Suzuki" paper in oil caps that will need replacing, and one electrolytic that might be. There's also a canned dual 40 uF cap on the power supply side. The rest of the caps seem to be ceramic or mica, so should be fine. I didn't trust that the central grounded pin on the three way lug strip that is riveted in the middle of the area affected by rust would still provide a good ground, so I soldered a piece of wire from it to a reliable ground point nearby. I made no other modifications.

After letting it dry overnight I reassembled the set and plugged it in via a lightbulb. Nothing dramatic happened when I switched it on; the scale lit up and I could hear a faint hiss & hum from the speaker, but there was no static and I could get no reception on any of the four bands. While I know my way around most kinds of electronics; power supplies, amplifiers, computers - and can design my own transitor and logic based circuits from scratch, I know basically *nothing* about radios, and even less about vacuum tubes - other than that they look pretty and run on dangerously high DC voltages. I managed to find a decent copy of the schematic, and a poorly scanned page from some kind of service manual which lists the voltages that should be present on the pins of each tube. I've converted the list to a spreadsheet and added my actual measured values to it, in the hope that someone here might have a suggestion as to what the fault might be (n.b. I have not measured V4 since it's not accessible from the bottom of the chassi). I've attached the list as an image since I couldn't see any way to create a table inline with my post - hopefully it's still readable.

I'm confused by the 6.3V AC (filament voltage?) not being on the pins listed for all but one of the tubes, but I'm pretty sure this is by design; I can see where the wiring switches pins after V6. If the filaments are between pins 3 & 4 and they run off AC switching pins won't matter but perhaps there's some radio reason for doing this that I don't understand (phase?). In any case I can clearly see all nine tubes glowing nicely when the set is on. Another thing that stands out is the low voltage seen on pin 1 of V2 & V3 - this should be negative 7.7 volts according to the list, but I'm measuring just -1.4V, and the voltage immediately starts to drop when under measurement. That can't be right.

What do you guys think, any suggestions?
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Old 17th Jun 2024, 7:54 am   #2
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Default Re: Trying to fix my father's Trio 9R-59.

That's a nice clean-up job.

I think you're OK with this set, but plenty of American radios and Heathkits were made with golden-coloured cadmium plating on steel chassis which could be unhealthy to use abrasives on.

The place with the negative DC voltage on it will be part of the AGC system. In general, the detector diodes used to demodulate AM signals are wired the way round which turns the carrier of the signal in the IF into a negative-going DC voltage. Demodulation would work just as well the other way, but the negative DC component is ideal to be applied as bias to the grids of the amplifying valves to reduce their gain progressively with larger input signals.

The input impedances of valve grids under normal linear operation are extremely high, and the time-constants needed for good AGC action are in the hundreds and thousands of milliseconds. With paper capacitors of typical values, there are some high value resistors in AGC circuits, and your voltmeter will load them significantly, and the capacitance will show the voltage drop over a noticeable amount of time. What you've seen here is perfectly normal.

Some 'communications' style receivers have RF gain controls to override the AGC and some designs need a negative voltage supply to achieve this. It's common to have a dropper resistor in the negative output of the HT power supply to chassis connection to drop several volts. So the negative end of the HT power supply becomes several volts more negative than chassis. As the HT current is dominated by the quiescent current set in the usually single-ended class A audio output stage, the negative voltage is predictable and stable enough.

The 9R-59 was sold as an entry level receiver for hobbyists. It's main competition were war surplus receivers in the 1960s. Most of these were higher quality and a bit better performance than the 9R-59 receiver, but the little Trio looked neat and a lot more presentable to parents. It uses two tuning capacitors. A main one to tune across larger ranges, and a fine tuning one called 'Bandspread' There are marks on the main dial. Tune onto one of these marks and then use the bandspread, whose dial is marked for the amateur bands of the day (there are more, now). For general tuning around outside the amateur bands, the bandspread dial has to be parked in the right position so that the frequency markings on the main dial are not offset.

As a beginner's set, it was designed to get someone going and interested, but they would relatively soon run into its limitations and start saving for something better.

The radio has provision for a voltage regulator tube to stabilise the HT supply to the two oscillator valves (the superhet LO in the front-end and the BFO for SSB and CW reception) These regulators were not fitted at the factory, but a hole was punched in the chassis to fit a valve holder and wire one in. You may just find the hole, or if you're lucky one mght already be fitted.

David
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Old 17th Jun 2024, 11:14 am   #3
Etaoin Shrudlu
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Default Re: Trying to fix my father's Trio 9R-59.

Quote:
Originally Posted by Radio Wrangler View Post
That's a nice clean-up job.
Thank you! It was a pretty disgusting job tbh. Not sure what was spilled on it, but it seemed to be some kind of foodstuff...

Quote:
Originally Posted by Radio Wrangler View Post
I think you're OK with this set, but plenty of American radios and Heathkits were made with golden-coloured cadmium plating on steel chassis which could be unhealthy to use abrasives on.
Crikey, that's good to know! I'll make sure not to drink the water next time

Quote:
Originally Posted by Radio Wrangler View Post
The place with the negative DC voltage on it will be part of the AGC system. In general, the detector diodes used to demodulate AM signals are wired the way round which turns the carrier of the signal in the IF into a negative-going DC voltage. Demodulation would work just as well the other way, but the negative DC component is ideal to be applied as bias to the grids of the amplifying valves to reduce their gain progressively with larger input signals.

The input impedances of valve grids under normal linear operation are extremely high, and the time-constants needed for good AGC action are in the hundreds and thousands of milliseconds. With paper capacitors of typical values, there are some high value resistors in AGC circuits, and your voltmeter will load them significantly, and the capacitance will show the voltage drop over a noticeable amount of time. What you've seen here is perfectly normal.
Thank you, that's a nice explanation! But my meter (Brymen BM357s) has a DC voltage input impedance of 10M?...

Quote:
Originally Posted by Radio Wrangler View Post
Some 'communications' style receivers have RF gain controls to override the AGC and some designs need a negative voltage supply to achieve this. It's common to have a dropper resistor in the negative output of the HT power supply to chassis connection to drop several volts. So the negative end of the HT power supply becomes several volts more negative than chassis. As the HT current is dominated by the quiescent current set in the usually single-ended class A audio output stage, the negative voltage is predictable and stable enough.
I guess this means earthing the chassis would be a bad idea?

Quote:
Originally Posted by Radio Wrangler View Post
As a beginner's set, it was designed to get someone going and interested, but they would relatively soon run into its limitations and start saving for something better.
I think the appeal of the Trio lies more in its appearance than its functionality, being as it is of a similar vintage to himself. He's also got a more modern Lowe HF-225 receiver that I got him some years ago, which is what he uses to listen with. He lives close to a small airport and former airforce base that still sees some use so there's plenty of local traffic. The Lowe is a great little radio, though it's missing the optional D/DU-225 FM/AMS detector board - been trying to pick one up for him but they're both rare and expensive! Saying that, the Lowe is a lot less fun to look at, and I think he struggles to make the most of the digital controls... For these reasons, and despite its pedestrian performance, I still think it's worth spending a little time (and £££) to get the Trio back in action?

Quote:
Originally Posted by Radio Wrangler View Post
The radio has provision for a voltage regulator tube to stabilise the HT supply to the two oscillator valves (the superhet LO in the front-end and the BFO for SSB and CW reception) These regulators were not fitted at the factory, but a hole was punched in the chassis to fit a valve holder and wire one in. You may just find the hole, or if you're lucky one mght already be fitted.
Interesting! There is no voltage regulator tube fitted, only the nine original tubes, and I cannot see any punched hole for a tube socket - though there is one that appears to be for a small switch, near to the mains transformer. The hole is stamped with "100V" / "117V" which makes me think it's for a mains voltage selector? I've been wondering about the mains voltage; the transformer is permanently wired with two 110V primaries in series, but mains voltage nowadays is 240V. Might this discrepancy (220V vs 240V) account for the slightly elevated voltages I'm seeing throughout the set? Should I do something about it?

I was going to order replacements for the oil in paper "Suzuki" caps, but I have no idea what kind of ESR these would have had when new, or how important a parameter this is here. I'd like to use axial leaded caps for ease of installation and to keep the original appearance, probably polypropylene ones. I think I can use this 0.0047 cap to replace the 0.005 uF 600V ones and this 0.01 uF part for the other two, but I'd love to hear what you think!?
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Old 17th Jun 2024, 12:56 pm   #4
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Default Re: Trying to fix my father's Trio 9R-59.

The chassis should be earthed. It is the HT power supply which is floated. The HT current in passing through the resistor between HT -ve and chassis makes the HT -ve several volts more negative than chassis/earth. So you just earth the chassis and use it as the reference for most voltage measurements. It's a sort of negative dropper!

You should be OK with those capacitors. The paper ones would not have been brilliant at RF, and on long leads. You don't need audiophile stuff, but you do want well-made reliable ones. Most plastic dielectrics are fine.

Maybe the voltage reg tube hole is on the 9R-59DE/DS model? You can still add one, but it may need a series resistor as well.

David
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Old 17th Jun 2024, 1:58 pm   #5
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Default Re: Trying to fix my father's Trio 9R-59.

Quote:
Originally Posted by Radio Wrangler View Post

Maybe the voltage reg tube hole is on the 9R-59DE/DS model?

David
That's certainly the case. Some sets had just a blank hole in the chassis, whilst others had a wired valve holder in which your fitted your own VR.
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Old 17th Jun 2024, 3:46 pm   #6
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Default Re: Trying to fix my father's Trio 9R-59.

Back on topic please.
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Old 17th Jun 2024, 6:48 pm   #7
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Default Re: Trying to fix my father's Trio 9R-59.

Etaoin, there are a few threads about the receiver, faults and fixes, on this site. If you haven't already, a search for 9R-59 will give you some more relevant info.

Cheers,

Martin
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Old 18th Jun 2024, 12:43 pm   #8
Etaoin Shrudlu
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Default Re: Trying to fix my father's Trio 9R-59.

Quote:
Originally Posted by Radio Wrangler View Post
The chassis should be earthed. It is the HT power supply which is floated. The HT current in passing through the resistor between HT -ve and chassis makes the HT -ve several volts more negative than chassis/earth. So you just earth the chassis and use it as the reference for most voltage measurements. It's a sort of negative dropper!
Ok, so just to confirm, I will not be compromising the safety or performance of the set by replacing the mains lead with an earthed one, and connecting the earth to the chassis? I've looked at the schematic (attached) and cannot see any reason why it would...

Quote:
Originally Posted by Radio Wrangler View Post
You should be OK with those capacitors. The paper ones would not have been brilliant at RF, and on long leads. You don't need audiophile stuff, but you do want well-made reliable ones. Most plastic dielectrics are fine.
Thank you, I have ordered Cornell Dubilier caps to replace the following:
  • [li]1x 10uF 50V, Electrolytic[/li]
    [li]1x 0.05uF 600WV, Paper in Oil[/li]
    [li]3x 0.01uF 600WV, Paper in Oil[/li]
    [li]1x 0.005uF 600WV, Paper in Oil[/li]

The PiO caps will be replaced by 630V polyester, and the electrolyte with like for like. Hopefully this will bring the set back to life... FWIW, while I accept there are differences in quality, I've never bought the audiophoolery arguments about caps and wouldn't dream of spending the silly money some people do. Discussions about how different components "sound" - even cables FFS - only makes me laugh. "A fool and his money are easily parted."

Quote:
Originally Posted by Sparky67 View Post
Etaoin, there are a few threads about the receiver, faults and fixes, on this site. If you haven't already, a search for 9R-59 will give you some more relevant info.
Thank you, I already had a look before posting - lots of threads about the 9R-59DS and some about the unit I've got. I've read most of the relevant ones, but couldn't find anything about my specific symptoms. Nevertheless, it was the large number of similar posts that made me think this was the best place to ask for help!
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Old 19th Jun 2024, 5:51 pm   #9
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Default Re: Trying to fix my father's Trio 9R-59.

Quote:
Originally Posted by Etaoin Shrudlu View Post

Ok, so just to confirm, I will not be compromising the safety or performance of the set by replacing the mains lead with an earthed one, and connecting the earth to the chassis? I've looked at the schematic (attached) and cannot see any reason why it would...
Most of us here would agree, and fit a 3 core lead and earth the chassis.
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Old 20th Jun 2024, 12:27 am   #10
Etaoin Shrudlu
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Default Re: Trying to fix my father's Trio 9R-59.

Thank you. I noticed today that I get a bit of a tingle when touching exposed parts of the chassis...

While waiting for the caps to arrive, I tackled the thing that scared me the most with this project: cleaning the glass dial Terrifying but necessary, since a lot of dust and grime had found its way inside - there were even spots of mold growing on the back of the glass! I wiped it VERY gently with a just barely damp cloth and left it to dry for a few hours, before gently rubbing the greasy spots that remained with a dry eyeglass polishing cloth. The printing at first seemed to hold up really well, but then I noticed some bits coming off Needless to say, I stopped immediately! Thankfully the damage is very minor; two the leading "M"s in "MEGACYCLES" on the right hand side were damaged, and one of the very small digits in the 80m band on the bottom right disappeared; it now read just 4.0 where it should say 4.02 Still, on the whole it's such a massive improvement that I don't regret cleaning it.

I found that one of the two lightbulb fittings was missing, and the one remaining bulb was pretty lacklustre, so I opted to fit the radio with LED dial lights. Two warm white 3mm LEDs either side, pointing into the edge of the glass, and a red LED top left & right, pointing towards the centre of the dial, and mounted behind the glass, to illuminate the pointers. I imagine some restorers frown upon replacing the original lighting but to my eyes the result is simply stunning. The only downside I can see (apart from no longer being 100% original) is that the signal strength indicator is now harder to see - but I've got a plan for that...
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Old 20th Jun 2024, 5:08 pm   #11
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Default Re: Trying to fix my father's Trio 9R-59.

If you haven't already done so, replace C28. You should use a Class Y capacitor in that position for safety. When the chassis isn't earthed, a 10nF capacitor will give you quite a tingle when wired as shown on the circuit. Until you get a proper class Y capacitor, it would be a good idea to disconnect the existing C28.

The low reading on pin1 of V2 and V3 may be an indication that V3 is in need of replacement. You could swap V2 and V3 to see if that makes a difference. The voltage will vary quite a lot between the different bands and at different points on the dial. So long as V3 oscillates at across all the bands, there isn't a major problem.

Paula
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Old 20th Jun 2024, 5:28 pm   #12
Etaoin Shrudlu
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Default Re: Trying to fix my father's Trio 9R-59.

Quote:
Originally Posted by frsimen View Post
If you haven't already done so, replace C28. You should use a Class Y capacitor in that position for safety. When the chassis isn't earthed, a 10nF capacitor will give you quite a tingle when wired as shown on the circuit. Until you get a proper class Y capacitor, it would be a good idea to disconnect the existing C28.
Thank you, I was actually thinking I would do this, but wasn't sure whether the capacitor is even needed? Apart from anything else I guess it helps reduce contact wear on the (rotary) mains switch? I'm in the process of rewiring the set with an earthed mains lead and noticed something unusual: the previous (non differentiated) cable had one lead going via the fuse to one end of the transformer primary, and the other lead going through the mains switch to the other side of the primary. This is stock configuration, as confirmed by the schematic, but I would normally expect the fuse and switch to be on the same (brown) lead, and connected to live, with the (blue) neutral conductor going straight to the transformer. This may not matter for countries that use a reversible plug (e.g. the US and most of Europe) but with British wiring that has dedicated live and neutral plug positions shouldn't the switch and the fuse both be on the live wire? Should I change the radio so it's wired like this? If so, should the "Y" capacitor be on the live or the neutral - or should I perhaps have one on each?

Quote:
Originally Posted by frsimen View Post
The low reading on pin1 of V2 and V3 may be an indication that V3 is in need of replacement. You could swap V2 and V3 to see if that makes a difference. The voltage will vary quite a lot between the different bands and at different points on the dial. So long as V3 oscillates at across all the bands, there isn't a major problem.
Ah, interesting, thank you! I will try this once the set is wired back up. I found a more complete version of the document that listed the voltages I used as reference when testing, and it turns out it starts by informing how the controls should be set before measuring - which of course I had not done The document is actually for the Lafayette HE-30, but I believe that radio is basically identical to the 9R-59.
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Old 20th Jun 2024, 8:14 pm   #13
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Default Re: Trying to fix my father's Trio 9R-59.

I made a PDF of the voltage measurement procedure for the Lafayette HE-30 (which afik is identical to the Trio 9R-59) and I'm attaching it here for the benefit of future tinkerers.
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Old 21st Jun 2024, 9:34 am   #14
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Default Re: Trying to fix my father's Trio 9R-59.

I noticed a couple of asterisks had gone missing from my voltage measurement PDF - here's a fixed version!
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Old 21st Jun 2024, 10:41 am   #15
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Default Re: Trying to fix my father's Trio 9R-59.

I changed to a mains cable with an earth lead, which I connected to a screw through the chassis, but I left the live & neutral wires as they were for now. The chassis no longer tingles, and the RCD does not trip I've also fitted a green LED to the signal level meter, with the exact position determined experimentally to provide the best possible illumination of its scale and pointer. I tried red and yellow as well but found that green proivided the best readability - it is also reminiscent of the "magic eye" signal level indicator tube fitted to some old tube radios, which also have a green glow.

When testing the radio I was actually able to get a few stations, on the 4.8-14.5 MHz band, but reception is very poor. This could be because I only have a length of wire as antenna... The sound rhythmically fades in & out with a fixed period which doesn't seem right (~0.5-1Hz). Stations also seem to drift over time and I have to adjust the band spread (fine tuning) every minute or so to keep listening.

I tried swapping the V2 and V3 tubes as suggested by @frsimen but it didn't seem to make any difference.

The set goes completely silent if I activate the Q-multiplier, regardless of where I set the associated frequency knob. In fact the frequency knob never seems to do anything at all. I can only receive when the selectivity knob is in the fully clockwise AM-CW-SSB position (Q-multiplier "off"). This may be perfectly normal since reception is so poor - I imagine "selectivity" only works when you've got a strong signal, or perhaps there's something wrong with the Q-multiplier tube (6AV6)? I've probably misunderstood several things here!
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Old 21st Jun 2024, 5:39 pm   #16
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Default Re: Trying to fix my father's Trio 9R-59.

Old valve radios do tend to drift. Good ones settle down after a warm up period, less good ones just keep on drifting! That said, I suspect your 9R-59's drift is probably normal for the type.

The pulsing effect could be due to some local interference source, rather than a fault in the radio. Can you receive anything on Medium Wave? There are still some strong signals in the London area, so you should be able to hear them. A bit of experimentation with the aerial will pay dividends.

You will need a strong signal to allow you to set up the Q-multiplier, something on medium wave will be ideal and you shouldn't have too much of a problem with drift on that band. From what you have said, it could be that the Q-multiplier's alignment is wrong. The HE30 manual explains how to align the Q-multiplier on page 12. If that doesn't help the valve could be faulty, or you may need to switch to MVC and back off the RF gain control. Once set up, it should behave as described in the book.

Paula
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Old 22nd Jun 2024, 7:30 pm   #17
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Default Re: Trying to fix my father's Trio 9R-59.

I've got a 9R-59DS here in it's original box that I've not yet had chance to do anything with. If it helps at any point I'm happy to pull it out and compare voltages and component values etc. I'll be following quietly on the sidelines unless called upon
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Old 23rd Jun 2024, 9:47 am   #18
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Default Re: Trying to fix my father's Trio 9R-59.

The DE and DS versions are completely different to the 9R-59.
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