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Old 2nd Jul 2016, 4:13 pm   #1
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Default Another Trio 9R-59DS.

Inspired by this thread I decided to check out my own Trio 9R-59DS.

https://www.vintage-radio.net/forum/...d.php?t=114061

I bought my set new around 1970 complete with matching speaker. It has remained unused for the past 25 years though, except for the occasional functionality test.

I connected a decent aerial and earth and switched on. I then tuned in a MW station and found that the sound was very woolly. I don't go in for poking and hoping or wholesale component replacement, so out came the service manual and the DMM.

Voltage checking on these sets is very easy where the valves holders are mounted on PCB's. It's possible to check voltages from the top of the chassis. You just have to remember to count the valve pins anti-clockwise. Checking voltages on the output valve, a 6AQ5, showed there was +2VDC on the control grid, so I switched off. Naturally "that capacitor" in this case C34 a 0.01uF "oil" type rated at 630V was suspect. I snipped the end of it going to the control grid of the 6AQ5 and switched on again. The control grid now read close to 0V. Checking the voltage on the snipped end of the capacitor showed 13VDC, so it was definitely faulty. I decided that a new 630V capacitor would be over the top, so I fitted a 400V polypropylene component. The PCB construction makes component replacement very easy, no need to unwind wires from tags or disconnect other components. There was now 0V on the control grid of the 6AQ5 and the set sounded better, but not as good as I remembered it.

Further voltage checking on the output valve showed 3.75V on the cathode compared to a figure of 6.5V in the service sheet. Fitting a new 6AQ5 resulted in better sound, but there was now 8.79V on the cathode, which seemed a bit high. The cathode resistor R35 was a 330R component which measured 337R. I disconnected one end of the cathode bypass capacitor C37 10uF, but the cathode voltage remained the same. Whilst the bypass cap was disconnected I checked it with an ESR Meter. It was fine, so I reconnected it. I concluded that the new 6AQ5 had very good emission.

I then started to check all the other voltages against those in the service sheet, starting at the power supply. The 205V HT supply read 219V which I put down to high mains voltage. The set only has voltage selections for 110VAC to 120VAC and 220VAC to 240VAC. However the 191V HT supply was reading close to 150V. It took me a while to realise the optional OA2 150V voltage regulator was connected directly across this supply . As other voltages were likely to be affected I temporarily removed the OA2 and the voltage leapt up to 198V.

Checking the other voltages showed they were all high with one exception. High cathode voltages point to excess anode and screen currents which you'd expect to lead to low anode and screen voltages, but these too were high. Leaking anode and screen grid decouplers could be ruled out and the screen dropper resistors tested fine. The exception to the high voltage reading was the cathode of the BFO which read 8.6V compared to 30V in the service sheet. When measuring this voltage with the BFO turned off the meter itself effectively becomes a cathode resistor, so the reading depends on the meter's internal resistance, which in the case of s DMM is very high. Back in the 1960's when the service sheet was written, moving coil meters would have been the order of the day.

I rechecked some readings with a 20kohm/volt meter and although they were now lower they still differed from the spec. I can only assume that a meter with low sensitivity was used when compiling the service manual. Has anyone else had problems with voltage readings from these sets?

The only other obvious fault was a blown dial lamp. These are miniature bayonet fitting types specified at 6.3V 0.15A. However 8V 0.15A lamps are fitted. I can't find a source for 8V lamps so it looks like I'll have to fit 6.3V ones.

A functional check showed that it was possible to receive SSB and CW signals without difficulty.

The next step will be to get out the signal generator and check dial calibration and sensitivity. I won't be adjusting anything unless it's obviously wrong.
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Old 2nd Jul 2016, 4:27 pm   #2
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Default Re: Another Trio 9R-59DS.

Low sensitivity on these is sometimes due to deterioration of the wax used on the RF coils; with age it undergoes some sort of chemical degradation which robs the tuned-circuits of their "Q".

(the same problematic wax is found in some 1960s/1970s/1980s Japanese hifi tuners and VHF amateur radio transceivers, often slathered all over the FM local-oscillator PLL tuned circuit and associated components. Drift, low output and in the worst case a non-oscillating oscillator - can be the results).
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Old 2nd Jul 2016, 9:17 pm   #3
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Default Re: Another Trio 9R-59DS.

I've just realised that the service manual is for a version having a mains transformer with taps for 110VAC and 117VAC only. Obviously intended for the US market.

The circuit in the operating manual shows the correct transformer with two primaries which can be connected in series or in parallel. The only other difference I can spot is slightly different smoothing arrangements.

However the test voltages differ between the two circuits and not all differences are down to the different mains voltages. The are obviously some errors in one or both manuals. The most glaring difference is in the cathode voltage for the BFO. 30V in the service annual and 10V (which is much more realistic) in the operating manual.

I'm going to have to check my voltage readings again.

Howe
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Old 2nd Jul 2016, 9:51 pm   #4
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Default Re: Another Trio 9R-59DS.

In the schematic I'm looking at the BFO valve's cathode voltage is also given as 10 volts, I presume that's the open circuit cathode voltage?

With the BFO switched on, the cathode is connected to HT-ve (chassis) so far as I can make out.

Lawrence.
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Old 2nd Jul 2016, 10:07 pm   #5
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Default Re: Another Trio 9R-59DS.

You are correct in all respects.
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Old 9th Dec 2016, 4:36 pm   #6
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Default Another Trio 9R-59DS

I have just got hold of one for restoration. The RF Oscillator had been modded for an FET and there was an NBFM adaptor fitted (R.A. Penfold - PW May 1980). I think someone must have tried to use it for CB reception though given the performance at 27MHz I doubt they got much.

I have removed the FET, NBFM board and associated power supply, replaced the missing ECC85, restored the wiring and the set is working.

So to my query:- on the underside of the chassis between the HT capacitor and socket for the OA2 there are two earth tags. One has a 470R 1/2 watt resistor which appears to be original and is the same type as the other resistors in the set. The other end of the resistor is not attached. It's not obvious where it goes, everything in the area is part of the HT circuit and I can't find a 470R on the circuit.

Any ideas please?

Last edited by AC/HL; 9th Dec 2016 at 5:15 pm. Reason: Thread reopened
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Old 9th Dec 2016, 5:21 pm   #7
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Default Re: Another Trio 9R-59DS.

I've looked at the circuit, and to the modifications that featured in the first Radio Constructor article in October 1970, which covered mods to the PSU, screen grid resistors, RF gain control, oscillator stability, and addition of the crystal calibrator. No sign of a 470R resistor that I can see - either originally or as a later mod. One of life's mysteries I guess. I did most of the mods on mine back in the early 1970s, and the power supply mods did provide a worthwhile improvement, in for example, the reduction in hum, by fitting a choke in place of the resistor, and other alterations. As the set doesn't have a built-in speaker, when listening on 'phones the hum had been quite marked.

If you don't already have it, this issue of Radio Constructor can be downloaded free from here:

http://www.americanradiohistory.com/...RC-1970-10.pdf

There were two further articles in March 1971 and April 1971, which covered a further eight modifications and alignment information, which can be found here:

http://www.americanradiohistory.com/...RC-1971-03.pdf

http://www.americanradiohistory.com/...RC-1971-04.pdf

Good luck with it.
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Old 9th Dec 2016, 6:45 pm   #8
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Default Re: Another Trio 9R-59DS.

I've just had a look at my own unmodified set which came prewired for an 0A2 voltage stabiliser.

One of the tags is the earthing point for the common tag of the smoothing capacitor.

The other tag has a 220k resistor with a parallel capacitor running from it to pin 1 of the 0A2.

No sign of a 470R resistor.

We've been here before:-

https://www.vintage-radio.net/forum/...50&postcount=9
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Old 12th Dec 2016, 12:32 pm   #9
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Default Re: Another Trio 9R-59DS.

Thanks All,

I think I will just remove the resistor and move on.

I wouldn't expect the sound quality to be 'wooden box radio' but this one is very harsh and hissy even with the RF gain turned down a bit to prevent overload so I have something else to investigate.
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Old 16th Dec 2016, 7:34 pm   #10
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Default Re: Another Trio 9R-59DS.

No. These were great CB receivers. Not so helpful when you wanted 10m.
Also good at the 20m band full of BC really on 15MHz.

Oh yes - any they bite! 2 wire mains lead and a pair of caps floating the chassis between L&N.
If you don't connect an earth at best they tickle the operator.
If you happen to touch some earthed object and the chassis of the set at the same time then you will know about it.
I have not forgotten.

Thanks for the nostalgia trip.
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Old 16th Dec 2016, 8:40 pm   #11
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Default Re: Another Trio 9R-59DS.

Indeed Jon. The 470 KHz IF was OK at the LF end, but the higher up you tuned, the louder the images became! By 10m, there was almost no difference between the wanted signals and the images. And mine drifted like the clappers on any frequency higher than 20 MHz, despite having the HT stabiliser fitted.
And I certainly recall the slight 'buzz' you could get if you brushed the back of your hand on the metalwork. Oh, happy days.
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Old 16th Dec 2016, 8:48 pm   #12
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Default Re: Another Trio 9R-59DS.

I've recently acquired one of these receivers from forum member "Doug_h" [BTW, thanks Doug!]

It works, but is somewhat deaf and the antenna-peaking control shifts the local-oscillator by quite a few KHz. I'm thinking that there must be a high-impedance in the frontend that's common to both the signal-frequency stages and the LO - so I'll be checking-out the various earth-points and - first of all - the contact-fingers that ground the rotors on the main- and bandspread-tuning capacitors.

With a 455KHz IF and only two signal-frequency tuned-circuits it's never going to have impressive image-rejection - even an AR88 with three SF tuned-circuits only claimed a wanted:unwanted rejection ratio of 200 at 28MHz.
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Old 17th Dec 2016, 5:22 pm   #13
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Default Re: Another Trio 9R-59DS.

Thats all part of the fun isn't it.

I wish I still had mine & it's matching speaker - funny I don't remember selling them but I suppose I must have.

Nice S meter.
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Old 17th Jan 2017, 10:20 am   #14
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Default Re: Another Trio 9R-59DS.

My set is equipped with a 0A2 ( wired), and has a valve socket for the calibrator, and a socket for a HC-6U calibrator xtal ( both not wired). Is it known what valve was intended to use? Can only find the transistor calibrator....
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Old 17th Jan 2017, 1:29 pm   #15
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Default Re: Another Trio 9R-59DS.

The crystal calibrator used a 6BA6 valve. The chassis should already be punched for the valveholder and a tagstrip installed at the factory. If you go to the first link that I posted in post 7 above, you'll find the wiring layout. The circuit was included in the Trio Service Manual.

Hope that helps.
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