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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 19th May 2023, 11:30 am   #21
G4XWDJim
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Default Re: R 103

Malcom, I've just photo'd the info you need not realising Richard had already done it. Pleas give me your email address and it might be a larger file.

This had the benefit of a second pair of hands stretching the page flat.

Jim
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Old 23rd May 2023, 5:40 pm   #22
Malcolm G6ANZ
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Default Re: R 103

I've started to take the Rx apart. With a couple of knobs and some of the screws the screws and nuts are rusted in. The main problem being the knobs. I've tried putting thin oil down the threads and also heating the end of the screw with a soldering iron, all without success. One of the knob screws has how sheared off the screw head. Before I attempt to drill out the screw is there any other way to get them out? The screws with nuts on the back can, I think, get undone once the front panel is off.
Jim, the info you sent me is good. Thanks again.

Malcolm
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Old 13th Jun 2023, 9:26 am   #23
Malcolm G6ANZ
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I have made progress on the restoration. I hve removed the waveband switch and coils, they are in a separate sub chassis so come out fairly easily. The sub chassis was very rusty and bent. i cleaned it with wire wool and some fine sand paper and it had come up reasonably OK. One of the coils had its tapped terminal ripped off when the chassis was bent. I repaired the break and its now got continuity. The main problem is the trimmer cap that has got a broken ceramic base, a new one is needed. The coil subchassis is now set aside while I continue with the rewiring and component changes.
The diagrams are slightly confusing as the components are on tagstrips mounted on the chassis sides and each tagstrip is labelled as A,B,C and the components are called ,say, C1A, C2A or C1B etc same value but different position.
Thanks again to Jim and Richard for the documentation.
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Old 13th Jun 2023, 6:05 pm   #24
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Default Re: R 103

That sounds like a great start, Malcolm. Given the chassis was "very rusty", do you propose any way of stopping the rust setting in again?

Richard
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Old 13th Jun 2023, 7:46 pm   #25
Malcolm G6ANZ
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Default Re: R 103

The only rusty part was the coil and bandswitch sub chassis. the main chassis is in good condition , just a bit dirty. I'm going to leave the main chassis as is, as to clean it fully entails stripping it right down which I am loth to do. The sub chassis should now be OK as it will be kept in a warm dry environment not cast aside in a damp cold barn !
The wiring which I am slowly replacing is actually solid core with coloured sleeving. I am replacing these as I had to cut them to extract the side tagstrips. I am using suitable coloured silicon sleeved stranded wire except where I don't need to replace the wire. Does that make sense?
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Old 14th Jun 2023, 9:13 am   #26
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Default Re: R 103

Yes, that all makes lots of sense. Sounds like a good job you are doing there. I like the silicone type wire for vintage renovations with its matt finish, as it blends in better with the old wiring than shiny PVC coated wire.

Richard
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Old 28th Jun 2023, 11:42 am   #27
Malcolm G6ANZ
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Further progres. I've completed recapping the 'RF' tag board. This has the screen grid feed ans decoupling fir the first two valves. Its now back in and wired up. I'm looking for a replacement compression trimmer for the coil pack it is a 4-40pF. The broken one is one of a pair mounted on a bracket, it's only the ceramic thats broken away so the actual capacitor may be OK. Thoughts?
I will also need 6 top caps for the IF valves, if anyone has any they dont need let me know. The 6V6G output is missing, I may have one stashed away somewhere, I'll have to scour the far reaches of the shed.
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Old 8th Jul 2023, 6:03 pm   #28
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Further progress. I now have resonance on the aerial input tuned circuits and the first RF amplifier. Some repair needed on the way. First on the aerial circuit there was a broken wire from one of the coils to the switch wafer. The coil itself was continuous and the break was inside the PVC sleeving so could not be seen. To repair I had to remove the complete coil assembly again. While it was out I rechecked all the other coils and associated wires to the switch wafers. With the assembly refitted there was resonance on both bands . Moving on to the anode tuned circuits on the first RF amplifier. This had no resonance at all. Investigation resulted in three faults, first I misread a resistor I replaced so instead of a 250K I fitted 2.5ohm and a switch which turn the AGC on and off was permanently closed. This put a short across the secondary so killing the resonance. There was still another fault. Under the switch bank there is an earth tag. this had moved and was shorting the switch wafers to chassis. By bending this tag away from the switch the tuned circuits burst into life.
So far I've just been injecting a mV signal into the tuned circuits and looking on a scope for a peak as the tuning capacitor is rotated.
The local oscillator tuned circuits were checked in the same way and were working.
The front panel is now refitted an the tuning dial setup, the calibration seems pretty accurate.
Next step is to construct a power supply and get a 6V6 output valve.
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Old 13th Jul 2023, 6:27 pm   #29
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Default Re: R 103

Update. I have a working receiver, I hope.

By using a Radford LabPack to give the 6.3 volts and 300v for the HT I fitted each valve in turn and injected a signal to the aerial and monitored the grids on a scope. This showed that a signal was getting as far as the first IF then stopping. It seemed that the output from the coil was shorting to chassis. This fault was traced to the output tuning capacitor shorting on the can, by slackening off the capacitor and moving it slightly away from the coil former edge enough clearance was achieved.

There was a seemingly intermittent fault with the frequency changer in that it was reluctant to run at more the about 5.5MHz and sometimes it wouldn't run at all. I think this was due to a low heater voltage caused by my use of thin wire crocodile leads giving a high volt drop when most of the valves were fitted. Using a thicker wire cured this.

I could now see demodulated audio on the grid of the driver valve. I found a 6V6 and with that fitted there was audio on the phone jacks. However there is a lot of hum on the audio. I think this is coming from the PSU being loaded more than its rated output.

Sensitivity: this is about that stated. At 6MHz I can go down to 7uV and still see demodulated audio, at 3MHZ this closer to 5uV.

Before I put a real aerial on it I want to build a decent PSU so it can run without any hum.
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Old 19th Jul 2023, 8:55 am   #30
Malcolm G6ANZ
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Default Re: R 103

Apart from the 6V6 output the set is up and running. Good sensitivity, however there is a lot of distortion on the audio I'm putting this down to the lack of feedback from the output stage (it's not there!) I have a 6V6 but with it fitted the set draws too much current from the Radford power supply and it gives a lot of mains hum. Without the 6V6 in there is virtually no hum present.

Waiting for the delivery of an HT transformer which can supply the required current so the 6V6 can be used.
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Old 19th Jul 2023, 8:37 pm   #31
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Default Re: R 103

Hi Malcolm, try a lower power valve such as a 6F6 or one of the KT** series, and / or increase the cathode resistor

Ed
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Old 21st Jul 2023, 11:54 am   #32
Malcolm G6ANZ
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Thanks Ed, I fitted a higher value cathode resistor and it made no difference. I investigated the HT supply. The Radford pack is meant to give out 280v in fact its nearer 320v. So i have put a resistor in series with the supply, so with a current drawn of 80mA and needing a volt drop of approx. 100v a 1.2k resistor is needed. The closest I had, with a high wattage rating was 1.8K with this in circuit the HT volts dropped to 220v and the hum was reduced to a much lower level. So it was the high HJT causing the problems.
Next is to get the BFO working correctly. It runs at 465KHz (IF frequency) but doesn't seem to have much effect on SSB.
I have got a new HT/ LT transformer so I will be making a dedicated PSU to give the 200v and the 6.3v required.
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Old 21st Jul 2023, 3:36 pm   #33
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Default Re: R 103

Getting the right relative levels of signal and BFO is always tricky when trying to resolve SSB using a diode detector really intended for AM.

My usual approach is to tune for maximum monkey chatter with the BFO and AGC turned off then turn the RF gain right down to silence the receiver and turn the BFO on.

Then bring up the RF gain slowly.

Or fit a product detector which is a good bit less pernickety about the relative signal levels...
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Old 7th Aug 2023, 11:34 am   #34
Malcolm G6ANZ
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Default Re: R 103

i think the R103 is now finished and working as well as can be expected. I have rewired the IF gain to work as an RF gain as it was overloading on strong signals making SSB difficult to resolve. It is still a bit tricky to resolve SSB with a simple BFO but it can be done.
Over the weekend there was a contest running and on the 40M band I heard alot of European stations and one Lithuaniun, so the sensitivity is good. The next step is to improve my aerial. At present its a 20 ft long wire with no ATU just straight into the receiver.
Many thanks to all who have helped me get this receiver working again.

Malcolm
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Old 8th Aug 2023, 1:04 pm   #35
G4XWDJim
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Default Re: R 103

Well done Malcolm. I repaired a Canadian R103 some 20 odd years ago that seemed to have a similar performance.

Jim
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