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Old 22nd Oct 2020, 1:06 pm   #41
Peter F4VSA
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Default Re: Hudson help

Sorry for the delay but a few more pictures of my FM208
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Old 23rd Oct 2020, 8:38 am   #42
Jon_G4MDC
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Default Re: Hudson help

Nice pictures Peter, I wonder if there is a date on any of the electrolytics? It would be interesting to know the approximate year it was made.
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Old 23rd Oct 2020, 2:02 pm   #43
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Default Re: Hudson help

It appears early to mid 60's, about the same time as the Cambridge and I note when looking carefully at the images the blacks Hunts are doing what they are good at and the cases are starting to crack!

I still have not got back to do any further investigative work on mine.

Ian
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Old 9th Nov 2020, 4:55 pm   #44
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Default Re: Hudson help

Having finally been able to have the time to get at the radio again, I followed the kind advice on two fronts, firstly I dug out a signal generator that covered the TX crystal frequency and watched it on the 'scope and then compared to a known good one and they both behaved in the same way. Putting the TX crystal back in, nothing, although the RX crystal did fire up in the TX oscillator! Anyway, with the "proper" TX crystal back in and the scope on the cathode of the oscillator, touching a 2.2nF between the anode and deck resulted in oscillation. OK, so I had a look at the value of capacitor between the anode and deck. C18 is shown in the circuits diagram, but there is no sign of it ever being fitted. 5pF had no effect but fitting a 25pF and it was away! So how has the thing ever worked?

Checking with a wavemeter showed about 17MHz, from the first multiplier, which seemed right (x2), but the second multiplier did not want to play. Adding 5pF across the coil gave some output, but its waveforem was low and not very nice. The wavemeter showed circa 27MHz coming out of the second multiplier; i.e. crystal frequency x3. To cut a long-ish storey short, it transpired that the first multiplier was selecting the third harminic of the crystal (I should have checked with the wavement to see what else was coming out, rather than just looking for what I wanted). Padding the first multiplier coil with 5pF, a re-tweak and a check with the GDO showed it now peaked up at the second harmonic and the result was a much larger signal out of the second multiplier at circa 35MHz.

However I could not get the third multiplier to give any output at all. A quick look at the remaining coils (final multiplier anode and PA) with the GDO shows they are all peaked at circa 100MHz. This is where it gets interesting as the circuit I have just shows two variants of the radio and neither covers 100MHz! One again down the garden path I went.... The trimmers from the final multiplier onwards are all beehive types and all the anode ones (obviously!) have HT on them, just to give life a bit more bite as you try to adjust them.

I used the GDO to get the final multipier anode to be resonant at circa 70 MHZ, by padding the coil with 10pF and adjusting the trimmer, but still no output, despite carefully tweaking the anode trimmer. All voltages seem about right and the valve (EL85) exchanged (I was not expecting that to do anything but I swopped it just in case). Hmm, so what's going on here?

That is far as I have got at the moment.

Once again thanks for the help.

Ian
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Old 7th Dec 2020, 8:41 pm   #45
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Default Re: Hudson help

Well, having been home for a few days I had chance for a quick look at the Hudson in between gardening and household jobs. The outcome, however, was a classic case of one step forward and one step backwards.

After getting the tuned circuits around the PA to be resonant circa 4m, then finding out where the PA screen grid volts has gone, it suddenly developed 1/2 watt of RF, not quite the 5-6W is should be but a start. Then suddenly the output dissapeared and the 70.26 became 73.something. That might have just been the output falling below what the el-cheapo DFM would read, but it did appear stable and dissapeared when the crystal was pulled. No amount of cajoling would bring the output back.

I suppose when I get home again I will have to start looking from the oscillator onwards again.

Keep smiling.

Ian
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Old 8th Dec 2020, 9:39 am   #46
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Default Re: Hudson help

Well done Ian - never say die!
It'll still be there after all.
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Old 8th Dec 2020, 7:55 pm   #47
Peter F4VSA
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Default Re: Hudson help

Hello all, sorry for the delay in replying. I have had a look at my Hudson and none of the electrolytics have any dates on them and yes the Hunts black caps are all cracking as usual. The unit is full of Mullard OC45's etc so I would guess a mid 60's date. The only RF transistor I can see the number of is a 2N1742 which is similar to an AF139.

It's still reserved for you Ian!

Peter
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Old 9th Dec 2020, 10:08 am   #48
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Default Re: Hudson help

Thanks all.

Over the years you get some jobs/projects that seem to fight all the way, but this one is one of the worst I have had. The transmit side seems to be unconditionally unstable. I do not know whether an enforced sepration is actually a good thing or a bad thing. In one way I cannot "get on with it", but in another it forces me to go away and think, rather than my usual failure mode of going round in circles and refusing to leave it!

73 all

Ian
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Old 9th Dec 2020, 11:39 pm   #49
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Default Re: Hudson help

Hello Ian, I read your posts about the TX the same way.

It does seem very unstable, but is there any condition when it is stable? I suppose that is yet to be be seen.

I have an FM10D Pye Cambridge for 10m whose RX gave me pain for many years. It works now but for a very long while it was a nightmare of feedback and instability.
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Old 18th Dec 2020, 1:39 pm   #50
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I had a few days free to look at it again, this is what has occured.

Firstly I decided to have a change and look at the handset that was aquired separately from the radio, but actually has the correct multi-pin Painton plug on it. It took a bit of what my father refered to as jiggery-pokery to get the carbon mic insert to connect (there were a few bits missing inside the mouthpiece), but eventually it produced an output and nothing rattles around inside.

That leaves the handset lead, this is quite a heavy (formerly coiled) cable that now consists of a series of three-dimensional waves along its length. So, do I try to re-coil it and if so how? Or do I leave it as it is and make the best of a bad job? It does look a mess though. Modern ones are a lot thinner and would not look right plus the need for more cores than later arrangements.

Returning to the RF side of the radio. As mentioned earlier, the tuning on this is ultra critical and if you get the tuning of the final multiplier and PA correct, these two stages will produce RF with no crystal! Not a good situation. So back on the bench and connected to the old Marconi 2950 to look at the power output, a small el-cheapo DFM and a W30AM listening on 70.26 I went back and forwards and back and forwards, swore a few times (get the hint?), repace the EL85 I got a test lead wrapped around and bent the pins such that it lost its vacuum, and eventally managed to get 4.5W out; which was on 70.26 and stopped when the crystal was removed. Listening 12.5 kHz either side on a Key KM80 showed a little signal to the HF but nothing to the LF. Looking at the RF output on a scope showed it to be "nice". Good technical description.

As mentioned, adjusting beehive trimmers seems to require a technique I have to learn after over 5-decades at this, is there any other way than carefully trying to push them round with an insulated trimming tool? It seems rather crude and due to the way the coarse thread is arranged, they then move axially under the pressure, such that when it is removed the capacitance then changes. I would say fun and games, but that would require a re-definition of the word fun.

What would anyone recomend for locking beehive trimmers? It seems to need to be hard, but needing little strength / force to break the seal.

The radio should generate about 6W or so ('3-10 with about 270V), I did not manage to pad the PA coil as when I did so it went unstable again, and being on a styrene former you cannot tweak the windings around. At the moment the beehive is only a fraction of a turn off its maximum capacitance. So some more experimentation may be required here.

There were also a few heart stopping moments with the lash-up that connected to the Pye style RF connector on the front, I will have to look out of a plug / adaptor as I would rather not change the connector on the radio. For the time being, I have now temporarily soldered a lead to the back of it.

The squelch is still possibly the worlds most useless one, it opens at circa 10 microvolts but at least it stays open down to under 1 microvolt. You need some hysteresis but surely not that much. This is not shown on the circuit diagram I have and I did draw it out some time ago, but in ther meantime I have managed to loose the note, so next time is is back to investigating it again.

Interestingly, there has always been an inverter whine on RX, changing some electrolytics around the class A single transistor audio / modulator o/p stage reduced it to acceptable levels and wandering around with a scope only showed it at trace levels. However, after it had been on for five hours it was right back to virtually nothing. Something re-forming somewhere.

Having recently had some contacts on 4m AM, I arranged with a friend to listen out for me and to my relief the radio actually behaved itself. It was only about 5miles, but there is a blooming great lump of sandstone in the way. The radio is actually quite sensitive, being on a par with the W30 (non-FET front end variant) and the transmit side about as copyable as an MF6AM. So a result, as they say.

All I have to do now is ensure it stays behaving itself, find a way to lock the trimmers, sort out the squelch, sort out the mic lead and finally convert it from positive earth, that arrangement has resulted in the odd shower of sparks! These radios were supposed to be switchable, the much modified (vandalised?) one I have retains some of that facility, such as the chassis mounted switch and some bits of cut off wiring. As mentioned before, this one is at odds to the circuit diagram and has had some professional changes at some point as well.

I have a Hudson control box as well, but looking more closely, this appears to be for a later version and not the AM108. Possibly an FM208? One for another day methinks.

73 and seasons greetings all.

Ian
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Old 19th Dec 2020, 10:28 am   #51
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Default Re: Hudson help

Sounds like you are making good progress Ian. Just to answer your question - in the olden days there was a tool for adjusting beehive trimmers, a round paxolin (?) tube with a hex (?) inside profile. They were part of the Pye trimming tool kit which we were issued as part of our main tool kit. The rotation of the trimmer was fixed with a spot of candle wax once they were tuned.

Mic lead-wise, is the lead used on the Clansman pressel an option?

Merry Christmas,

Martin
G4NCE
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Old 19th Dec 2020, 7:26 pm   #52
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Default Re: Hudson help

Found it!
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Old 19th Dec 2020, 7:51 pm   #53
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Default Re: Hudson help

We always used a length of polythene 'aquarium tube' [as used to feed the fishtank bubblers] to tweak Beehive trimmers.

Cut a couple of inches from a reel and pop it onto the trimmer's top: you were then well-away from any capacitance-proximity-effects and also separated from contact with the 400V that could be on the anodes...

When tuned, we put a blob of Tipp-Ex™ on the trimmer, followed by some cheap nail-varnish. This really made it hard for any 'fiddler' to deny their involvement.
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Old 20th Dec 2020, 5:19 pm   #54
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Default Re: Hudson help

Good to hear of your success Ian! Are you testing at the Lichfield or the London QTH?
If sandstone is the obstruction I suppose maybe not in the London area.

I also dislike beehives - any option to replace them? I wonder what value they are?
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Old 21st Dec 2020, 10:00 am   #55
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Default Re: Hudson help

Thank you Sparky and G6 for the information on the proper way of adjusting Beehives, I have obviously led a very sheltered life thus far. I had looked around the workshop at home to see if I had anything that would slip over them but nothing practical appeared. I am intrigued by the internal hex on that trimming tool though, given that beehives are round, I don't doubt it at all, I am just intrigued! Regarding fishtank tube, the only fishtanks I come across are a type of elderly railway signalling relay, although if I pass a pet shop I may well have a look; I had wondered about playing with heatshrink tubing and a spare beehive. Anyway, it answers my question, in the short term at least I may have to go on using the same technique - carefully.

With regard to locking them, Tipp-Ex is a good call, that is something I had not thought of and will probably use. I was thinking along the lines of cellulose type paint, but unsure. With regard to nail varnish, I am not sure if my preferred colours would match the radio!

As to replacing them, it had crossed my mind, they are mounted above the chassis, each on its own small Paxolin (other forms of SRBP etc. are available) dias and they could probably be changed but it would probably end up looking a bit of a bodge as the assemblies are nicely engineered. As to the value, that has been a handicap since the start as the poor quality scan of the manual I have is all but unreadable when it comes to component values and that has led to a few frustrating moments. In fairness though it has been helpful in terms of understnding the general arrangements. As I think I stated earlier I did find a manual a year or so ago, but it went missing courtesy of a low-cost wing footed courier. The radios with it turned up on eBay.

Martin, unfortunately I do not know the Clansman pressel; the Hudson handset lead is circa 1/4 inch outside diameter with 6 cores.

Jon, the radio is at home in Staffs, as is the workshop, which is why there are long (sometimes frustrating) gaps in being able to "play" with it. It is bit big to bring down to London when circumstance distates I have to be here in caring mode. As I said last time, there is a plus side to this situation and that is it forces me to standback and think.

73 and seasons greetings all.

Ian, G8KSZ.
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Old 22nd Dec 2020, 10:15 pm   #56
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Default Re: Hudson help

The Clansman pressel cable has 7 cores plus a screen and is 5mm diameter cable Ian. It’s a bit difficult to measure the coil overall but it looks like it’s just under 25mm.

If you want help with any tests I’m wondering if I could hear you from here on the hill in Great Barr? I can’t transmit AM but can receive on 70MHz and talk back cross-band to HF, or 2m maybe?

Cheers,

Martin
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Old 22nd Dec 2020, 10:29 pm   #57
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Default Re: Hudson help

This was what was always the best about 70.26MHz!
It went on on 2m but survived longer on 4m.

If you can TX on any mode then use it. The bloke at the other end will bust a gut to copy you.
My W30AM had slope demodulation for FM and a BFO otherwise.

I didn't ever sort out the TX for multimode, and you can't key a DC/DC inverter, but 80% mod of "whistle morse" completed many QSOs. May it live again.

This is the way. D-Star, DMR, FT8, and all those - pah... ffft
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Old 17th Jan 2021, 4:56 pm   #58
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Default Re: Hudson help

I hope everyone had a pleasant festive season and once again, thanks for past help. I had the opportunity to become acquainted with the AM108 once again. It is definitely getting better, I even dared to screw the bottom screening cover on, something that is usually guaranteed to stop things working.

I tried to use Tipp-Ex to lock the Beehives, but found the latest incarnation to be a lot more fluid than I remember it and it just runs straight through, so I will have to hi-jack some of her ladyships surplus nail varnish and try that - a risk assessment states that I need to ask first though.

The RF seems stable (for the time being at least). I did have a brief heart attack when the RF power meter stopped displaying anything, but this time it was found to down to the state of the co-ax inside the Pye connector, I made up an adaptor lead using a plug with a length of co-ax already attached that I acquired and have had hanging around for decades. There was a slight gap in the insulation on the inner conductor, probably damaged a long time ago when the braid was cut to fit the plug and it seems to have been shorting. Anyway, sorted that out and back to 6W out. I must admit to being just a tad paranoid at the moment though, wondering what the radio is going to do next.

I decided to have a look at the somewhat useless squelch circuit, a final doodle of it it is attached, the relay switches the RX audio from the detector. This does not appear on the circuit diagram I have, which is dated 1961. It was difficult to trace out due to the way it was installed. It seems a later addition (by Hudson?) as some of the resistor leads are just surface soldered to tag strips rather than wrapped and soldered, but the mounting bolts have red lacquer on the nuts. It is based around a relay and a couple of OC-somethings, black glass cased but installed so I cannot read the numbers, the circuitry makes use of unused contacts on the relay base as tags, which caused a little confusion at the outset, as did the coloured sleeving on the transistor sleeves, which fiendishly contrived to have the three colours on different leads on each transistor.....

A few images, with the relay removed from the socket are attached. I have only just twigged that there is no diode across the relay coil.

Anyway, after half a dozen attempts I decided the attached sketch bore some resemblance to the installed circuit. To recap, the squelch look circa 30+ microvolts to open it once it was closed, not really practical. First of all, I disconnected the 25 mfd electrolytic, leaving just the one hiding in the corner. This took it down to just below 5 microvolts, then removing the 1k across the relay and switching transistor took it down to just under 2 microvolts to open; still not particularly good. I cannot help thinking there must be a better arrangement though...

Over Christmas, whilst trawling around various web sites, I found a new unused old thick 6 core telephone handset lead, which I duly bought and fitted, the colours were pretty much the same as well. Looking at the Modulation Meter, you have "talk it up", I suppose old telephone handsets may not be the most sensitive, but I am wondering if the carbon insert has lost a bit of its "oomph". There is no mic gain adjustment. I had another 4m AM contact using the radio, an acquaintance was using 70.26 AM for talkback during some tests on top band AM so I surprised him by appearing. He did comment that the TX audio became weaker as time passed though, but whether that was the insert or me fading away I am not too sure. I suppose I need to look for a "new" carbon insert to check.

Martin, come the summer it might be worth having a play, it would be easier if I still lived in Perry Barr though! I can just about work Arthur on 4m FM from Great Barr, when I am at home.

Jon, this is better than trying to re-invent the mobile phone system. Allegedly. I meant to comment earlier about your "fun" with a 10m Cambridge, I have long lusted after one of those, for no sensible reason in particular. The only other ex-pmr radio I really had stability problems with was a Bantam, with its cascaded power supply arrangement feeding through IF and RF stages stacked on top of each other, DC wise.

73

Ian G8KSZ
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