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Old 4th Sep 2020, 9:35 pm   #21
Jon_G4MDC
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Default Re: Hudson help

Thanks Ian for coming back with that.
Now there is lots to work on.

Sleep well and I hope the paint dries before next rain!
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Old 4th Sep 2020, 11:25 pm   #22
Peter.N.
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Default Re: Hudson help

I used to service Hudson radios in a local FX4 taxi fleet, I seem to remember they had a rotary converter for HT. This was in the '50s mind.

Peter
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Old 5th Sep 2020, 10:16 am   #23
Jon_G4MDC
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Default Re: Hudson help

The TX crystal is the same as Pye Cambridge series 70.26=8.7825

I'm a little surprised that the RX crystal is a fundamental on (Fs-10.7)/8 that would make it 59.56/8 = 7.445MHz I suppose. My first port of call with this would be to check that there is an adequate amount of 59.56MHz at the first mixer and the multipliers are doing what they should. (GDO for this?)

The Cambridge uses (Fs-10.7)/2 = 29.78MHz (for 70.26) so also injecting 59.56MHz.
Of course a crystal that high in the 1960s had to be made as a 3rd overtone.
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Old 5th Sep 2020, 4:04 pm   #24
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Default Re: Hudson help - act 2

Quote:
Originally Posted by sentinel040 View Post
the remains of a sticker with 78.1 and low ba.... scrawled on it.
Ah - we know who its second owner was then...

73,

Colin.
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Old 9th Sep 2020, 6:58 pm   #25
sentinel040
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Default Re: Hudson help

Good evening;

I am sorry, once again, for the delay. I had booked some time off work to enable me to pop back home to undertake some jobs, then a work based panic (lack of planning...) thew life into freefall.

So, what do I know, well I went around all the tuned citcuits and for reference I have posted (if I have got things right!) a copy of part of the circuit to assist in understanding what is where. If you can read it.

As mentioned there is a receive crystal for 70.26MHz fitted and using the aged 2950 test set the front end is tweaked up as best it can; but is still very deaf. The Altai GDO calibration is a little out, 70.26 shows up as circa 70.5. i did not check the calibration on the other frequencies. Below is a list of the outcomes, after a bit of a battle to get close to some of the tuned circuits, the figures in brackets are what it should be.

The first local oscillator multiplier chain: -
L20 - 14.6 (14.89)
L21 - 33 (29.78)
L22 - as above
L23 68 (56.56) Not good.

Then turning to the front end tuned circuits, all should be 70.5 (the GDO's reading for 70.26): -
L12/13 - 80 Not good
L14 - 70.6
L15/16 - 70.5
L17 - 70.6
L18 - 70.6

So the errant tuned circuits are the aerial input (L12/13) and the final first LO multiplier, L23.

I have had no time to go further and i am away again in carer mode for a few weeks. Its a bit too big to have come with me....

Cheers, and thank you.

Ian
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Old 10th Sep 2020, 9:51 pm   #26
Peter F4VSA
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Default Re: Hudson help

I have an old Hudson radio, not sure which one. AM, transistor receiver, valve transmitter. I will have a look at it to see if there are any crystals in it, it is high band

Peter G8BZR/F4VSA
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Old 12th Sep 2020, 11:39 am   #27
sentinel040
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Default Re: Hudson help

Thank you!

Ian
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Old 13th Sep 2020, 10:27 am   #28
Jon_G4MDC
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Default Re: Hudson help

Hello Ian - just had a short cogitate on your schematic snippet.

About L23 which doesn't seem to have tuned correctly, I suppose the decoupling capacitor at the top of the inductor is all present and correct? After that you could try adding some extra capacity to the tuning capacitor that goes to ground. Probably in the order of 5-10pF would be good but it needs to be well able to stand HT Voltage. 50V Ceramics definitely won't do!

On the 1st RF Stage Input filter there is a capacitive tap across L13 but then another shunt capacitor which might be fitted / not fitted depending if you are working at the top or bottom end of the band maybe? Again I would try adding about the same amount of C here and checking the resonance again.

Hopefully you can pad both of these coils so they tune through the wanted frequency at the mid point of the adjustment range.

Good luck - hope you get some time to work on it.

I forgot to add - I like the shorting relay for selection of crystals Ch1/Ch2!
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Old 17th Sep 2020, 8:31 pm   #29
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Default Re: Hudson help

It's likely to be a few more weeks until I get to the radio again, but will have a look at those tuned circuits then, well at least one of them!

The actual crystal switching is different, as the radio now has three channels with a front panel selection switch, which whilst apparently professionally done complete with engraved label, odly only actually has one channel with the wiring completed. The additional two crystal holders being were the relay was.

I will be in touch, honest!

Ian
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Old 18th Sep 2020, 8:54 am   #30
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Default Re: Hudson help

Not a problem. Life gets in the way of hobby - it's normal.
Interesting info on the crystal switching. I wondered if the relay version was maybe related to a remote mount version with cable and control box.

Pye Cambridge used Ledex switches to overcome that problem.
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Old 18th Sep 2020, 6:48 pm   #31
Peter F4VSA
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Default Re: Hudson help

Hi all, I've found my Hudson under a pile of work in progress, or junk as the wife calls it. It's an FM208, transistor receiver and valve transmitter. The transmit crystal is 4482.18Kc/s and looks to be times 16 to get to the final frequency. The receive is 9334.37Kc/s. The first IF is 10.7 with a 10.25Mc/s to get to the second IF. Very much like the Pye equipment. There is a times 8 chain on receive.

I have no idea why I bought the unit, just felt sorry for it. I'm happy to give it away for the cost of postage but it is in France at the moment. It's almost complete, all of the tx and rx strips and power supply. Pictures available if anyone is interested.

Peter F4VSA
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Old 20th Sep 2020, 9:42 am   #32
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Default Re: Hudson help

It's in nice condition. Looks like it could be high band 140MHz rather than 70MHz?
Only guessing mind...
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Old 16th Oct 2020, 3:55 pm   #33
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Default Re: Hudson help

Well, I finally managed to find time from my caring duties to have a further look. All of the coils did have double peaks, just. That is the key trap I fell into, the peaks were rather close together. Also as mentioned before when I looked with a "GDO", the actual resonance of them was still off. Armed with a mixture of HV and LV ceramic caps I managed to spread out the double peaks with the result that instead of just detecting a 30 microvolt modulated signal it now just detects a 1 microvolt modulated signal. The final LO and first RF tuned circuits were by far the worst culprits.

Now to start to look at the TX, which refused to oscillate. Pop the RX crystal in and off it went, the TX oscillator that is. Put the 8.7825 MHz (x8 for 70.26) HC6U TX rock back again and nothing. By the way, the radio originally had FT243(?) holders, but I replaced one pair. I put both of the second hand crystals (from a reputable known source) into the "GDO" to test them and both oscillated. Hmmm. whilst having a prod around, as you do, I found that if I gripped the anode tag of the valve holder with a small (insulated!) pair of pointed nose pliers the oscillator burst into life. Remove said pliers and it died again. The same with a diode probe, which is what started me proding around. Ok, lets try another ECC82, or two. There was a difference in amplitude and in one case once started, with the pliers, it would continue once they were removed. Then I turned the radio off (I swopped the valves with it running) and next time it would not do the same; typical. Out of interest, I did try a few small capacitors including a "gimmick" of a few turns of twisted wire in various places to see what would happen. The simple answer being not a lot!

I fitted an small HC25U crystal for 8.785 MHz and that sang merrily. So, having oscillation I went through tweaking things using a scope, (the poor copy of a manual I have does not give typical readings) until I came to the driver anode /PA grid tuned circuits, when there was a sudden jump in output level. Hmmm, I think I know what that might be, and sure enough shorting the crystal out had no effect on the signal, the QQV0-310 PA seemed to be making its own oscillator. Not a lot of output, the power meter on the old 2950 test set was only just moving off the end stop, but that is not the point. Changing the '310 did not change anything else. In fact, the waveforms of the signal going through did not seem very clean to me. There was no audio being fed to the modulator by the way.

I have attached a few images taken off the scope, apologies for being a Muppet and forgetting to turn the scale illumination on until the last one. All bar the PA taken with a non-Tek x10 probe at .5V/div; the PA anode being taken at .1V/div and g1 at .05V/div. The timebase was set at 0.05 microseconds/div.

As at this stage the file upload seems to have stripped the names off the images, in order, they are:-
First multiplier anode.
Second multiplier g1.
Second multiplier anode.
PA g1
PA anode.
It will now probably put them back when I post this, just to show me up.

At this point I ran out of time, for the moment. But rest assured, I will be back, when I can get to the radio again.

73

Ian G8KSZ
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Old 17th Oct 2020, 9:59 am   #34
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Default Re: Hudson help

Strange behaviour from that crystal oscillator. Is there any chance to post the circuit of the TX one? It's probably similar to the RX higher up the thread but it would be good to know.

I wonder if you have a sleepy crystal? They are not unknown. Impurities settle on the plate and reduce the activity so that an oscillator with little feedback can't start them. If you add a good transient eg with your pliers they start and maintain.

If it's a hermetically sealed type e.g. HC6/U there's not much you can do. With an FT243 you might dismantle and clean the plate. I have had some success at reviving sealed ones by giving them a good kick up the backside.

Get an 8MHz signal generator with a decent output level of +10dBm or so and connect it across the crystal with a 10ohm series resistor on the hot side. Connect the scope across the crystal. Fine tune the signal generator until you see minimum Voltage which is when the crystal is series resonant and accepting all the power. Leave it for a good while. They can go back to sleep again but I have known it to work.
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Old 18th Oct 2020, 9:22 am   #35
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Default Re: Hudson help

Jon;

Thank you for the input. I had not heard, or if I had I had forgotten about it, of the sig gen trick. I will try that when I get home again. Its odd they both seem to "go" in the GDO, I assume it is down to the circuit differences and this is what threw me at first.

The Tx Osc circuit is attached. Well the one from the manual is. At some point this radio seems to have been re-worked, it does not look like amateur mod's. They include a squelch circuit, which I will return to in a minute, and the channel selection. First the crystals, the relay has been removed, or not fitted, and a pair of additional crystal holders fitted to make it three channel. All the trimmers are the same and have the same colour locking paint on them, which in turn is the same as the rest of the radio. On the front panel, a rotary channel switch had been fitted along with the squelch control and an engraved plate behind them and the existing volume control. All the period knobs match. The switch has been fully wired, after the style of the relay switching circuit, but goes nowhere; on both transmit and receive a single crystal holder has been nicely wired directly to the valve in question. With regard to the transmit crystal the series 100pf capacitor has been omitted. I did try to add it back again but it seemed to make no difference with the original "faulty" / low activity crystal.

Returning to the squelch circuit, at the moment it seems about as useful as a bicycle to a fish as once it closes it takes about 20-30 microvolts to get it to open again; which is rather a wide hysteresis. This is not shown on the circuit diagram I have and I think I may have to sit down and trace it out. I expect it to be to derived from the AGC line somehow, but at this stage all bets are on.

73

Ian
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Old 18th Oct 2020, 9:42 am   #36
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Default Re: Hudson help

Hello Ian, that's a Colpitts. Strange they have taken output from the Anode, as many do, but it's a necessary condition for oscillation that the anode is decoupled - see C16. I wonder what value that is?

They obviously aren't trying to multiply in this osc, unlike the RX one with a tuned circuit on the anode. (That one oscillates since the parallel tuned circuit is Low Z at crystal fundamental frequency)

If you make C16 large (put 2200 or 4700 pF in parallel for a quick test) does it oscillate then? There probably won't be enough drive because you have shunted it all away but if it does oscillate then I wonder could you feed the second triode from the cathode instead. There should be plenty of go there.

It will be a balance for the value of C16 between oscillation and drive level with the circuit as it is. This could be why the pliers worked..

The squelch doesn't sound like a great device as yet! Hopefully it can be improved or if you have a quiet location maybe you can do without it. I quite like listening for thunderstorms which 4m is particularly good for.

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Old 18th Oct 2020, 10:33 am   #37
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Default Re: Hudson help

Good morning Jon;

That was quick! The one thing I forgot to mention is that C16 is not there and there is no sign of it ever having been fitted (like the capacitor betwen the crystal and the grid). I noticed that because I was curious as to its value after discovering holding onto the anode pin with a small pair of pointed nose pliers made it oscillate.

As an aside, all the higher value little brown Hunts capacitors with cracking cases have been replaced as originally the inverter struggled to start up due to the load imposed by all the leakage, as as they were replaced, one at a time, each time I tried it the inverter pitch was higher.

The odd thing is that it does oscillate with the small HC25U crystal temporarily hung in (the hot side soldered and the earthy side connected with a croc clip lead). The radio has certainly seen a lot of use, judging by the sweaty nature of many of the components and general heat and dirt marks on the chassis, so it must have worked in some form and whilst the actual radio does not match the circuit and had oddities, it seems unmolested, a bit of a curious one that, which will probably never be resolved.

I agree the squelch is a nice to have, but given it seems to be professionally fitted, I would have expected it to operate professionally as well!

It is likely to be a few weeks until I can get at the radio again so there might be a slight lull.

I have included a picture of the transmit oscillator section of the chassis, not that is really shows much of interest.

73

Ian
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Old 18th Oct 2020, 10:42 am   #38
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Default Re: Hudson help

Lots of beehive trimmers - thats interesting!

You have probably nailed it there Ian. I reckon that oscillator is not going to be very willing to start without some decoupling on the anode. It's fussy and will only go with the most active crystals.

Maybe you can add some capacity where C16 would be, just enough it will reliably start, and maybe the output drive level will still be enough. I much prefer to take drive from the Cathode on a Colpitts and to properly decouple the Anode. I'm not sure why they would do it the way they have.

Good luck with it.
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Old 18th Oct 2020, 11:45 am   #39
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Default Re: Hudson help

The other beehive trimmers with HT on them in the driver and pa anode circuits are more "interesting" to adjust! Turn with an insulated trimming tool pressing on the edge and they wobble on their axis, so when any pressure is removed the resonance changes.

What sort of value of anode de-coupling would you suggest? I think I tried a low value one with no effect, inclding a gimmick of a few turns of wire. I did not try too high a value in case it did load it down too much.

I was initially impressed with the way the radio was built, but I am now starting to wonder about the quality of the actual RF design!

Then there is the matter of why does the PA take off on its own? I suppose one step at a time!

Take care, I will let you know in due course.

Ian.
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Old 18th Oct 2020, 12:15 pm   #40
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Default Re: Hudson help

10pF is where I would probably start but wouldn't be surprised if it needed 22pF or more.

I think the gimmick would be too little capacity. It's hard to get much more than 1-2pF that way.

If the coupling capacitor on the grid of the second triode will reach the cathode instead of the anode then trying a big decoupler on the anode would also be worthwhile. 100pF or more. It depends what you have that is good for the Voltage.

I see Pye used a Pentode as a Colpitts oscillator in the Cambridge TX design. I wondered if the Anode tuned circuit was used as a multiplier but it isn't. The output is x1 in all frequency variants. This circuit is sometimes called electron coupled since it's the screen grid which is acting as anode in the oscillator part. You can see that is decoupled by 1nF.
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