What is perceived better radio, the Larkspur R209 or the R210?

[AdrianH]

I know the question may be vague, but I am interested in getting an old military receiver of some description. A long time ago, I used to have the R210 and even with the humming vibrator thought the unit was OK, sensitive for what I needed could pull in week signals and could resolve SSB.

I can not remember what it was like for bandwidth on broadcast stations as I am talking probably 30 to 40 years ago. There seems to be some R209 around at the moment which is unknown to me, I can see it will go to 20 MHz which is higher than the r210, but would appreciate others thoughts on the radios, regards sensitivity, bandwidth etc. and general preference.

I have simple SDR's and an old FT-70 that I can play with but I seem to miss the twiddling of a knob to go up and down the band.

Cheers

Adrian

[G6Tanuki]

I've got a couple of R209Mk.II here - had them for 40+ years, one of them I took with me when I went to University and it served me well as a HF receiver [I regularly got mentioned in Practical Wireless's Amateur Bands column...]

Like all general-coverage receivers the tuning-rate is severely less-than-ideal for tuning SSB - you soon develop what a friend described as "a safecracker's touch" - but the 209 is good-enough for general listening even if the IF bandwidth is rather wide by modern standards. [Hint: disconnect the R:C feedback filter in the audio output-stage - this is by default switched-in when the function-control is set to 'CW' to activate the BFO. It may make sense for CW reception but it's not a help for SSB].

Absolute sensitivity doesn't matter on the HF bands these days: the background noise-floor is so high!

I've replaced the vibrators on mine with a solid-state version: two TIP3055 transistors, 4 resistors, 4 Zener-diodes. Saves 400mA of 12VDC power, and no more annoying hum!

If you are looking at a R210 be aware that the 'filmstrip' tuning-scales do not age well; I know a couple of 210-owners who picked up receivers cheaply because of this, and found it wonderfully-easy to fit a sub-10-quid Chinese frequency-counter/display rather than messing around with mechanics and filmstrips.

[AdrianH]

Thanks for the response, am I correct in thinking the 209 MK2 can operate from mains?

Adrian

[G6Tanuki]

No the 209Mk.II is 12V only.

Can't remember if it was the Mk.I or Mk.III that was mains-able.

The 12V-only versions - whatever you do, don't operate them from anything more than 13V [for example a 12V battery being 'float charged' or powered from a car-battery while you're actually driving the car] - the poor little 1.4V battery-valves are fed from the +12V supply via simple series-dropper resistors - if you give the receiver too high a voltage the filaments get over-run and lose emission - first symptom of this being when the LO stops oscillating at the top end of Range 4.

[AdrianH]

OK I will have another look for manuals, I may be getting confused as I downloaded a manual from VMARS for the R209/2/B and assumed obviously wrong this meant mark 2.

Thanks.

Adrian

[AdrianH]

It looks as though the R209/2/B is a Dutch version and can be mains powered directly as well as 12/24 Volts.

Was there a list of modifications typically done by amateurs, I am not after keeping one as original, I want to use it to the best it will.

Adrian

[G6Tanuki]

I've never come across any sort of list-of-mods for the 209; the only 'major' change I did on my ones was to re-wire the BFO HT-supply to come from the voltage-regulator valve that feeds the local-oscillator. This slightly improves the BFO's frequency-stability - otherwise it can shift by a couple of hundred Hertz as you adjust the gain control.

If you buy a 209, expect to have to 'do something' with the vibrator: the can contains a foam-rubber support for the chopper-assembly - after 60+ years the rubber will have deteriorated - and in doing so it releases sulphurous gases [sulphur having been used to vulcanise the rubber] and these will have attacked the chopper-assembly's contacts. Easy thing is to rework the vibrator to a 'Royer Oscillator' using a couple of power-transistors.

Apart from that, the metal-cased capacitors used in the pluggable modules are essentially just posh waxed-paper ones - and we know what happens to these! I replace both the HT-decouplers and the capacitors between the individual filament-dropping resistors and earth with modern 160V yellow Vishay MKT types.

Finally, remember that the 209 has an "IF Out" socket - if you want to experiment, consider feeding this to an outboard IF/demodulator stage - which can be either a product-detector-and-audio-amp or you can go digital and demodulate the IF into I and Q components then feed these into a PC soundcard for some sigital-signal-processing fun!

[AdrianH]

Thanks again, looks like I will get a R209 to play with, just not telling the wife.

Adrian

[AdrianH]

Scratch the last post looks like I have just bought an R210, lets see how well it travels, seems to have had a few extra holes in the front panel for headphones at a guess.

Adrian

[Peter F4VSA]

A good choice. I have owned a couple of R209's but prefer the R210, I now have two of these, the tuning is far superior and they are very reliable in my view

Peter F4VSA

[g4aaw pete]

Good receiver, the R210. I had one for some time, then sold it to another forum member. Mine had a 240v to 12v dc supply that came with it. I believe a company that advertised in practical wireless supplied them at one time.

[AdrianH]

One of my early receivers was an R210 so it would be good to get hold of this one when it arrives. I have already downloaded an article starting in the January 1990 Short Wave magazine on converting one., plus a couple of downloads from the VMARS site.

Think this one will be modified to run with a 24 or 48 Volt AC input, but a lot depends on what state it is in when it turns up. The fact it has a couple of holes in the front of the case may mean, it has some mods already done to it?


If the filmstrip is broken then a retrofit counter module will get fitted, but all for the future.

Amateur radio is loosing appeal with me in general and it is this type of gear (valves in general) that keeps me into radio.

Adrian

[AdrianH]

The R210 has arrived and appears to have little done to it aprts from the two extra sockts on teh font panel of which one was un connected and the other 1/4 Jack socket is connected to the 50 Ohm headphone pin on the main connector.

I now have to decide if I replace this main connector or try to find a suitable female connector to fit it.

Time to play!

Adrian

[AdrianH]

Well how things are moving along. Late morning I started to have a play with the receiver and took a few panels off to have a general poke around. Had the meter out to check for any thing obvious on the power supply and found that two wires were snipped from the main transformer. These were from pins 11 and 13 which supply the HT. measuring the windings one half of the winding was 77 Ohm and the other side 299 Ohms, Checking the capacitors with a simple DVM did not show any shorts or major leakage, but at the output Volts from the DVM I did not expect anything to show. The other windings appeared OK although I was unable to raise the heaters or the -30 Volt line when powered with the vibrator.

Late afternoon, a post in the wanted section had a quick response from Jeremy and I thank him very much for that. I should get a replacement transformer some point next week.

So what to do next! Well a few more measurements, remove the faulty transformer altogether and strap in one of the 6.3 Volt and HT voltage switch mode bucks PSU's, power from 12 Volts and the heaters are all lit, and set the HT output to 175 Volts solder it to a HT line and fingers crossed. The best the PSU can supply is 150 Volts so it must be drawing around 20 + mA, but stick in a pair of headphones and there is noise, the set is capable of receiving signals, plus a lot of noise from the switch mode PSU.

So there is hope things could be OK.

My next step over the next few days will be to look through the circuit and see what the total resistance between Chassis and the HT rail is, then do a quick test without heaters on and see if the HT draw matches what I would expect, if not I will start looking for leaky caps through the receiver.

These things were certainly well built and heavy.

I suspect the Vibrator is suffering from bad contacts as I should have seen some heater supply and -30 Volts during my earlier tests even though there was no HT, but it looks as though one would need to cut the can off to check it out. So I will still head down the idea of putting in either 24 or 48 Volts AC and building the required rectifiers into an Octal plug if possible.

Adrian

[AdrianH]

Have replaced the HT caps in the PSU section all these were showing some leakage when tested to 250 Volts (rated to 350 V) A main culprit was a 0.1uF stuck behind a tag strip. All replaced with modern caps.

Removed a couple of mods that had co-ax attached to the IF section, not sure what was going on with them but the co-ax was floating at the other ends, so not doing a lot.

I found a date on the 100KHz crystal of April 64, so this is younger than I thought it could be, does the serial number plate mean it was a 1964 week 17 manufacturer?







Adrian

[AdrianH]

A transformer arrived from Jeremy today (Pamphonica), so in between household tasks I have been working on the R210.

Finding out more modifications that had been tried and a few more caps that when powered are going short.

The 24 Volt Vibrator was not working so that had the bottom of the can removed to enable a good clean-up of the contacts that had oxidised over years.


There was also two devices that I thought were a type of disc ceramic capacitor at first, that at one time were heading from ground to pins 11 and 13 of the transformer, turned out these are diodes, a type I had not seen before, one is green and the other brown in colour, but no other markings.


I tested them with a DVM which showed they were working, but when I tested them for leakage with 250Volts one broke down and started to conduct the other did not.

The unit was powered up from 25 Volt supply and came into life, a meter in the power lead saying the input current at 1.5 Amps started to rise, not by a great deal up to just under 2 Amps and then dropped again, the set still working.
A 22 Ohm resistor had got hot enough to unsolder itself and drop away, this was R31 a 22 Ohm of a couple of watts, this part of a snubber/buffer circuit to stop the Vibrator contacts arcing and the series caps C116 were drawing increasing current and getting warm and the resistor getting even hotter. They tested OK with a normal DVM but went short at 250 Volts and somewhere in between with the 24 Volts square wave across them. So the caps were replaced with what I had to hand, 4 x 1uF 1000 Volt working units.


So quite a few higher voltage spec caps have gone into the PSU section,not what one would call a original appearance repair, but it is working.

I measured the frequency of the Vibrator unit across the 6.3 Volt winding and got 112 Hz, now what I would like to know is how the transformer would behave with 24 Volts at 50Hz going into it I can imaging that the core is not really suited to that low a frequency? I know that they have been used at 50Hz but imagine a higher current in the transformer windings?

Adrian

[G6Tanuki]

The 'snubber' network across the outer ends of the primary of a vibrator-transformer does indeed need some unusually-high-voltage components: when current is interrupted through one half of the primary-winding most of the energy from the the collapse in magnetic-field in the core -should- be delivered as energy to the secondary, where it provides HT - but some of the energy will be reflected as a high-voltage spike into the primary.

This back-EMF spike can be quite a few hundreds of Volts, even if the primary's only being fed from 12 or 24V. And it has a rather-aggressive energy-profile - so the 'snubber' - whose R-C time-constant really needs to be matched to the L-C resonance of the transformer and the natural frequency of the vibrator - is not a simple thing.

In times-past I replaced the snubber-capacitor on my R209's vibrator-transformer primary with a 250V "safety" Class-X/Y-type - which rapidly degraded-to-uselessness as the back-EMF spikes punched holes in the self-healing-foil dielectric.

[AdrianH]

The original caps were 2 off 2.0 uF metallised cylinders. 250 Volts DC at 70C or 150DC at 85C, so I knew the 1000 Volt ones would do for now, I need to buy some axial 2 uF caps of a similar size all be-it higher voltage, but 2 uF at high voltages seems difficult to get unless I go to Farnell or RS, 2.2 uF is easier but that would not match the circuit.

So the higher voltage caps will do for a while until I can once again build up a requirement for batches of caps to get over the thresholds required.

I have a 40VA 48 Volt transformer on order so I will give that a try as an AC input when it arrives, but I may also just try and rewind a mains transformer to use as an external PSU providing 175 HT -30 and 6.3 Volts, will have to see how i get on with that, but would need to get hold of a correct connector for the power input.

Adrian

[AdrianH]

I had an idea of driving a speaker with the 50 to 150 Ohm headphone output of the R210, getting hold of an old RS universal output transformer just to play with a bit impossible for today.

It is OK going into my stereo headphones as they are 32 Ohm per side so ignoring the common I have 64 Ohms and it drives them well, but a speaker is better for just listening.

So I thought I would try and make a simple audio matching transformer, I aimed at 50 Ohm to 4 Ohm. A turns ratio of 3.5355:1, so 3.5:1 close enough. There is no DC current to consider if I use a transformer across the output of the standard transformer

A circuit description suggests it is only 125 mW output so worked out wire sizes for 250 mW to be safe, 142 primary turns, 40 on the secondary.

I had a scrap small mains transformer, 15 Volts at 100mA so 1VA, I thought this could be OK to try.
My wire size was a bit small for the primary so I did 142 turns, then the secondary at 40 turns then another primary winding at 142 turns and paralleled them together.

I doubt if the R210 was designed for Hi-fi music and I am sure my transformer does not help, but it seems to be reasonable for speach frequencies. No test gear used as yet to check it out.

It passed a few hours on.

Adrian

[G6Tanuki]

Good to hear you're making progress!

125 Milliwatts of audio into a decent speaker can be satisfyingly-loud; plenty of 1960s portable transistor-radios with a couple of OC72 as the output-stage and running off a PP7 battery had that sort of audio power and they were 'loud enough' to arouse the ire of park-keepers and people-on-Brighton-beach back in the day.

Mismatch of impedance is unlikely to cause any damage either: valves are rather rugged [unlike similar-era solid-state amplifiers] and will shrug off mismatch. As you say, it's not going to be hi-fi [the designers of the IF-strip and audio-stages will have slavishly sought to eliminate any signal-components that result in audio output above 3KHz since these play no part in 'combat-grade' audio comms].