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Old 19th Jun 2020, 11:22 am   #1
jimscoper
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Default R210 Larkspur receiver power supply

I have one of these and it works pretty well - but.

Power supply is a 6 volt transformer feeding up the power cable to the normal internal transformer, a previous owner has fitted diodes to derive the HT. The vibrator is present but not used in this mode.

This works all right but hums. Previous owner has fitted extra choke/electrolytics presumably in an attempt to control the hum.

Any advice, either to attempt to keep the existing 50Hz transformer and try harder to control the hum or to go back to 24 volts DC and the vibrator (or an electronic vibrator).

I did think of a 110Hz 6.3 volt supply but that feels like the wrong way to go.
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Old 20th Jun 2020, 1:35 pm   #2
G8BBZ
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Default Re: R210 Larkspur receiver power supply

Hi,
Backfeeding 6.3v AC into the heater winding on the vibrator transformer was a popular way of converting the R210 to mains operation in the past. John's Radio in in West Yorkshire used to sell R210's already modified this way - maybe you have one of these.
As the original heater supply was AC - admittedly at 100Hz or so rather than 50Hz - it would seem that the hum is not caused by the use of an external AC supply but because of something in the set.
As you have the vibrator, it may be worth temporarily applying 24v Dc to the power input so that the set operates off the vibrator system to see if the hum is still present. If it is then it would seem to confirm a problem in the set.
The solid state vibrators (like those from the 19 Set site) are very good and if you have a suitable source of 24v DC I would recommend getting one of those and operating the set as it was designed to be - after you have tracked down the source of the hum perhaps.
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Old 20th Jun 2020, 8:15 pm   #3
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Default Re: R210 Larkspur receiver power supply

I've just retrieved my R210 from the garage shelf where it's lain forlorn for 20+ years.

I got it from Anchor Supplies in Nottingham a long time ago.

It came to life immediately on the 6v transformer I had wired in.

As you see it, it's receiving China Radio International on a meter-probe aerial.

With the volume turned down to near zero, if I put my ear to the LS I can hear some 100Hz hum, but to be honest I would have expected that, especially with the "hi-fi" car door speaker I am using. (regular "Big Clive" viewers may recognise the speaker connector).

I used to use a small radio-telephone loudspeaker that had little bass response, but I can't find it to try.

Perhaps your LS or cans are just too good!

PS Welcome to the forum Jim!
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Old 21st Jun 2020, 8:27 am   #4
jimscoper
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Default Re: R210 Larkspur receiver power supply

Thanks for the replies. Rambo may have pointed me in the direction. When I got this RX it had heater and phone wires poking out through a hole drilled in the case (no plug). I had a lathe at the time and turned up/bodged a plug. I used caravan cable to carry heater and phone leads. I suspect that because these wires are not twisted or mutually screened I could be getting pickup from heater to phones. Will check later on.

One question to Rambo, how are you matching the output to the speaker - a replacement O/P transformer or special speaker...

Rgrds
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Old 21st Jun 2020, 9:58 pm   #5
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Default Re: R210 Larkspur receiver power supply

Quote:
Originally Posted by jimscoper View Post
Thanks for the replies. Rambo may have pointed me in the direction. When I got this RX it had heater and phone wires poking out through a hole drilled in the case (no plug). I had a lathe at the time and turned up/bodged a plug. I used caravan cable to carry heater and phone leads. I suspect that because these wires are not twisted or mutually screened I could be getting pickup from heater to phones. Will check later on.
I doubt it somehow, given the short run and low impedance.
Quote:
Originally Posted by jimscoper View Post
One question to Rambo, how are you matching the output to the speaker - a replacement O/P transformer or special speaker...
Now that would explain the lowish volume, and the distortion when I turn it up near max, the speaker I'm using is 4 ohms
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I cant quite see what that says, 30-50 Ohms? Quite a mismatch.

Perhaps a 15 Ohm speaker wouldn't be too bad.
An easy option would be to use a modern active speaker, perhaps with a couple of resistors or a pot to attenuate the input.
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Old 22nd Jun 2020, 1:53 pm   #6
jimscoper
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Default Re: R210 Larkspur receiver power supply

Hi All,

I tried separating out the phone leads - no real difference. More to look into there.

Also tried a loudspeaker but used a 110 - 15 volt mains transformer as an audio match - this works very well. About 5 - 1 voltage ratio would match 3 ohms to 75 which should suit the phones output. The 100 - 15 is a little too high and using 240 - 15 is certainly worse performance. A 75 volt to 15 volt transformer would be better but nothing like that in my junk box. But no noticeable hum on this setup. Will take another look at my phones.....
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Old 24th Jun 2020, 11:45 pm   #7
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Default Re: R210 Larkspur receiver power supply

Would a Clansman speaker not be about right? I'm sure they're comparatively high impedance.

73,

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Old 27th Jun 2020, 9:43 am   #8
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Default Re: R210 Larkspur receiver power supply

Hi jimscoper and others,
I have a series of 3 articles written by TomHarrison GM3NHQ in Shortwave Magazine Jan 1990 extolling the virtues of converting this unit and giving conversion details.
Quite happy to scan and send to you. PM if interested

John
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Old 27th Jun 2020, 9:47 am   #9
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Default Re: R210 Larkspur receiver power supply

'Computer speaker' with a built-in amplifier?

David
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Old 27th Jun 2020, 9:48 am   #10
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Default Re: R210 Larkspur receiver power supply

Just to save John some time there is a copy of the magazine in pdf format here
https://worldradiohistory.com/UK/Sho...WM-1990-01.pdf

The world of history site holds many magazines.

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Old 27th Jun 2020, 9:56 am   #11
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Default Re: R210 Larkspur receiver power supply

D'oh. I had forgotten about that website, a fund of all sorts go information
Thanks Adrian.

John
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Old 27th Jun 2020, 10:00 am   #12
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Default Re: R210 Larkspur receiver power supply

I used to own a R210, sometimes wish I still had it, for some reason used the Volnet forecasts on 6.604 a lot to see when the bands were up to go listening around. A set i wish I had kept.

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Old 27th Jun 2020, 11:19 am   #13
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Default Re: R210 Larkspur receiver power supply

When I used R210s I used a 64 ohm speaker directly in place of the headphones. It worked well with adequate sound output.

Jim
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