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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 27th Feb 2015, 10:58 pm   #1
G4_Pete
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Default HRO Drift cancelling power supply

HI,
Attached is an overview of the development of a prototype power supply for my HRO. It goes upstream of the HRO power supply with no modifications to the set or its existing power unit. Effectively what it does is stabilise the rms feed to the set as drift is both due to HT and valve heater power. mains voltage here varies 236 to 244 Volts often within a relativly short space of time and causes anoying pitch changes on my HRO. mains voltage form factor in my location is not sine so by voltage I mean true rms.

I had tried to keep it vintage , the technology dates from the dawn of transformers and the 741 op amp is fairly vintage but as you will see I had to put in one modern rms chip to make it work.

However I have reached a wall now and am running out of energy on this project so I will throw it to the wolves and see what comments there are before moving on!

Pete
Attached Files
File Type: pdf AC Mains rms regulator.pdf (1.10 MB, 291 views)
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Old 27th Feb 2015, 11:32 pm   #2
Bazz4CQJ
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Default Re: HRO Drift cancelling power supply

I wonder what you mean under the term 'drift'? When listening to CW or SSB on the standard HRO, I found that there could be an effect I would refer to as 'chirp', not so much a drift effect as a instability effect. I found I could eliminate that simply by putting in a neon stabiliser tube, decoupled by some suitable resistance and a cap to supply the HT just to the local oscillator and BFO. With that in place, I never had any problem in using the standard PSU with regards to any kind of frequency movement.

Pretty much every other comms RX made after the HRO has a stabiliser tube built in as standard.

B
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Old 28th Feb 2015, 12:45 am   #3
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Default Re: HRO Drift cancelling power supply

That's an interesting way to skin this particular cat!

Saturable reactors / magamps are interesting beasts- the stage lighting board at my university used them- a fifties installation that needed a bit of nursing by the seventies and now long gone. It was a bit "slow"- a dead blackout took a couple of seconds- noticeably longer than the normal filament cooldown for the lanterns.
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Old 28th Feb 2015, 9:02 am   #4
G4_Pete
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Default Re: HRO Drift cancelling power supply

Hi B,

By drift I guess I ment the combination of Chirp that you mention, from the short mains fluctuations and slower change that I put down to thermal valve heater effects. And of course the longer warm up drift which is there regardless and quite outside of the scope of what I was trying to achieve.

Yes granted Neon type stabalisers are extensivly used but I guess I started down a path that had excluded retrofitting internal modifications.

From there it became a bit of a crusade to achive a small low wattage stabaliser which became almost secondary to the initial aims of stabalising mains effects on my HRO.

Any way it is presented here out of interest so granted it might not be the simplest solution to a problem but it kept me busy for a few months! (Suffering winter bordom following an active career troubleshooting electronic control systems!!)
Pete.

Last edited by G4_Pete; 28th Feb 2015 at 9:04 am. Reason: Typos - I am certified dyslexic
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Old 28th Feb 2015, 9:45 am   #5
G6Tanuki
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Default Re: HRO Drift cancelling power supply

A fascinating approach to an issue that's all too pervasive in pre-WWII communications receivers.

I wonder - did you consider using the equivalent of a "barretter" to feed the reactance winding? TIn the 1920s there was a design for stabilising the voltage of a wind-driven generator (used to power radios in aircraft) which used a diode with its filament shunted across the output and a slice of the HT the current also passed through the diode fed to a 'bucking' coil on the generator field-coils.

As the generator spun faster its terminal-voltage would rise - lighting the diode-filament more, causing its forward-resistance to drop and so increasing the current fed to the bucking-coil, which reduced the magnetic field in the generator's field-coils so reducing the output...

Think of it as a "thermoelectromagnetic regulator". i wonder if that idea could work on a pair of coupled transformers like you've used?
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Old 28th Feb 2015, 4:10 pm   #6
G4_Pete
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Default Re: HRO Drift cancelling power supply

I did consider using a lamp and a light dependant resistor as the rms detector but had not thought of a "barretter" type of configuration.
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Old 1st Mar 2015, 11:42 pm   #7
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Default Re: HRO Drift cancelling power supply

My HRO came without PSU so I simply built a PSU providing 220V regulated via a 12E1 bottle to provide stable tuning given about 1 Hour warm up.

Very stable.
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Old 2nd Mar 2015, 9:12 am   #8
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Default Re: HRO Drift cancelling power supply

Lamps and LDRs are a lot more available than Barretters.

The ORP12 is still available.

I keep intending using some with ultra-bright LEDs as very low distortion AGC in a receiver I've never got round to building much of...

David
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