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Old 7th Jan 2013, 8:25 am   #1
saposoft
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Default DORAM Distortion Meter circa 1975

Hi everybody,

A fellow of mine has found this instrumen. Used to work, it was used to test distortion while designing audio power amp, manufactured circa 1975.
No other info.
Looking for information about it, how to use it, possibly a manual.

Thanks a lot.
Alessandro
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Old 7th Jan 2013, 11:01 am   #2
G0HFCFrank
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Default Re: DORAM Distortion Meter circa 1975

A quick google found

http://www.epemag.wimborne.co.uk/history2.htm

It appears DORAM was part of RS
"DORAM Ltd. (the Doorway to Amateur Electronics) traded as the amateur's offshoot of RS Components Ltd, but was later closed down. RS later launched Electromail instead, based on the RS catalogue."
Perhaps RS may have some record of your distortion meter?

Frank C.
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Old 7th Jan 2013, 11:01 am   #3
Radio Wrangler
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Default Re: DORAM Distortion Meter circa 1975

Doram was a company in Leeds selling electronic components to the public, and also selling a number of kits. I remember them seeming to have high prices.

They were owned by RS Components Ltd (previously called Radiospares Ltd)

At that time RS were the most comprehensive catalogue firm for components. Their stuff was expensive (and still is) but they are notorious for only dealing with trade account holders. By the time their components were marked-up for retail sale, they were definitely overpriced. Doram didn't seem to last for long. Leeds was and is also the home base for RS's greatest rival, Farnell. Farnell were usually a bit cheaper and they were/are happy to sell to anyone. I'm surprised Doram lasted at all.

Your photo is the first bit of Doram equipment I've seen in 30+ years.

Good luck on the manual hunt!
The people on this group have surprised me many times.

David
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Old 3rd Mar 2014, 11:35 am   #4
Labmik58
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Default Re: DORAM Distortion Meter circa 1975

Quote:
Originally Posted by saposoft View Post
A fellow of mine has found this instrumen. Used to work, it was used to test distortion while designing audio power amp, manufactured circa 1975.
No other info. Looking for information about it, how to use it, possibly a manual.
I have just picked up in a local University Auction in Brisbane, Australia, where I live - the Low Distortion Audio Oscillator made by Doram. This unit is in very good condition for its age and needs minor servicing. In searching for technical information about it, I found this website / forum.

It runs sine and square wave outputs from around 9Hz through to 100 Khz up to 3 volts p-pk on sine and 10 v p-pk on squarewave.

Upon opening the rear panel, I could tell is was a very nice early/mid 70's build with Radio-Spares quality 240 volt / 115 volt power transformer ( 3 VA in size ) and a thermistor stabilized Audio Oscillator; with a Power Supply and metering PCB. 3 boards in all.

All parts were neatly laid out and well marked. The only thing missing on my unit was two of the small stick-on rubber feet - easy fix.

I would appreciate anyone who might be able to assist with tech data, a schematic diagram, or service manual for the unit. My application is for testing Vacuum Tube audio gear.

If anyone has the matching Audio Distortion Meter they want to part with, for me to match up, I would be most interested.

Kimbal.

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Old 4th Mar 2014, 2:31 am   #5
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Default Re: DORAM Distortion Meter circa 1975

They were badly overpriced and were selling into a market where people compared specs and prices quite carefully.

Your oscillator will work with any other make of distortion meter. You'll find them by Heathkit, Levell, Lyons, Ferrograph, Radford, Tektronix and HP.

The Radford ones are rather sought after (and their low distortion oscillator) HP did several models including ones which would automatically follow your tone around with their notch.
(HP 8903)

David
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