Help with IG-72 Audio Generator

[Terry Perdue]

Actually, it's not in one of the legs of the bridge; it's part of the output
leveling loop. I think that the audio oscillator that was HP's first product
was the first to take advantage of an incandescent bulb's resistance vs
voltage curve in this way.

-----Original Message-----
From: Multi-Volti Devices <multi-volti at softhouse.com>
To: HEATH at LISTSERV.TEMPE.GOV <HEATH at LISTSERV.TEMPE.GOV>
Date: Friday, July 02, 1999 4:53 PM
Subject: Re: Help with IG-72 Audio Generator


>It may be a Wein bridge oscillator. They almost always use an incandescent
>lamp in the bridge...weird but true. I don't remember it's purpose, but it
>definitely will not oscillate with out it...it's a leg of the bridge.
>
>You cannot measure a cold tungsten filament's resistance and get much
>intelligence from the measurement...the resistance is much lower cold than
>hot...that's why inrush current is 'rough' on incandescent lamps.
>
>Murray
>-----Original Message-----
>From: Ed Richards <k6uuz at JUNO.COM>
>To: HEATH at LISTSERV.TEMPE.GOV <HEATH at LISTSERV.TEMPE.GOV>
>Date: Thursday, July 01, 1999 12:31 PM
>Subject: Re: Help with IG-72 Audio Generator
>
>
>>Dave;
>>I am not familiar with that kit, but engineers frequently use a light
>>bulb for regulation as the resistance of the filament varies greatly with
>>the current through it. (measure he resistance of a 100 watt bulb and
>>calculate the wattage according to Ohm's Law! It is not used to emit
>>light, just regulation. It very well could kill the circuit if open.
>>Warning! Use only the original number lamp or the circuit may not work
>>correctly!
>>Ed Richards
>>
>>
>>On Thu, 1 Jul 1999 07:14:28 -0700 Dave <zommbee at IX.NETCOM.COM> writes:
>>>Hello Heathniks,
>>>
>>>I have an IG-72 I'm trying to get working (without the
>>>schematic, of course :-)
>>>
>>>I've recapped it, replaced 1 bad 6X4, but still not
>>>getting it back to life.  There is NOT much to this
>>>thing!  The other tubes test good, and I've tried
>>>substitution as well.  Still zilch.
>>>
>>>But there is a lightbulb on the UNDERSIDE of the
>>>chassis - 110v 3w with a screw-in base.  It's open
>>>and I am getting a new one today.  It's different
>>>from the power light - it's not visible with the case
>>>on and seems to be just a load of some sort.
>>>
>>>What is this bulb used for and if
>>>it's open, will that stop the unit from oscillating?
>>>
>>>Any other ideas on what else could be wrong?
>>>
>>>Thanks,
>>>
>>>Dave WB7AWK
>>>http://www.boatanchors.com
>>>
>>>Sponsored by the City of Tempe
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>>
>>Sponsored by the City of Tempe
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>
>Sponsored by the City of Tempe
>
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