Help with IG-72 Audio Generator

[Multi-Volti Devices]

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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