[volt-nuts] Feedback lamp in Heath Sine-Square Generators

WB6BNQ wb6bnq at cox.net
Thu Sep 2 22:29:44 UTC 2010

Hi Dick,

I am not sure about the Heathkits, but the bulbs used in the old hp-200cd's were the common 3 watt clear nite-light bulb used in millions
of homes.  The basic principal is the changing resistance of the heated wire used to stablize the feedback loop.  You could probably infer
the wattage size from the physical size of the old bulb.

These bulbs also made a great TR relay for low power ham radio use.  I had one set up with my 30 watt input cw trasnsmitter.  The bulb was
tied to the output of the TX and went striaght to the receiver's 600 Ohm input terminals.  When you keyed the TX the bulb would light up
providing about 3000 Ohms of resistance and when cold was quite low in resistance.


Dick Moore wrote:

> Anybody know the type of lamp used for L1, the feedback AGC element in the Heath IG-18, IG-5218, SG-5218 Audio Sine-Square Generators?
> Best,
> Dick Moore
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