[Heathkit] IM-17 Question - regulated replacement 8.4 VDC. source.

[Kenneth G. Gordon]

On 9 Jan 2007 at 19:29, Richard M. Gillingham wrote:

> Yup!  As I recall, the 8.4 V Mercury cell was used not only as a power
> supply, but as a precision voltage reference for the IM-17.  When the
> manufacture of this cell ceased, the IM-17 became virtually worthless
> except for a collector.

Well...not quite.
 
> Perhaps someone can come up with a practical solution.  IE a regulated
> supply maybe based on a 9v battery??

Although most three-terminal regulators require more "overhead" than a 
9 V battery could provide in this case, there are some that require very 
little such "overhead". However, I don't know of any of those that put 
out 8.4 VDC...yet.

I don't know if the IM-17 has enough physical room inside the case, but 
TWO seriesed 9VDC batteries, and a simple LM-317 adjustable 
regulator circuit WOULD provide all the 8.4VDC energy one needed for 
the IM-17.

As I remember it, the LM-317 needs about 1.5 VDC "overhead" in order 
to work properly. In this case, one would need about 10 VDC to get the 
8.4 VDC one needed for the IM-17. Thus, two series 9VDC batteries, 
18 VDC, would give you both plenty of overhead, and the 8.4 VDC 
would remain until the series batteries' voltage dropped to 10 VDC.

Since the LM-317, as I remember it, is capable of about 1 amp without 
a heat-sink, the entire circuit, exclusive of the batteries, could be built in 
the space of a couple of postage stamps.

Personally, I don't see an insurmountable problem...

Ken Gordon W7EKB