[GreenKeys] Heath HD 3006 "Crossfire"

[Duncan Brown]

/Here is something I wrote a few years ago about the HD-3006 and some 
pictures:/

Here is a picture of a Heath "Crossfire" in action that I have been 
playing with. It is a solid state replacement for a CRT RTTY tuning 
indicator.

There is not much to it, just two LM3915 logarithmic LED drivers and a 
bunch of LEDs. But when I first plugged it in to my ST-6, it didn't do 
anything, so I thought it was dead.

It wasn't dead, just not very sensitive. I think it may have been 
designed for tube-type TUs with lots of output available on the "Scope"  
connections.  The other problem was that the ST-6 has a 1 Meg resistor 
in series with each "Scope" connection, so it gets loaded down if you 
are not driving high impedance scope plates. With the HD-3006 internal 
pots set for maximum, I could only get about half the LEDs to light when 
driven by the ST-6.

Heath put in a diode detector to rectify the M & S tones going into the 
LM3915, but it is not really needed, as there is a detector in the 
LM3915.  So I bypassed D21 & D22 and removed C4 & C5. I also removed R2 
& R5 (180K across the input). With the HD-3006 internal pots at max, the 
ST-6 can now just barely drive the LEDs to maximum.

When receiving ITTY off the Internet, you don't need any tuning, so the 
HD-3006 isn't necessary. But when receiving off the air, it makes tuning 
the radio much easier than using the ST-6  "++ Meter."

Have fun,

Duncan
K2OEQ
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