Heil HC104
iCOM Installation Instructions
Please be aware that the early model 'zero' iCOM rigs (720, 730 and 740) do NOT have a mic preamp on board. It was built into the hand mic so you can not use a microphone element straight into these inputs.
The 735 model has minimal preamp (-10 dB short in gain). Use the compressor on at a low level, which then acts as a preamp and the dynamic HC element should work.
iCOM pro models: On these models iCOM raised the standard preamp level, so gain might have to be run up to about 2 or 3 o'clock. Check the ALC meter for proper deflection.
Enclosed in this package is the d.c. blocking capacitor, which must be used in series with the hot lead of the microphone, so the d.c. phantom voltage on all iCOM rigs does not get to this dynamic element. This is a polarized capacitor so + goes to radio.
XT-1: Lo to Hi-Z Transformer
The sub miniature audio input transformer from Heil Sound is ideally suited for matching low impedance microphones to high impedance inputs found in vacuum tube transmitters (Heath, Collins, Drake, etc.)
The XT-1 transformer is small enough to be mounted inside a microphone housing, some headsets or mounted in a small metal box with appropriate connectors to mate with your microphone and transmitter.
- Input Z 1,000 ohms primary white/black
- Output Z 30,000 ohms secondary red/yellow
- Frequency Response: 50 Hz -16 kHz @ -3 dB
Key Element Engineering Specifications
The Heil HC-4 and HC-5 were designed in 1983 to solve the problem of mushy, bassy SSB audio. The dynamic elements use copper wire wound bobbin voice coils. The diaphrams are uniquely tuned by a labryinth that is made up of an inch and a hlf of 3/32" copper tubing. It is this tuned tube mounted at the center of the voice coil that gives the opportunity to tune each of these elements with it's specific audio peaks.
The -3 dB points of the HC-5 are set at 300 Hz and 5,000 Hz with the tuned peak being +6 dB centered at 2,000 Hz. The -3dB points of the HC-4 are set at -600 Hz and 6,000 Hz with the tuned peak being at +10 dB centered at 2,000 Hz.
Both of these peaks are right in the middle of the Fletcher Muson Curve (or equal loudness) of the the human ear. This curve discovered by Bell Labs in the early 1930's shows that the human hearing has a tremendous loss centered at 2,000 Hz and is very dependent on the volume level of the signal. Heil sound built these special microphone elements to equalize the losses of those all important voice frequencies and bring them back to an articulate level and above (perfect for SSB transmissions.)
- Impedance: 1,000 ohm @ 1 kHz
- Dimensions: .530" x .850" x .310".
- Sensitivity: HC-4 is -66 dB. HC-5 is -68 dB.
These dynamic elements are designed to be close talked (within 1-2 inches).
Instructions:
- Remove the original crystal element and install the foam screen and adhesive backed acoustic pad.
- Cut blue foam (from inside the box) in circle to fit inside of microphone.
- Place the HC element facing inward on the blue foam being very careful when soldering the small p.c. pads on the element.
- Cut the piece of blue foam from the inside of the box so it holds the element secure to the front grill and replace the back cover.
Contents:
- blue foam
- black foam with adhesive circle
- XT-1 (for high impedence applications)
- cap (for iCOM rigs)
