Date: 16 Oct 89 13:29:08 GMT From: philmtl!philabs!briar.philips.com!rfc@uunet.uu.net (Robert Subject: some IC37 mods Msg# TSP Size #Rd Date/Time MsgID From To 6051 BF 2985 0 1010/0541 1631_N2EYR W2JIA ALL@ALLBBS Sb: IC37 mods. Here is a list, transcribed from "220 Notes", of modifications for the ICOM model IC-37A. The 27A and 47A should be very similar: "We have been using [this mod sheet] in the Southwest Coast ever since the [IC-]'37 was in production. This one is the latest revision. "The design problems of the '37 are greater than ICOM would lead you to believe. The [IC-]'38 has solved a great majority of the '37a problems. However, the microphone and the UHF pigtail problems still remain. "The fix for the microphone on both rigs is the same. [see below] The fix for the UHF pigtail on the '38 involves removing the pigtail, and installing a bulkhead chassis mount BNC connector in the hole left by the pigtail assembly. Some elongation of the BNC connector holes is necessary for a good fit. A short coaxial jumper may then be installed from the board to the connector. "Now, here is the official Condor Connection IC-37 modification sheet. "1. To restore high-frequency receiver audio response, replace C-103 on the main unit with a .0022 uf mylar capacitor (that's 2200 pf). "2. To restore LOW-frequency receiver audio response, replace C-106 with a .22 uf mylar capacitor. "3. To eliminate the distortion in the transmit audio, install a 4.7k ohm resistor inside the microphone case, in series with the white lead coming from microphone element. Once the resistor is installed, set the DTMF level pot to the middle of its range (this pot is the only one inside the microphone case). To complete the mod, set R88 inside the radio to the desired "mike" level. "4. To improve the receiver sensitivity, power output, SWR at the radio, and reliability, remove the RG-58 pigtail and the UHF connector extending from the rear of the radio. Install a BNC chassis mount, screw-in connector (UG-1094/U) in the hole left in the back of the radio. The new connector will screw in as if the modification was done at the factory. "5. To greatly reduce chassis heating in the receive mode, remove the following components: R66, R67, R68, Q32, D42, and D44 in the main unit. Install a 7808 [3-pin voltage regulator] on the transmitter power amp shield behind the space reserved for the optional voice synthesiser. Thermal compound is recommended. Hook the input of the 7808 to the point where R67 and R68 used to connect. Hook the output of the 7808, in series with a 1N4001 diode, to J14-1. The cathode of the diode goes to the connector goes to the connector, and the anode goes to the 7808. "---Mark Gilmore, WB6RHQ Newbury Park, CA." One note on the above - the BNC connector mentioned for the x7-series radios is sold by Radio Shack as 278-105, $1.39 each. Note: I haven't tried these, proceed at your own risk. WA2ISE 0158z, 1390 msgs, #6500 last @KD6TH-4 MailBox>