Hi Don: Thank you for the information on your station. It sounds as if you have taken the modulator to the limit and I hope to hear you on the air on AM some day soon. I am sure it really sounds good!
I do have one question on using the 720/30 pair together. That has to do with loading up the 720. Do you load the 720 to about 120-150 ma final current and then switch in the modulator. What is the resting plate current on the 720 when it is on the air? I am about to finish a restoration on the 730 modulator and put it on the air with the 720 and do not want to "over drive" the transmitter. Thanks, Ron, AB5WG -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Donald Chester Sent: Sunday, July 07, 2002 1:15 AM To: [email protected] Subject: Re: [AMRadio] EICO 720 & 730 I use a 720/730 on 10 m. I feed the 720 on 40m. using a digital vfo. There are no substantial mods to the 720, other than PTT and replacement of a burnt-out power transformer. I made the following modifications to the 730: (1) I removed the clipper stage and its associated components. (2) I installed a 40 hy 120 mill modulation reactor and mounted it in the space where the clipper tube used to be. (3) I disassembled the modulation transformer and restacked the laminations like a power transformer, eliminating the gap in the core. (4) I changed the values of some coupling capacitors, and I recall removing a bypass cap across the mod tranformer (I think). After the mods, it shows flat response from 20 to over 11,000 cps with no visible distortion on the o'scope. I feed audio from the 500 ohm line in my audio rack thru a step attenuator to the "phone patch" input on the back of the modulator, bypassing the low level mic preamp. I changed the mod transformer turns ratio tap to give the least amount of stepdown, therefore improving the positive peak capability. I wired up a PTT circuit that works off the same 28 vdc relay line that controls the rest of the station. I always get good reports on the signal quality when the band is open. I use a simple quarter wave ground plane with 3 drooping radials. Don K4KYV _________________________________________________________________ Join the worlds largest e-mail service with MSN Hotmail. http://www.hotmail.com _______________________________________________ AMRadio mailing list [email protected] http://mailman.qth.net/mailman/listinfo/amradio
