[AMRadio] EICO 720 & 730

[russ dworakowski]

Ron,  you'll  want  to run  less final  plate current.  RCA  specs for
a 6146   calls 110 mils on  the  plate  max.  Modulator  resting  current  
should  be  about 50  to 80 mils.  Russ


>From: "Ron" <ab5wg at mylinuxisp.com>
>Reply-To: amradio at mailman.qth.net
>To: <amradio at mailman.qth.net>
>Subject: RE: [AMRadio] EICO 720 & 730
>Date: Sun, 7 Jul 2002 07:42:23 -0500
>
>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: amradio-admin at mailman.qth.net
>[mailto:amradio-admin at mailman.qth.net]On Behalf Of Donald Chester
>Sent: Sunday, July 07, 2002 1:15 AM
>To: amradio at mailman.qth.net
>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
>
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