[AMRadio] EICO 720 & 730

[russ dworakowski]

Don, I did Steve's mods   to the 730. [WB3HUZ]  I  think its  in  his  
website,  I  always  get  great  audio  rpts  using  my  Eico  730.
As you probably know,  they  did some  great  hi-fi tube  amps  in  the  
50's  and  60's.  Russ.


>From: "Donald Chester" <k4kyv at hotmail.com>
>Reply-To: amradio at mailman.qth.net
>To: amradio at mailman.qth.net
>Subject: Re: [AMRadio] EICO 720 & 730
>Date: Sun, 07 Jul 2002 06:15:24 +0000
>
>
>
>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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