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" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: <[email protected]>
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: [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
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