[AMRadio] EICO 720 & 730

[John E. Coleman]

Hi Ron:
	As I recall I used to load mine to about 80-90 ma which I think
was about 60-70 watts input to the plate which gave about 35-40 watts
output on carrier.  I did a lot of experimenting with the modulation
characteristics on 6146s and found that when modulating the Plate and a
screen dropping resistor is supplying screen voltage and screen
modulation that too much modulation is generally present on the screen.
In order to reduce the audio voltage going to the screen, I used a
resistor and electrolytic capacitor in series from the screen to ground.
This bypassed some of the audio but not all and kept the screen voltage
where it needs to be.  I don't remember the values but the resistor was
about 75-80% of the screen dropping resistor so as to reduce the audio
on the screen to 40% when the plate was at 100%.  This really made the
edges of the trapezoid pattern on the scope straight.

As I recall that rig has a clamp tube but none-the-less, I used two
40uf at 450V capacitors in series with equalizing resistor so as to have
the resulting 20uf at 900V just incase the screen voltage should rise high
in a key up mode.

Good luck:  

John, WA5BXO
  

-----Original Message-----
From: amradio-admin at mailman.qth.net
[mailto:amradio-admin at mailman.qth.net] On Behalf Of Ron
Sent: Thursday, July 04, 2002 6:59 PM
To: AMRadio
Subject: [AMRadio] EICO 720 & 730

Anyone on the list using this pair on AM.  If so I would like to
correspond
with you regarding proper loading of the 720 xmtr for AM operation.
Please
send me email and I will respond.

Thanks,

Ron, AB5WG


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