Paul -
OK, progress! :-)
The meter circuit is essentially a voltmeter measuring across the shunt
resistor (R36). The "select at test" resistor (R38) is a series
multiplier to convert the mA meter to a voltmeter. Since your 2.2
resistor is "low", you have to decrease R38 to make the "voltme
Thanks for the info on meter Calibration.
Today I put a 6 ohm (closest to 5 that I had) and using .070a x 6 ohm
= .40v at the TP in the B- line. I then removed R38 and replaced it
with a 0-200 ohm trimpot. I got the meter to read on the hash mark
and then measured the pot (about 27 ohms). I the
Paul -
There were at least four different versions of the AC-3.
The first "rare!" version had a filter choke in the 250V supply. It
didn't last very long before Drake realized that a resistor worked good
enough and dropped the extra cost and weight.
The next version (s/n 2501) has the TP.
Wed, 1/13/10, Garey Barrell wrote:
From: Garey Barrell
Subject: Re: [Drakelist] T4Xb meter shunt
To: "Drakelist"
Date: Wednesday, January 13, 2010, 10:13 PM
Paul -
Yes, that was one thing that should have been kept in the
AC-4. The
voltage at the test point shouldn't go over a hal
Garey and Ron
Thanks for the additional info on bias setting. I still have the
cover off the T4 and the AC4 so I need to continure with the meter
calibration/bias setting. The T4 seems to be working well except the
output is a bit low. I am seeing 110W out on 80 and 40M at this
point. The mete
Ron WB4HFN information to post, if he wants,
> when he gets the chance. The modification was more
> difficult to describe accurately than I thought it would
> be. Hopefully the pictures and AC3 schematic will
> help.
> >
> > 73,
> > Ron WD8SBB
> >
> > --- O
ts, when he gets the chance.
The modification was more difficult to describe accurately than I thought it
would be. Hopefully the pictures and AC3 schematic will help.
73,
Ron WD8SBB
--- On Wed, 1/13/10, Garey Barrell wrote:
From: Garey Barrell
Subject: Re: [Drakelist] T4Xb meter shunt
To: "
cation was more difficult to describe accurately than I thought it
would be. Hopefully the pictures and AC3 schematic will help.
73,
Ron WD8SBB
--- On Wed, 1/13/10, Garey Barrell wrote:
> From: Garey Barrell
> Subject: Re: [Drakelist] T4Xb meter shunt
> To: "Drakelist"
>
Paul -
The resistor is ok, but you need to calibrate (with R38) to get the BIAS
setting of 0.07A correct on the meter. Obviously the idle current needs
to be set correctly for linearity. The 1/4W is a little small, but as
long as you keep the final dipped it may be ok. Typical plate curren
Garey
Thanks for the help on this one. The meter shunt on the vertical
board behind the three power resistors was open! Yea...
I replaced it with another 2.2 it is probably too small at 1/4 but it
seems fine for now and I can order a higher wattage one for later.
May still need to get the resist
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