[Amps] Alpha 89

Dick Green dick.green at valley.net
Sun Jan 26 16:00:39 EST 2003

Tom -- The spike is probably caused by the rig's ALC circuit needing time to
settle during the transition from receive to transmit. When you use PTT, you
are giving the rig's ALC circuit time to settle and the spike doesn't occur.
This is a common problem with modern rigs. I once had a TS-950SDX that would
spike as high as 250W! This often caused abnormal gain trips on my 87A (the
fault code was misleading because the firmware checks for abnormal gain
before checking for overdrive.) I see a tiny spike from my FT-1000D -- maybe
100W or so. It's generally only one LED on the 87A's meter. How many lights
do you see? If it's only one or two segments, I wouldn't worry about it.

If you think it's bad that one LED lights in the grid monitor when you hit
PTT without transmitting, you should see my 87A: about four segments flash
and then go out. The first LED in the plate current monitor comes on, too,
and flickers a bit. I can also see a very faint flash in the first six or
seven LEDs in the power output monitor. First, I believe it's normal for a
small amount of plate current to flow when the amp is keyed. This is the
plate idling current. In my opinion, the flash in the grid and output
possibly are caused by the bias voltage settling, but I think it's more
likely that these are anomalies in the 87A's monitoring circuits. If you
look at the detailed schematics, many of the voltages are related. I can't
swear to it, but the LV supply to the op amps in the monitoring circuits
might have a common source with the bias voltage, and could be affected by
the initial bias current draw when the amp is keyed (i.e., the voltage
regulation might not be tight.)

However, and this is the important point, I don't think any power is
actually being output when the rig is keyed with no RF.

Here's another bit of advice: don't use the CW setting. Folks at AlphaPower
told me the amp is designed to run at the higher voltage setting and there's
no point in using the lower setting. Just reduce the drive power if you need
to. I think the switch is there for the days when the FCC measured DC input
instead of output PEP.

Sam -- your problem could be a bad op amp in the grid current monitoring
circuit. I had a similar problem with the first LED in my 87A plate current
monitor. Initially the light glowed faintly and flickered, even when the amp
was in standby. Later on, the light got brighter and the flickering became
very annoying. Finally, the light stayed on steady. The plate current
measuring circuit has no adjustments. With help from the schematics and
voltage measurements I was able to trace the problem to a Motorola MC-1536
dual op amp. A tech at the factory gave me some nominal input and output
voltages that confirmed that the chip was bad. Replacing the chip was a bit
of a problem since it's obsolete. Scott Ehrhorn at AlphaPower managed to
locate a batch and sent me one. As I recall, I had to remove the LV board to
do the repair. After replacing the old chip, the problem disappeared. The
MC-1536 is used in several places in the 87A, and I wouldn't be surprised if
the grid current monitor in the 89 uses the same chip. This particular
problem has no impact on the amp's performance -- it's just an annoyance.

73, Dick WC1M

> -----Original Message-----
> From: S. J. Blackwell [mailto:w5lu at hotmail.com]
> Sent: Saturday, January 25, 2003 1:39 PM
> To: tom at k4nr.org; amps at contesting.com
> Subject: Re: [Amps] Alpha 89
> Tom,
> I have an Alpha 89. I also have noted the first LED of the grid current
> monitor stays lighted faintly.  I have taken care of this by
> ignoring it. I
> have assumed that this represents a maladjustment of the input to the LED
> monitoring ckt, but have been too lazy to do anything about it.
> Sam, W5LU
> >From: "Tom Branch" <tom at k4nr.org>
> >To: <amps at contesting.com>
> >Subject: Re: [Amps] Alpha 89
> >Date: Fri, 24 Jan 2003 18:11:01 -0600
> >
> >I disconnected the rig and just keyed the amplifier.  In CW setting, the
> >grid current first LED glows and then goes out.  In SSB, it
> glows and stays
> >lit.  It's not the IC-746.
> >
> >Tom
> >
> >----- Original Message -----
> >From: "jeff millar" <wa1hco at adelphia.net>
> >To: "Tom Branch" <tom at k4nr.org>
> >Sent: Friday, January 24, 2003 7:27 AM
> >Subject: Re: [Amps] Alpha 89
> >
> >
> > > Didn't I see a lot of reports that these modern solid state rigs have
> > > excessive power in a spike at first turnon, first key,
> etc...depending
> >on
> > > some details of their internal design?
> >
> >
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