[Hallicrafters] ht-32b audio level

Tue Sep 23 08:14:43 EDT 2003

Ian,

The idea is to drive the final amplifier tubes to the maximum rated output -
no more, unless you want to change the finals more often than the designers
had intended.  Or, even worse, replace the power transformer, which is not
especially robust on these transmitters.  The rated output of the HT-32B is
70-100 W for both SSB (PEP) and CW.  Basically, the transmitter will produce
those outputs into a 50-ohm load if properly aligned.  You might see a bit
more on 80 and 40 and should reach the 70 W on 10.  Also, if your local line
voltage is close to the max input rating (125 VAC), your output may be a bit
higher.

The instruction manual says to set the reference point on the meter to 0 dB
at max CW output, or just a hair less to make sure you are not into
saturation.  You do not have to back off 10 W.  Just back off enough to see
that the power is reduced a bit - that sets the CW level.  Adjust meter
compression to 0 dB at that level.  Modulating to 2/3 of that level on the
meter will result in approximately 70-100 W output PEP due to the damping of
the meter.  See para 4.5 of the manual.  This is the easiest way to operate
the transmitter.  If you drive the meter to the 0 dB level (even if set 10 W
lower than recommended), you WILL be pushing beyond the CW max output and
are probably flat topping.  2/3 (~15 dB on the meter scale) is about right.

You can use a monitor scope to check for flat topping, if you have one
conveniently available.  If so, drive to the point where flat topping
occurs - but if this results in more meter action than approx 2/3 scale,
something is fishy somewhere.  A good peak indicating power meter could also
be used.  A decent non-peak-reading wattmeter will indicate something like
15-20 W on peaks, which is indicating the 70-100 W PEP due to damping.  This
is entirely normal.  The "compression" feature of the HT-32 meter allows it
to kick up higher to the 2/3 point at the same output - allowing you to see
the output with more ease.

Yes, you should ditch the hand mike.  Use a decent high impedance desk mike.
I use a D 104 with good results, but there are plenty of good choices.  The
transmitter does not have built in ALC or other compression circuits.  What
goes in, goes out.  You do have to keep the audio input relative constant -
if you back away too far, your signal will be reduced.  The meter
compression is just that - only the meter itself, not the output.  It was
meant to make it easier to keep the output relatively close to the maximum
ratings.  Just watch the meter when you talk and try to keep the output
PEAKS at the 2/3 level.  The meter will spend most of its time far below
that level.

In any case, trying to pull every last watt out of the transmitter won't
make much difference to the guy listening to you, unless you do overdrive -
and then your signal will spread out in unfortunate ways.  Best to be
conservative and run it the way the manual suggests.  An HT-32B run at these
levels will probably result in many unsolicited compliments on your audio.

Hope this helps.

73,

Rocco N6KN

----- Original Message ----- 
From: "Ian Szekeres" <ian at urbancom.net>
To: <hallicrafters at mailman.qth.net>
Sent: Tuesday, September 23, 2003 7:30 AM
Subject: [Hallicrafters] ht-32b audio level

> Just passed 1 and 3 this weekend, and now that the thrill of my first dx
> contact has passed, I have some questions.
>
> I am having some trouble setting the audio level during ssb tx on my
ht-32b.
> My tuning procedure is as follows:
>
>
> -advance rf level enough to peak driver and final tune
> -continue to advance rf level until diminished advance is noted on the
level
> meter (around 110 watts on my wattmeter)
> -reduce rf level a smidge from this saturation point (resulting in about
100
> watts on wattmeter)
> -using the meter compression control I then set a reference point on the
> level meter
> -switch to ssb
> -adjust audio level so peaks are just tapping the reference level
previously
> set
>
> I have a couple of questions assuming this tuning procedure is ok.
>
> Should I be treating the reference point as a definate do not pass point?
> Setting the audio level this way seems to keep most of my signal at about
> 50-70% of the total available power.
> What percent of the signal can i drive past this point?
> I know driving the peaks over this level will result in the signal being
> clipped or distorted, but to what extent? Is there any amount I can push
the
> peaks over or is this a line I should never cross?
>
> I suppose this is where compression comes in handy, bringing down the
peaks
> and raising the lower levels, but I have no such equipment to work with at
> the moment.  I can also see how my inconsistant mic handling is also
comming
> into play.  Will I just need to ride the audio level by hand until I get
> more consistant with my mic?
>
> I have a single trace scope I am using to monitor the signal. Totally
> overdriving the audio level produces obvious flattopping, but it is very
> difficult for me to pick out when this clipping first starts to occur
while
> monitoring voice signals.
>
> I think this is where a two-tone test would come in handy, unfortunately
the
> only af generator I have available is my touch tone phone held up to the
> mic!  I can definately see the point at which the clipping starts to
occur,
> but this seems somewhat useless as changing the input level of the audio
> signal (moving the phone away from the mic or turning my head while
speaking
> or holding the mic some inches closer or away) will change the audio level
> setting where clipping will occur.
>
> Any advice would be appreciated.
>
> tnx
> kb9tqo/ag!
> -ian
>
> _______________________________________________
> List Administrator: Duane Fischer, W8DBF **for assistance**
> dfischer at usol.com
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