[AMRadio] FS: restored Gonset G-76


Jim candela jcandela at prodigy.net
Sat Feb 11 12:53:44 EST 2006


Brett,


   You are correct about the rolled off low frequency response on a G-76.
That said, these rigs "stock" seem to have more lows than say a Heath
Apache. One caution however is that the stock iron cannot take a lot off
bass, so any bass to midrange boosting attempt needs to take that into
consideration. Since a "flat" transmitter response of say 80 hz to 4000 hz
will sound bassy and muffled in the average receiver with a 5-6 Kc IF
bandwidth (@ - 6db),   you might add consider adding additional low end to
that G-76, but do so at somewhere between 3-10 db down from the 1 Khz level.
At 6 db down, the iron only has to handle 1/4th the power, so low frequency
core saturation is likely eliminated, and you can still broadcast down to 80
hz. Maybe bridge that 470 pf with a series R-C instead of just making a
bigger C, and you could manipulate the hi-freq roll off with some R & C
additions instead of just that .001 to ground.

    It would be interesting to take that G-76, and add a voltage divider to
the modulated B+ so that you can put the scope in X:Y mode to look at the
Trapezoid pattern. I use this mode all the time with my 20a + linear
combination, and the Trapezoid is VERY useful towards setting up the linear
for a minimum of distortion. With plate modulation, the Trapezoid is less
necessary, but still useful when setting up, or evaluating a transmitter. A
plate modulated class C amplifier usually modulates upward better with
increasing drive....to a point.

Jim

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Brett gazdzinski
Sent: Thursday, February 09, 2006 9:22 PM
To: 'Discussion of AM Radio'
Subject: RE: [AMRadio] FS: restored Gonset G-76


I guess I have different expectations then most here.
I would say its not possible to have the G76 sound good
on receive or transmit, what with the design and parts
they used.
You have a 470pf (yes, that pico)coupling cap between the 1st and
second stage microphone amplifier, and they inject the
receive audio in there also, and that uses another 470pf (yes pico)
coupling cap, with a .001 to ground.

How can anyone get nice lows with a 470pf coupling cap, or highs
with a .001 to ground. I would think a good telephone would have
a better frequency response.

We wont even get into the modulator grid driver/audio output
transformer, which makes the dx100 driver transformer look massive.
As an audio output transformer, it looks like it would be good for
about 1/4 watt output.

The mike input amp has a 470K resistor to ground, no way you
are getting any lows at all there....needs to be like 5 meg
for lows with a D104.

I did some playing around with it tonight, and found two problems,
a bad 12ax7 mike amp, and also found the modulation gets better with
much more grid drive.

I have some changes to do in the mike amp stage, but it sounds
back to its old self as long as the output power is below 60 watts.

The audio waveform looks ok up to 100% mod at 60 watts, any more
and it starts looking funky, I did not look into the driver tube
and its circuit yet, or the clamp tube screen circuit in the RF output.

Brett
N2DTS



>
> Hi Guys,
>
> I have been following this thread and I also agree with Charlie.
> My G76 gets great audio reports as it is. I am using a D-104 and have
> very good audio reports. I am currently listening to a group on the
> East Coast using a a 5" Motorola Micor speaker and it sounds great.
> Power out is around 70 - 75 watts into a sloper. I use it to
> check into
> the Midwest Classic Radio net on Saturday morning on 3885, the DX-60
> net on Sunday morning on 3880, on Tuesday the Southeast AM
> Radio net on
> 3885, and the First Wednesday CCA AM net on 3880. Believe me if it
> sounded BAD I would get chastized on the CCA net since I am the
> coordinator of the event. (defense if needed) My 32V-3 is under going
> major surgery and some day when I am retired it will get finished. We
> encourage the use of anything on the CCA net that runs AM and I am
> living proof that we abide by that.
>
> Anyone out there using a G-76 mobile?  I have the mobile supply and
> would like to give it a try.
>
> 73 Larry WA9VRH
>
>
>
> On Thursday, February 9, 2006, at 06:44  PM, k0ng at inebraska.com wrote:
>
> >
> > Jim:  I agree with all of your comments as my G76 works well as is.
> >       Not that anything cant be improved but....if it aint broke ..
> >       Maybe in this case, there is a problem ??
> >
> > Regards to all,  Charlie,   K0NG .
> >
> >
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