|[AMRadio] FS: restored Gonset G-76|
brett.gazdzinski at verizonbusiness.com
Thu Feb 9 08:22:07 EST 2006
I dug out the G76 last night, and gave it a workout.
I need to take care of the audio, the receive is not that bad
with the IC chip I have in there, but to much hiss.
I had it on 40 meters, and with the dummy load selected, I was
picking up sw broadcast stations at s9, the thing is sensitive,
likely more sensitive on the lower bands than it needs to be...
The TX audio sounds like crap with the D104, it had problems
making much over 50% positive, with plenty of distortion.
I tried some other 6DQ6 modulator tubes with no improvement.
Phasing made no difference, but reducing the RF power made
things better, up to 90% at about 40 watts out.
Plenty of grid drive, 685 volts on the high voltage...
Its restricted, ok for a small signal, but the waveform
on the scope looks all screwed up.
So I am thinking about gutting the audio, and putting
in something like a pair of 6CA7's in AB1, driven by
a phase splitter circuit.
I do not like the postage stamp size driver/audio output
transformer, what with the 6DQ6's needing driving power.
It should be a fun project to get the thing working a little
bit better then it does now.
> Dan says:
> I have not seen any mods on the Internet for G76'ez...
> Anyone know of any?
> Reply from Jim WD5JKO:
> No not too much that I've seen. I have two G-76's
> myself, and the quality of the power supply is a
> factor in the quality of the transmitted signal. I
> have a home made (not by me) AC power supply that
> weighs a ton, and has a 3 tube regulated low B+. I am
> sure this helps.
> As Bret mentioned, the rcv audio output tube is also
> the audio driver for the xmit 6DQ6's. Having good
> fresh tubes here goes a long way towards better
> quality. Since the output tubes are acting as hi-mu
> triodes, the idle current could be too low if the high
> B+ is also too low. I forget how I did it, but I have
> a plug in meter that measures modulator cathode
> current. I also fiddled with that audio output stage
> by beefing up the idle current on xmit (maybe I did
> that on my G-50..), and heavily AC bypassed the
> cathode resistor, and added a little bit of inverse
> voltage feedback. Both receiver, and transmit quality
> stock seemed pretty decent, and was much better after
> the above said modifications.
> For receive, some say the IF band with is kind of
> broad. I recall cutting out some resistors that were
> across the IF coils. Without the resistors, the "Q"
> was higher, and therefore the bandwidth was more
> Six meters is a joke on the G-76. Don't try it unless
> you want to burn up your 6DQ5.
> If you are interested, I might be able to open up one
> of my G-76's so that I can document whatever I did.
> --- dw73454 at alltel.net wrote:
> > THIS TIME TO THE LIST ON PURPOSE...heheheheh...
> > Brett sez:
> > > The receive audio sucks.
> > > And the TX audio sucks (surprise!).
> > Hmmmmmm....I have heard G76s on 10 meter AM that
> > sound great! I wonder what they did to improve the
> > TX audio?
> > I have not seen any mods on the internet for
> > G76'ez...
> > Anyone know of any?
> > Dan
> > AMRadio mailing list
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