Galaxy Saturn Dead Key

[R00st3r]

I am trying to find out how to drop the dead key in a Galaxy Saturn but I want to keep the top end swing. Any help would be great

[Kelley]

Not sure on the Galaxy since I do not have a schematic. In the past I have found that by adding additional resistance in series on the plus voltage line that comes from the audio transformer on a switch you can drop the output yet keep most of the swing.  To achieve the max swing you still have to retune the adjustable chokes.  I think you will find that the low key is the way to tune and then let the high key stay at what ever it ends up.  Normally it is still as good as it was or close.  I am talking RMS now not peak readings.

I find it impossible to believe a wide-open peak meter on audio swing when the current draw is reducing not increasing.  Makes little sense except to make the operator feel good.  At least on AM.

Now as I have stated I have been out of this for a long time so the newer radios maybe different but find the circuit that feeds the B+ to the final and driver and should be associated to the audio transformer and a diode normally is an isolation diode sometimes they use SR1K-1.  This will come out of one sections of the audio transformer while the other section of the transformer will be the output for the speaker, external speaker, and PA speaker.  Make sure you have the correct pins for the output side of the transformer.  If you find that diode, on the cathode side separate the trace to the finals and wire in the appropriate level of resistance to change the bias.  Since I do not have a schematic it is hard to suggest any value other than start small say 50 ohms.  It does not take much to drop the carrier.  This will take some manipulation of adding resistance and retuning to achieve the results you want.

You can if you can find a small 20-turn resistor say 500 ohm or 1k add that across the cathode of the diode and the broken trace to the final and driver and adjust it instead of trial and error.  Or you can find a pot that you can use. 

Now once you are happy with the reduced carrier then you can wire a switch to the radio or outside the radio that will give you more or less a low drive and high drive with a lot more driving swing on the low side.  If your audio is lagging based on supply regulation then at this point you can add a capacitor tank that will assist the high loads to a point.  The capacitor should be no more than 220 Uf and since I am not clear on the working voltage for your radio at least double what the working voltage is.  Now the positive side goes to the cathode of that diode and negative side towards the finals and drivers with your new bias resistor or resistors.  Remember you can combine resistors to get the desired carrier.  Series will double while parallel will reduce by half the sum using any values.

I would only use the capacitor if it is needed.  If you get the swing you want then of course just forget it.

I would only use an RMS meter for adjustments to make sure your audio is clear and not distorted.

         

[nomadradio]

I have one question:

Are you willing to re-install TR32?

I'll guess that it has already been pulled out.

Mostly I stay completely out of the "super mod" discussions. Sure, you can make the radio louder than stock. You can reduce the carrier without making the AM audio TOO nasty, and still get the same PEP that 8 Watts of carrier would get you.

But since most folks who do this stuff are strictly "wattmeter worshippers", they end up with a transmitter that makes the meter happy, and only aggravates everyone who hears it on the air. Audio that sounds like it was processed with sandpaper, or makes the operator sound like he stuffed sweatsocks into his mouth before speaking.

Odds are you have heard the "super-swing" audio that I'm talking about.

Pulling TR32 is the easy, sleazy way to goose the wattmeter on AM. But it also disables ALL the limiting. Mostly, it disables the circuit that holds the mike amp chip below the point of distortion.

Now, I'm not talking about distortion from overmodulation. That takes place downstream from the mike-amp chip. Your mike audio splits off three ways from pin 1 of IC3, the mike-amplifier chip. It feeds to the FM modulator, the SSB modulator, and also to the AM modulator circuit. Feed distorted audio INTO these, and there is NO way to clean it up downstream from this point in the circuit. TR32 serves to hold the audio level on pin 1 of IC3 below the distortion point BEFORE it feeds into the radio's three separate modulator circuits.

Pulling TR32 also disables the limiter on SSB transmit. If you don't care about sideband transmit audio quality, that's your decision But there is another drawback to pulling TR32. If you run the radio on SSB transmit, you will poof your driver, finals, and the AM modulator transistor. Not necessarily in that order, but unless the SSB limiter (ALC) is working, the average power on SSB goes through the roof. Sorta like turning the AM carrier to 20 or 25 Watts. Turns the metal tabs on the driver and finals black from the heat, if you do this for long. The heat load will pop them before long if you keep it up. But the bonus is that overdriving the RF power stages on SSB will also sound really, really, really NASTY! Overdriving the AM modulator can be done, and you'll still be understandable There's a "middle ground" between "loud" and "what did you say?" for AM transmit. But on SSB, this just is NOT possible. Sideband is different. It's that simple. Without TR32, sideband will be nasty. Unless you play the mike gain knob like a violin. But NOBODY turns down their mike gain enough to sound clean on sideband, once TR32 gets disabled or removed. NOBODY.

So I'll make you a proposition:

If you'll agree to install a 2SC945 transistor at TR32, I'll tell you what to change to make the Saturn do what you want.

Mostly, I'd rather not have my name associated with radios that sound like a mouth full of sweatsocks playing a kazoo. Even second-hand or third-hand.

Turning the AMC control VR14 will get you all the AM modulation you can use, once TR32 is installed. But at least the audio signal that feeds INTO the AM modulator circuit will be clean, and any distortion will be taking place IN the AM modulator, and NOT in the mike-amplifier section.

Let us know if you're willing to install TR32 where it goes, and I'll describe what you need to do.

One more detail: I need to know WHICH Saturn you have. It was in production for 14 or 15 years, and was revised almost a dozen times from the oldest to the newest version. If you can find the circuit-board's ID number, that would make it easier to point out where things will be found. It will start with the letters "EPT", followed by the digits "3600", with two more digits between 10 and 14, and one letter after that. Newer versions have this number printed along the front edge of the pc board.

And if the ID number starts instead with the letters "SRT", found on the solder side near the TA7222 audio chip, your Saturn is REALLY old. Old enough to vote next week.

73

[Kelley]

Absolutely I agree with the previous gentlemen, if your audio is good now with the carrier out at present then there is nothing to do.  However, if you are looking for a low drive for an external low drive amp then what I have suggested will work as good as any.  Removing a transistor ALC is never a good idea but there are ways to make it less limiting especially if your modulation circuits are minimal at best and in some radios this is shortchanged.  Sometimes just clipping the resistor in the smoothing circuit will do the job and give you a little more audio.

I also agree that trying to bust the meter with audio swing is causing nothing but distortion.  I use to find it amusing folks would sound like crap and then tell me hey man I am keying 6.5 watts and swinging to 30 or 40 watts.  Yet when I retuned the radio back to 3.5 and good forward swing on a good wattmeter only a few watts rms then they sounded much better and got better compliments on their radio. I use to use a Drake W4 and if you got two watts of swing from any starting point your audio was clear but plenty loud enough to be heard.  Especially on cheap radios.  But even a cheap radio can be made to sound good if kept within the constraints of the radio design itself.

I had a guy bring his meter over once to show me what his radio was doing.  I put that on my personal radio, which I had changed to ECG 236 and ECG 235 and mine on his meter was keying right at 4 watts and swinging to over 45 watts.  I just looked at him and said do you really believe my little radio is putting out over 45 watts.  As I recall he had a peak reading meter of some off brand.  I then showed him on my power supply, which shows current draw and voltage stability and is a 35-amp 13.8-volt power supply.  His radio on my power supply clearly demonstrated his radio was actually backing up on current draw.  Current draw being reduced compared to increasing does not represent any forward carrier gain no matter what the darn peak meter shows.

Trying to get more and more carrier watts more likely than not is sometimes less beneficial in making the radio sound worse.  In addition the difference of 3.5 watts and 6 watts dead key is almost negligible on the other end where the intelligence is the audio…not the carrier.  It is much better to get to the 6.5 watts using modulation provided the radio modulation power is there to drive a 3.5 watts carrier.   That is what makes or breaks a good radio.

I know old school crap but I still think a modulation circuit in push pull of two 15-20 watt power transistors driving a decent audio transformer is a very good thing.  You can always cut it back if all the modulation is not needed using ALC or a pre amplifier with an adjustable speech limiter.  Much easier than trying to modulate a 4-watt carrier with a 5-watt audio driver not considering any losses that are going to be found.

Best to all,

Kelley




   

[R00st3r]

Thanks for the replys. I have not removed TR32 I have VR14 all the way open. I want the Saturn clean but to have good swing. Thanks for any help any one could give.

[The Rebel]

My Opinion!

People put too much emphasis on swing. Usually the swing you see on a peak reading meter is only splatter and a result of harmonics and parasitics being reflected back from the antenna.

A good 100% modulated carrier will out perform a low carrier high swing radio. I think people started the swing from looking at the meter during SSB operation and thought it looked cool. SSB uses a different concept of operation from AM, one being the type detector used.

If you use an oscilloscope to adjust the modulation will do better than a peak reading meter, but most CB'ers will not hear to it. I suggest all readers get books on radio principles and study them to help understand what is happening in a radio. Also my suggestion is, if you don't know what you are doing with a radio, stay out of it. Many of us on the forum have tried to help solve problems and people tend to listen to people who advocate the swing principle rather than the good sounding less splatter setup. Many failures I see in repair service are inflicted by untrained technicians modifying a perfectly good radio to get more swing or put in a noise toy.

I will help anyone I can, but please, don't screw up a good radio thinking a lot of swing is going to benefit you. As stated in a post above, if you see a decline in current draw from the power supply, but more swing, your average power is actually less than the unmodulated carrier. The current should remain steady as you talk.

Removing parts the manufacturer put in a radio is not good. If you are an engineer, then you may redesign the circuit for better performance, but if this is the case, why not build your own radio.

Please help clean up the airwaves and properly set up your station and you will see better performance from your setup.

From the desk of the Rebel,
Registered Red Neck

[WILDRAT]

I'd just get rid of the radio and buy another one. There is a fella called WildRat here on the forum that will take all your old radios that work and in return send ya a bottle of Florida sand. You can throw it under your chair and tell them your in the Sand Pile. Oh, that WildRat will even let you pay shipping and handling on the old, classic, working radios.

[nomadradio]

Okay Rooster, here's the deal.

Your parts list:

1) 1N4148 diode
1) 1 Megohm 1/4 Watt resistor
1) 1K ohm 1/4 Watt resistor
1) 10 uf 50 Volt electrolytic capacitor.

Pull out C190. It's a 100 uf radial electrolytic cap. Replace it with the 10 Uf cap. Be careful to observe the polarity.

Find R238. It's a 5.6k resistor that has one end connected to the max carrier-power trimpot VR13. IF R238 IS NOT a 5.6K part, you need one. A 4.7k will work fine, if that's easier to find. Unsolder and pull up the end of R238 that is towards the outside edge of the pc board, away from VR13.

Now insert the cathode end of the diode, the one with the band on it, into the hole where one end of R238 just came out of. Solder this lead of the diode to the foil pad underneath. Don't clip the lead short yet.

Lap the free end of the diode to the free end of R238. Solder them together, and clip the excess length from the diode lead ON THIS SIDE ONLY!

Now, on the solder side, clip the diode lead sticking out of the foil pad, but LEAVE ABOUT A QUARTER INCH of it sticking out.

Cut one end of the 1 Meg resistor to about a quarter inch in length. Lap-solder this end to the quarter-inch long stub of the diode lead, still sticking out of the foil pad. Lay the 1 Meg resistor down against the adjacent ground foil, and solder the free end of the 1 Meg resistor to ground. You can clip this end of the resistor short, or curl some of it up as a handy place to attach the ground clip of a 'scope probe, should you need to poke around in it at some later time.

Remove R253, which is a 15k 1/4 Watt resistor about halfway between the mike preamp chip IC3 and the speaker-amp chip. Install the 1k resistor in place of R253.

You will usually need at least 2 Watts or carrier to keep from sounding nasty, even with this setup. But you'll get the same peak power output that you did with a higher carrier power.

And if you choose to experiment, and try "just one" part of this, or whatever, that's your business.

And if they keep saying "WHAT?" when you transmit, this would be a clue that your 'experimental' setup is not exactly quite right.

73

[R00st3r]

I did just as you said and it worked just as I wanted it too. Every one said it sounds great Thank you so much.

[nomadradio]

Way cool!

Congratulations!  Glad to hear it turned out the way you wanted it.

73

[SinCity 181]

Way cool!

Congratulations!  Glad to hear it turned out the way you wanted it.

73

nomad  I have a turbo also with the ept295013z pcb, and I noticed that r238 is no where near vr13. I know these have been changed over the years. Do you have the info to do this mod with this pcb #? Thank you.

[nomadradio]

Even though the mike audio and AM modulator circuits are mostly the same for these two radios, the schematics and callout numbers are NOT. The parts list above is the same.

Both the callout numbers and physical locations are different. I'll dig out a 2950 schemo and update the post above to match  your main pc board.

Later.

Time to turn off lights and head home for tonight.

73

[SinCity 181]

Thank you sir.