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Therealporkchop
Junior Member
Username: Therealporkchop
Post Number: 34
Registered: 11-2002
| | Posted on Saturday, June 05, 2004 - 9:35 pm: | 
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Ok people, here's the deal...
I have a Galaxy 77 set up like this:
The 1N914 (1N4148) diode, no resistor installed in the R238 slot(if I remember correct). The 2SB754 transistor is changed to the 2SB817. The resistor for the limiter is history. It has the resistor mod (from Galaxy's site) for talkback installed also. The pots for the driver and final bias' are cranked wide open(or wide shut, don't know really). Keys are 4w,6w,11w. I show around a 45w swing PEP.
My questions are this: I know the watt rating on the 2SB817 is greater than the 2SB754, but what exactly does changing this do for the radio? I know it helps with dimming lights etc, but what does it do as far as power goes? I was told by one guy in a local repair shop that running my bias so high will burn up my finals, but I don't believe him. I've been running it this way for almost 2 years. I've been told the radio is loud and proud, but I don't know for sure. I am thinking of putting in a speech processor and I was wondering how I should set up this radio if I do. I was also thinking of changing my driver from the 2SC2166 to the 2SC1969. And maybe changing my two finals from 2SC2312 to MRF477 or MRF497. Has anyone ever done this or know anything about it? What about how I'm running my bias? Anyone know any other mods for this radio as far as loudness and clarity go? How about power output?
I know there are more things to do to this radio than what I've done, but it's real hard to get anyone, especially a repairman or tech locally to tell you anything. I guess everyone is scared that you'll have something louder than they do. Or maybe it's a matter of the all mightly dollar. Also, I'm wondering are there any mods for receiver improvement? I know I could get a pre-amp, but that defeats the purpose of homebrewing and the whole concept of D.I.Y, experimenting and the hobby of CB in general.
Last, anyone know of any mod where you jump power to the collectors of your driver or finals? A well respected repairman locally was speaking of this to someone I know, but I didn't really get the facts on it. Maybe he's just old and crazy, I don't know.
Thanks guys!! |
Tech548
Moderator
Username: Tech548
Post Number: 100
Registered: 5-2004
| | Posted on Sunday, June 06, 2004 - 4:18 pm: |
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Therealporkchop
The 2SB817 is a far better voltage regulator than the original. The original would work just fine if your radio was still in its stock form.
And having the bias on the finals set to high will do just as your Tech said. Sooner or later your finals WILL over heat and die. But, as you said, you have no clue where the bias is set now. Having the bias set to specs will let your radio run cooler.
Changing the driver to a 1969 will only result in a decrease in power output since there isn't enough gain in the buffer to drive it correctly. Otherwise, people would have been doing that long ago. And not only that, there is only a 1/2 watt difference between a 1969 and a 2312. Absolutely no difference on the receiving end between the two transistors.
A pair of 2SC2312 transistors will not generate 45 watts of output power. Somewhere between 36-40 would be more the norm. The only time you will see a true power reading is into a perfectly matched (52 ohm) dummyload with a 1.1 or less SWR. What you read into an antenna is a whole different ballgame as what you see from a good dummyload.
If you feel that you need more horsepower, install a 350 watt amp. You would be further ahead by doing that than working your radio so hard. And if you decide to go that route, your radio output would have to be turned down since linears don't have a longlife expectancy with 35-40 watts pounded into them.
About the only thing I would do with your radio at this time is have the bias checked on your finals. Other than that, it appears that you have a real smoke blower there.
I'm sure you'll be getting some other opinions posted here. Stay tuned.
Jeff. |
Therealporkchop
Junior Member
Username: Therealporkchop
Post Number: 38
Registered: 11-2002
| | Posted on Monday, June 07, 2004 - 3:01 pm: |
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What about updating my transistors to the MRF ones? Does anyone know of any other power mods for the Galaxy radios other than the diode in the R238 or R236 slot? |
Tech548
Moderator
Username: Tech548
Post Number: 108
Registered: 5-2004
| | Posted on Wednesday, June 09, 2004 - 4:38 am: |
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Therealporkchop
Pinout is all together different. We're not talking about a quick final swap here. In my way of thinking, you're expecting wonders from this radio. By the time the RF circuit is changed and a completely different set of finales are installed, the results wouldn't be all that impressive when you consider the money involved.
Why don't you just order yourself a high powered (100 + watt) radio? You will never get your Galaxy 77 to do the wonders that you are trying to get out of it. There is only so much that can be done with them. If you feel that you have outgrown this radio, then it's time to step up to a BIG radio.
Jeff. |
Lasthighlander
Junior Member
Username: Lasthighlander
Post Number: 14
Registered: 8-2004
| | Posted on Saturday, September 04, 2004 - 10:06 am: |
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I have a galaxy 44 that sounds like pretty much the same as your 77 porkchop. They took out the mirror board and installed jumpers, then removed the bias pots and put in big green resistors, they may be some sort of diode I`m not sure. Not a trained electical tech here,,lol. If your radio has the mirror board missing you can unsolder the jumpers, leave the one end going into TP8-9 soldered and check your driver bias between those 2 points. Then you will have to put in a jumper in TP7 to check final bias.I am going to check mine and try to get it back to as close to 100Ma for the final and 50Ma for the driver as possible, those are a little higher than factory specs but have worked well for me. |
Tech548
Moderator
Username: Tech548
Post Number: 279
Registered: 5-2004
| | Posted on Saturday, September 04, 2004 - 3:51 pm: |
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Lasthighlander
I don't have a problem with volting the final. That's why the mirror board isn't there anymore and that's OK.
What I never could understand is why anyone would replace variable resistors with 'fixed' resistors for biasing the driver and finals. Doing this does not compute with me. Can someone please explain!! Am I missing something by not replacing bias variables with fixed?
Jeff
Tech548 |
Lasthighlander
Junior Member
Username: Lasthighlander
Post Number: 19
Registered: 8-2004
| | Posted on Monday, September 06, 2004 - 9:05 am: |
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I am the same as you Jeff, I have had 4 radios that were gutted the same as this 44 I just got.Didn`t mean to sound like I was saying this was a good thing in my last post, was just telling porkchop how I tried to test my bias to see where the fixed component had it set at.I am going to check around some of the local shops and see if I can get the variable pots for my radio so I can try and get the bias back down.I am far from being an expert on electronics but I do know that I hate it when people take perfectly good radios and try to hot rod them as they did this 44.Alot of techs don`t like volting the finals but I have done this with many radios and none have gone down in smoke as yet. But ones I have seen where they hot rod them like this and remove all means of adjustment then do the volting, they usually don`t last long. |
Therealporkchop
Member
Username: Therealporkchop
Post Number: 56
Registered: 11-2002
| | Posted on Sunday, October 03, 2004 - 7:35 pm: |
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Well, I'd like a detailed run-down about volting my finals, if someone would please email me and start a conversation with me about it. I am learning here as well as trying to post my experiences and (little) knowledge. Also, this is a hobby to alot of guys, so changing the finals as I ask earlier is simply for the hobby of it. It isn't a matter of out-growing the radio or anything of that sort. It's a matter of just wanting to do it to say I did. I spend hours in my shack trying out stupid stuff. It's just to be able to say I did it. That's all. But please someone send me a email and help me with this voltage thing.... |
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