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  #9  
Old 11-02-2009, 06:09 PM
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Quote:
Originally Posted by unit_399 View Post
There are lots of ways of reducing the output of a CB: Detune the final tank circuit; Reduce the predriver output to the driver and final; ect.. Probably the easiest way is to use a fixed resistance to reduce the collector voltage to the driver and final. You can use a rotary switch to switch in various resistors to get diffferent power levels. Easy and Cheap.

- 399
Now there is an idea!
See, that is why a thread such as this needs others to join in.

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Old 11-03-2009, 09:04 AM
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This is just meant to go over the basics of building a lab power supply out of an old atx power supply. The first thing i will do is go over the basic pinouts & wire colours you will need to worry about.

Green - Power On to power supply
Gray - Power OK (for your status light)
Black - Common (ground)
Purple - +5v DC Standby (not used)
Orange - +3v DC
Red - +5v DC
White - -5v DC (removed in the 2004 atx power spec)
Yellow - +12v DC
Blue - -12v DC

Please note, that the -5v may not be there. It was eliminated in newer atx power supplies. Also that the negative voltages do not have a high amperage (they are limited to approx 5 amps or less). A full guide to the 20 pin molex connector pinouts can be found here: ATX power supply connector pinout and wiring @ pinouts.ru

The first thing that needs to be done before you start hacking into the unit is to test it. I prefer to use an old hard disk. plug it into one of the molex connectors, and jumper the green wire to a black wire. This should give you a base load and allow it to start up so you can verify your voltages.

Once you have the supply tested, you can go about to hacking up the wiring. the first thing to look out for a smaller orange and red wires, these are for a signal reference, and must be connected somewhere to their respective wires, or the power supply will not operate, or could fry the voltage regulator.

So, as for building your case, and installing your binding posts, that is up to user preference, but i recommend attaching all the corresponding colored wires to their respective binding posts. it allows for a larger draw through the binding posts. How i did mine, was i twisted the green power on wire to a black common wire, and put a led & resistor inline to the black wire from the gray wire. Now depending on how lazy you want to be, you can either use a old hard disk for your base load, or use a 10w 10amp resistor across the 5v bus (between red & common). Without a load on the 5v bus, most of these power supplies will not give full voltage. Also make sure you have the smaller signal reference wires attached to your binding posts so that the power supply will regulate the voltage correctly, and that should be it

I hope this helps somewhat

-Jeff

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  #11  
Old 11-03-2009, 05:54 PM
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Thanks Jeff for the contribution to the thread, and welcome to the forums.

This is the type of responce I am looking for here. And for your first post, that was a great idea.
When you are on a budget this type of supply comes in real handy. Old pc's can be picked up at yard sales for less than 10 bucks. And you can also use some of the low voltage outputs. Make them varible and then you have a source to inject missing voltage on a radio for testing puposes.

Thanks Jeff.

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Old 11-03-2009, 06:27 PM
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anytime. The power supplys are capable of producing voltages of 3.3 to 24vdc, just through normal pinouts, and i have seen some information on re-wiring them into a variable voltage power supply. They are handy little devices.

Something else i would like to add, is for those of us who do wiring diagrams, a good PC based program (that is free), is called TinyCAD, available freely from sourceforge (big freeware repository) at TinyCAD - The open-source schematic capture program for Windows

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  #13  
Old 11-11-2009, 11:16 PM
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Default FREE SPICE and Schematic software.

Here is the link to some other Schematic and design simulation software that has a really good Yahoo support group with Lots of additional parts libraries. The Yahoo support group has links to instructional videos as well.

Linear Technology - Design Simulation and Device Models

LTspice : LTspice/SwitcherCAD III

Linear Technology primarily makes chips for Cell phone power supplies and switching power supplies but also has complete transceivers on a chip in the cell bands. Amazing technology but not really applicable to CB.

I have some old dead Uniden 510's I might have to resurrect. It would be neat if we could get a schematic of the old Sencor CB test sets and try to duplicate them. Over on CB tricks there was a suggestion by Mr.Ward that starting with a dead Galaxy 99 or any SSB radio with a freq counter would be a starting point. Not quite enough resolution on the counter though. Older lower than 100 MHz HP counters go for less than $100 on eBay pretty often. 7 digit resolution there.

I was thinking of just getting the 510's to output a carrier at a low enough level to feed into a SA602 or 612 which is a common active mixer in SSB radios. Would have to unbalance it to reinsert the carrier. I will use the schematic of my 2510 as a starting point since it has an adjustable carrier level. I guess any low level modulation circuit would be a good start. Maybe even a diode ring mixer since the loss through one is usually around 6db and would help attenuate the signal. Look at some of the older Ten Tec schematics from the Omni A or Titan radios from the late 70's and early 80's for reproducible circuits. Schematics are in the manuals. They made amps as well.

Ten-Tec: Downloads

Here is a really good read as well, all 100% homebrew, and very clear and easy to understand.

CRYSTAL SETS TO SIDEBAND

A Guide to Building an Amateur Radio Station
By Frank W. Harris, KIYE

download it here for free

Book Copyright (c) 2006, Frank W. Harris / HTML and PDF assembly Copyright (c) 2006 AmSoft

I'll have to make do with my basic items till the day comes and I can get a
HP 8920 or 8924c. I did score a Tektronix 2230 scope for less than $80 a couple years ago. Still need a decent counter but until I get back full time it will have to wait. Either that or go back OTR, but then I won't have any time for learning radio. Making it driving a forklift at a LTL company now till they add drivers or some land I own sells and I go back to school. Ordered my transcripts to see where I stand in that regard.

I love this topic. Make it a Sticky if it isn't already.
Thanks,
Hypo

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  #14  
Old 11-25-2009, 03:40 PM
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Hi I am somewhat new to radio repair but I love it and was wondering if you had any tips on becoming succesful.

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  #15  
Old 11-25-2009, 04:47 PM
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Nat19; this is the list as previously mentioned in the first post. It is the list for tools most needed. Besides tools, one needs also to practice good soldering and de-soldering skills. Learning to repair will take patience and starting with the easier things to do. Such as wiring an aftermarket mic to any given radio, doing your own coax connectors, understanding basic circuits - like power supplies, etc. Unless one is an apprentice at a radio shop, going to school to learn would be another means to acquire the necessary skills and knowledge. I have only modest amounts of repair knowledge and have been successful in some repairs/modifications.
I haven't yet ruined anything; but there is a first time for that - too...


Standard Shop Equipment
Here is some of the tools you will need to start repairing radios.
A good set of hand tools.
Regulated power supply.
Dummy load. (A home-brew 100 watt is fine)
Analog and digital volt meter.
25 to 45 watt soldering irons.
Solder wick
Solder sucker (Radio shack has a nice solder sucker iron. Get them while they last)
Assortment of test clips
Magnifying lamp (Well I need one)
Frequency counter
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BASE: Kenwood TS-2000, GAP Titan DX, Diamond X50A, Sirio SY27-4, and IMAX 2000.
MOBILE: Galaxy DX99V w/RF Limited CR-577 mic, Sirio Z-180. Yaesu FT-8800R & Diamond NR-770.

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  #16  
Old 11-25-2009, 05:01 PM
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Thanks one day I hope to be as good as you or maybe even better.

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