The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

timrim

Well, the 470 ohm resistor is a starting value and may need to be increased, 470 is a common value used with the small signal transistors (yours is a power transistor). Giving it some bias will help keep the transistor operating more stable and reliably. The 15pf cap will not let quite as much RF ge...

timrim

A half watt resistor will be ok and the 15pf cap should be at least 50 volts. Most disc caps don't have the voltage rating on them, but you should not run into any problems if you find one in your junk radios. Radio shack sells a bunch of disc caps (Catalog #: 272-801), perhaps you will find a 15pf ...

timrim

Ok, before we consider rebuilding the RF keyer, there are 3 thing that I would like you to do. First replace the capacitor going to the keying circuit, its currenty a 47pf which is larger than most RF keyers, put a 15pf in its place. Then give the transistor some bias by adding a 470-1000 ohm resist...

timrim

The circuit you sent me is very crude at best and has no bias. When I get to work, I will draw a suggestion to try with the transistor you are using, but I will also send you a schematic of a more reliable RF keyig circuit that you probably should use to replace that one.

timrim

email sent

timrim

that TO220 transistor with the diodes attached to it is the RF keyer, can you get me a pic of it with a camera angle facing it, so that I can better see how its connected and also see the part number?

timrim

I never knew radio shack even made a peak reading watt meter, are you sure its supposed to be peak reading?

timrim

A pic may possibly help, it would be great if you could shine a light from behind the board so that I can see the traces too. Try to get a very close up of the keying circuit. The relay may or may not be near the RF keying circuit, so just to be safe, get at least 1 shot of the whole board.

timrim

I really liked the Cobra 200GTL, I sold lots of them. They are nice radios if you make sure you have all the tech bulletins up to date. Lot of bang per buck. A lot of shops gave the radio a bad name because they lacked the skill to work on them. The 200GTL uses extremely small surface mount parts, m...

timrim

Actually the audio IC is a UPC1156, and you are correct, they are no longer available. Junk radios are the only way to get a replacement.

timrim

It sounds like the RF keying circuit is either too sensitive or poorly designed. Can you supply me a schematic of the amp, or at least the keying circuit? One other possibility is that he may be using low grade coax between the radio and amp, the RF signal from the towers may be getting in through t...

timrim

I am repairing a Alinco duel band 2-meter/70cm radio. The UHF final is bad and it is a 2SD1761E

EDIT:Never mind, upon closer inspection I discovered that the unit needs an M57788M power module for output, I think I can locate one of those.

timrim

What is your peak power on AM?

timrim

The problem is, without proper equipment, you have little chance of aligning a radio. To completely align a radio, you need a wattmeter, signal generator, sinad meter, oscilloscope, frequency counter and a 50ohm non inductive dummy load at bare minimum. You can do a basic power output alignment with...

timrim

If you are talking about an external amp, and its not high drive, then with the amp out of line altogether, set the radios dead key between 2 and 3 watts for good results.

timrim

They are off at the lower end, in fact, they are off about -8dbm, if I remember correctly. Also, when I calibrated it with top of scale, my 500mhz marker, which is calibrated at -60dbm, would not agree with a 500mhz -60dbm signal injected at front of analyzer. Now, they are pretty close. You have me...

timrim

I am calibrating an Advantage Instruments ITC 1300C Spectrum Analyzer, I am calibrating the attenuator switch settings by injecting a known (Lab Standard) signal strength into the unit. My question is: Would it make more sense to inject the proper amplitude signal and calibrate the attenuators at ha...

timrim

Thank you, Rick!

I think it is just the word code, so it looks like we will be ok. I just googled this radio, looks very nice, don't know why I never saw one before. The win-george software looks nice, I think he is going to have me make the computer interface.

timrim

What is the possible causes of the word CODE flashing when this radio is powered up. The radio is not yet in my care, I am trying to help the gentleman determine if it needs to be sent to me for service. I have been repairing Radios since 1975 and have yet to even see a President George, so it must ...

timrim

Go Tektronix. I just bought several more recently. They are the most reliable and accurate scopes made. Just check out Tektronix history. If you can afford a scope with cursers, you will love it for fine measurements. Experts recommend going 3-4 times over the bandwidth of the highest frequency you ...

timrim

If you are just adjusting the waveform for max on the scope, then you could substitute an rf voltmeter. If you don't have one, then you will need a sensitive analog VOM, and, you will have to make an rf probe. You should be able to Google it.

timrim

Yes, your radio will need to be on a 50 ohm dummy load, just clip the probe on the wire that goes from the circuit board to the SO239 jack. Remember to start on a high volts/div setting on the scope and work your way downward. A lot of the radios will read over 100 volts peak to peak or higher on th...

timrim

I always simply use a X10 probe connected to the antenna jack for rf output measurements. Just make sure your probe is good to at least 40 mhz and you should be ok.

timrim

Awesome thanks!

timrim

I would like to program a few eproms and try them in various radios. Does anyone have the eprom program data and hookup instructions for any radios?

timrim

Glad you got it working, apparently I read your original post too quickly and somehow got the idea that it was a tube amp....sorry!

timrim

The nice thing about the UTB by magnum is they are totally independant and sound really nice, well worth installing, I go through lots of them.

timrim

Just a quick idea, did u remove the metering jumper and see if the excessive current draw is gone?

timrim

Do you have an oscilloscope or a signal tracer? If so, I would look through the audio sections, and the transmit chain to see where the signal originates.

timrim

Yes, I have successfully set up many radios with MOSFETS and they do a very nice job of driving an amplifier.

timrim

Yes, I have the data somewhere at work and I will have to peek at it.

timrim

Normally all you would need to do is re-tap the tank circuit coil for 11 meters, the higher in frequency you go, the shorter the coil will need to be, this does take some experimentation. If you know the values of the plate and load caps, you could calculate the inductance needed and just tune the c...

timrim

Yes, it's the dead key that is really important to an amp, the modulation does not matter alot because the voice peaks are momentary instead of constant. A swing kit is better because if you de-tune the coils, the modulation will normally drop right along with it, resulting in lower output from the ...

timrim

Unless it says high drive 4 watts max dead key, setting the dead key at 2 or 3 will give better modulation, and the amp will run a bit cooler.

timrim

speedracer6g wrote:its a 142gtl radio. the mixer crystal is 10.24mhz and the pll is a mb8719.

thanks

MIKE

That is the reference oscillator crystal, you don't want to change it, you will find another crystal, either an 11.3258 or an 11.1125, Depending on if pin 10 of the PLL is tied high or low.

timrim

What model radios use the B-Kit? I don't normally stock the B-Kit but I can possibly calculate the crystal frequencies for you. What PLL chip is in the radio and if possible, what is the current mixer crystal in the radio?

timrim

Sounds like the squelch amp may be bad, I will take a look at the circuit when I get to work.

timrim

There are 3 leaders in the oscilloscope / test equipment industry, Tektronics, LeCroy and Agilent. I have not yet fount an Agilent scope that has similar features, price and warranty. Tektronics has been making oscilloscopes for over 70 years, so that is a plus, also their limited lifetime warranty ...

timrim

I am planning to purchase one of the following oscilloscopes in the near future, my current analog scope has served me well for over 10 years, but with current scope technology, I have decided to buy a DSO. Which of the following 2 scopes would you buy, and why? LeCroy WaveJet 324 http://www.lecroy....

timrim

Here is a link to the Pride 150, if memory serves me correctly the only difference is the output transistors.

http://www.cbtricks.com/Amp/pride/p_150/index.htm

timrim

I also owe Rick a very warm thank you for his help on troubleshooting a PLL problem on a Galaxy Radio, and his help in various other incidents. What people need to realize that the technicians time is valuable and that they could be doing things that make them money, but out of the kindness of their...

timrim

The PM feature don't work on this site, just email me at:

Removed

I will remove the email address from here later.

timrim

Where did you locate them? I did a google search but nothing came up.
I wish cbtricks would list sources for the products they show, I have been looking for BlackAdder products forever without any luck.

timrim

I finally located my long lost service manual for the Uniden export model radios. The Mixer output at test point 3 should be 2.8v PP but I am only getting 1.2 volts PP. The voltages on TR12 mixer is supposed to be: E.- .4 B.- .33 C.- 7.07 But I am getting the following voltages on TR12: E.- .4 B.- ....

timrim

Ummm, which of the above radios ARE export radios and NOT standard CB's? Answer: None of them! They are all standard CB Radios! :lol: Please think before you stick your foot in your mouth. I stand by every word that I said! Please don't bother to reply, I will no longer feed the trolls here. Getting...

timrim

MosFets are NOT designed for use in standard CB radios Yes, they are! The design engineers at Ranger and Galaxy are both using them, and I am not talking just the 10 meter radios either, The Galaxy DX929 DX939 DX949 DX959 DX979 use them. Texas Ranger uses them in all their CB models. I don't have t...

timrim

It has absolutely nothing to do with what brand or model meter you are using, or even if you calibrate your meters every day on a lab standard. Proper installation of a MOSFET will increase your power output. Bottom line is this: If you install a MOSFET and do not see a big improvement in wattage ou...

timrim

I got my first one in about 1977 or 1978.

I will looks for a diagram and post it if I can locate it.

timrim

I would suspect that the VCO may need a slight touch up. It is probably best to simply align the whole PLL while you are at it. I remember doing some exotic mods to the 858, 861 etc. many years ago, and actually hearing notes being played as the channel selector was rotated, each click of the switch...

timrim

If it's done properly it does indeed work! I have done hundreds of them in Cobra radios, every model 25 and 29 from the XLR version to present time.

The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

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Alinco DR-570 UHF final needed

Calibration of Spectrum Analyzer

President George: Flashes CODE

Eprom mods

Which of the following 2 scopes would you buy?