O.K. I have just received a brand new Cobra 19DX IV and was wondering how you can turn down the power output. I will be using the radio to drive an amp and need no more than 2 watts to feed into it. I have searched the web up and down and found no info. other than schematics on C.B. Tricks. Is there a variable resister to turn etc? Thanks for the help.
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WATT's the problem
- Thread starter onefastneonrt
- Start date
I've not owned that particular radio so no first hand experience, the following info was found with a google search...
RadioMods and S&M Software Forum :: View topic - Cobra 19 DX IV mods???
RadioMods and S&M Software Forum :: View topic - Cobra 19 DX IV mods???
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BOOTY MONSTER
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I have seen that link but still scratching my head.
See I am using that radio because it's the only radio that will fit in my little Dodge Neon and I really don't need all the bells and whistles.
The amp is called a 100HL that's it. A buddy of mine named, Cheech on here, had made a post on it and found some info. According to Switch Kit - Made by Joe at J&S CB Radios in San Gabriel, Southern Cali, A.M. only amp, Finals are 2X453's, and usually does not like no more than 2 watts of drive. It sort of looks like a Texas Star 350 but with 3 toggle switches. I had a Uniden PC-76XL hooked to it for a while and at low power the amp did fine but on high it pinched up badly at 4 watts of drive. I lowered the power on the radio to 1.5 watts and that little amp did a lot better.
I did have that Cobra 19DX IV hooked to a bird meter and it dead keys 3.5 watts but swings to 8 watts on modulation. Yes this radio was brand new in the box from Big Lots. Weird huh. Way to much power for that little amp.
"I had a Uniden PC-76XL hooked to it for a while and at low power the amp did fine........"
leave the Cobra 19 alone and use it with the 100HL in the low power position.
leave the Cobra 19 alone and use it with the 100HL in the low power position.
I would have to agree with from my own past experience. I've still got a little 100wicker, and when set on low with a low-powered/stock Cobra 29LTD radio hooked up, it will swing all the way from 10w to 100w. Mine did great just like that. If you are going to change the deadkey power lower on the radio, it will help the overall swing distance. But I wouldn't want it have any higher modulation by turning it up. The more you push on the radios output/final by always overdriving it; the quicker it will fail. Use a D104/M5, your radio with the deadkey turned down a tad, and run the 100w'er on low, have a coke, and a smile. That, and a K40 or a Wilson 1000 should make it all that it can be. Runnung any amp on the low side always sounds better; I haven't ever seen it different than that. When I had mine on 100/hi; it compresses the modulation and it sounds 'poopy'. lol!
Well thank you every one for your help and insight. I did some reviewing on CB Tricks and I think I found my solution. On CB Tricks web site they have all schematics and service manual for the 19DX IV. Looking through the service manual I discovered on page 11 and page 15 #2 that in order to adjust output power you tune or turn LT1. I posted the PDF files so if you would like you can take a look and maybe verify that LT1 adjusts the output power.
The first PDF is the service manual and the second is the schematic.
The first PDF is the service manual and the second is the schematic.
"messing" with LT1 will get you nowhere. this inductor is adjusted for maximum output for a reason. any attempt by you or anyone else to use LT1 to reduce carrier output will also result in a dramatic decrease in modulated output power levels as well. re-read my previous post and follow the advice contained therein.
the low power position on the 100HL could also be labelled "hi-drive". that's because the resistor-divider input network is "padding" the drive input from the 19DX. what you are looking to accomplish has already been provided for you in the amplifier design. use it.
the low power position on the 100HL could also be labelled "hi-drive". that's because the resistor-divider input network is "padding" the drive input from the 19DX. what you are looking to accomplish has already been provided for you in the amplifier design. use it.
I see - On this particular amp I am beginning to think that hi/low switch is more like an am/ssb switch.
I no nothing of this amp and I am learning new stuff as I go and from every one on here.
I am not trying to argue with you freecell but I know for sure that on a 4-watt drive on the low setting the amp only produces 60 watts with marginal audio quality and got very pinched up on the high setting. Yeah I know 4 in and 60 out is great but I would like to utilize the high side if necessary. With 1.5 watts in, audio cleaned up a lot and the high side sounded beautiful with max output at 120 watts on the high side. On a non-skip transmission with a Uniden 76, 100HL amp, and Wilson 1000 I could talk 50+ miles. I will try the 19DX IV the way it is and see what happens. I appreciate the help freecell and to all the others and who knows maybe the darn thing will be fine the way it is.
I no nothing of this amp and I am learning new stuff as I go and from every one on here.
I am not trying to argue with you freecell but I know for sure that on a 4-watt drive on the low setting the amp only produces 60 watts with marginal audio quality and got very pinched up on the high setting. Yeah I know 4 in and 60 out is great but I would like to utilize the high side if necessary. With 1.5 watts in, audio cleaned up a lot and the high side sounded beautiful with max output at 120 watts on the high side. On a non-skip transmission with a Uniden 76, 100HL amp, and Wilson 1000 I could talk 50+ miles. I will try the 19DX IV the way it is and see what happens. I appreciate the help freecell and to all the others and who knows maybe the darn thing will be fine the way it is.
Doesn't your amp have a separate Hi/Low, On/Off, SSB/AM, and RecieveAmp on/off? Most of them do. When an amp is set on the 'low' setting; it runs an amp mode called PEP (or 'Peak Envelope Power) which is letting the amp let the modulation move it twards full 100w. This great swing from 10w-100w gives great depth and vocal clarity. IMO = this is the way to fly.
The 'High' side switch sets the amp function of 'RMS' (which stands for 'Root Means Square'). In this mode, the amp shows a high dead key watt output - like what you are describing above. 60-90w swing. Modulation of you voice will sound 'squished' but will have a strong output. But your voice will sound squished; not sensitive or dynamic or large and not as some would want. It is the ability of getting a radio to get the largest, widest dynamic change of swing watts that give it great audio character. That is why the 'low' side is as popula as it is. The time that most people use the 'high' side is when talking skip. That's what I do - anyway. Some amps even have high/med/low; but the same rules of modulation still applies. The 'mid' is exactly what it sounds like; neither widely dynamic nor highly compressed.
The 'High' side switch sets the amp function of 'RMS' (which stands for 'Root Means Square'). In this mode, the amp shows a high dead key watt output - like what you are describing above. 60-90w swing. Modulation of you voice will sound 'squished' but will have a strong output. But your voice will sound squished; not sensitive or dynamic or large and not as some would want. It is the ability of getting a radio to get the largest, widest dynamic change of swing watts that give it great audio character. That is why the 'low' side is as popula as it is. The time that most people use the 'high' side is when talking skip. That's what I do - anyway. Some amps even have high/med/low; but the same rules of modulation still applies. The 'mid' is exactly what it sounds like; neither widely dynamic nor highly compressed.
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the terms for these "modes" were erroniously used in hooker amplifiers and have no meaning other than they refer to two power levels that the amplifier is capable of, one providing input padding and the other with no input padding at all. some dummy thought it would be cool (and confusing) if they used pep for low power and rms for high power. it's all bullshit. an am transmitter or amplifier operating in am mode delivers a 100% modulated signal when the resulting output yields pep levels that are just at or under four times the carrier level. hooker amplifiers are class C and odds are good that your 100HL is also class C.
proper operation can only be achieved by shaping the carrier and pep output of the exciter (transmitter driving the amplifier) to represent a 4:1 peak-to-carrier ratio and that ratio is only maintained when in use with a class AB1 amplifier as one of the characteristics of class AB1 is that it does not alter the proportion of peak-to-carrier power fed into it. this "shaping" can only be done in the transmitter itself as one of the characteristics of class AB1 amplifiers is that they produce output in the same proportion to the drive input. for example, if the input is 4 watts carrier and 16 watts pep the amplifier will yield 40 watts carrier and 160 watts pep.
the only method for re-shaping the peak-to-carrier output in the Cobra 19DX is to construct an RC shaping circuit and substitute it for the negative peak clipping rectifier in the transformer output that feeds the collectors of the driver and final stages simultaneously. properly done, this will allow the lowering of the carrier output without diminishing the modulated peak envelope power levels. at this point it's a simple matter of properly adjusting the AMC control to maintain the required 4:1 peak output.
since the 453 is a 60W device and there are presumably two of them in the 100HL optimum results will be produced when the carrier output of the 100HL is approximately 30W and the modulated PEP value is just at or under 120W. furthermore, if the 100HL is class C (it is) the proportional relationship between the drive input levels mentioned above and the resulting output of the amplifier will neither be had or seen. this only serves to make proper matching of the 19DX to this amplifier even more difficult.
the easy solution would be to leave the 19DX as is and find a well built, well designed class AB1 amplifier that provides three power output levels and in the medium power setting the output of the amplifier will very closely mimmick the output levels of the 19DX with no modifications. the power output of a 19DX is the same as every other FCC certified transceiver, that being 4W carrier and anywhere from 12 - 18W pep. output from a class AB1 amplifier in the medium power setting (nominal input padding) excited by the 19DX would be roughly +/-40W carrier and +/-160W pep with a resulting modulation index of just at or under (1) or 100%.
your bird 43 will have to be outfitted with the peak reading adapter kit to be able to make the required measurements.
proper operation can only be achieved by shaping the carrier and pep output of the exciter (transmitter driving the amplifier) to represent a 4:1 peak-to-carrier ratio and that ratio is only maintained when in use with a class AB1 amplifier as one of the characteristics of class AB1 is that it does not alter the proportion of peak-to-carrier power fed into it. this "shaping" can only be done in the transmitter itself as one of the characteristics of class AB1 amplifiers is that they produce output in the same proportion to the drive input. for example, if the input is 4 watts carrier and 16 watts pep the amplifier will yield 40 watts carrier and 160 watts pep.
the only method for re-shaping the peak-to-carrier output in the Cobra 19DX is to construct an RC shaping circuit and substitute it for the negative peak clipping rectifier in the transformer output that feeds the collectors of the driver and final stages simultaneously. properly done, this will allow the lowering of the carrier output without diminishing the modulated peak envelope power levels. at this point it's a simple matter of properly adjusting the AMC control to maintain the required 4:1 peak output.
since the 453 is a 60W device and there are presumably two of them in the 100HL optimum results will be produced when the carrier output of the 100HL is approximately 30W and the modulated PEP value is just at or under 120W. furthermore, if the 100HL is class C (it is) the proportional relationship between the drive input levels mentioned above and the resulting output of the amplifier will neither be had or seen. this only serves to make proper matching of the 19DX to this amplifier even more difficult.
the easy solution would be to leave the 19DX as is and find a well built, well designed class AB1 amplifier that provides three power output levels and in the medium power setting the output of the amplifier will very closely mimmick the output levels of the 19DX with no modifications. the power output of a 19DX is the same as every other FCC certified transceiver, that being 4W carrier and anywhere from 12 - 18W pep. output from a class AB1 amplifier in the medium power setting (nominal input padding) excited by the 19DX would be roughly +/-40W carrier and +/-160W pep with a resulting modulation index of just at or under (1) or 100%.
your bird 43 will have to be outfitted with the peak reading adapter kit to be able to make the required measurements.
Well I just talked to him on his radio and with the amp on hes pinched up bad. Without the amp hes no longer pinched up.
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