Cobra 142 GTL and 203/7505v amp??

[CB590]

I was looking at a classic 142GTL for a decent price. Has extra channels, unlocked clarifier, keys 4 swings to 9, does about 20 on sideband. Supposedly just tuned and aligned.

Never had a base rig ever and have been eyeballing these for awhile. I read VR6 can turn down the AM power so I can setup for an amp.

Anyone run a 142 with the mini KL-203 AMP? Wondering is the 203 or like the newer 7505v would be better?

Ask, what is the warmup time for a 142 to be on freq for sideband if it's a "good" one??

 

[Slowmover]

I have several KL-203 plus a 7505v.
My use has been mobile.
Uniden 880, 885, 890 plus Galaxy 99v2.

The latter pulls a whole lotta juice in comparison.
Is BIG. (Far more than twice the size).
And will do 140W easily where the former is 70W.

Between the two (for me) it’d come down to antenna efficiency (everything past the radio). I’m happy to have both given the low price of each.

Digital Signal Filtration ahead of the speaker means more to me in mobile use as a professional driver. That has no substitute.

.

 

[Handy Andy]

This may sound weird but to tie an amp to a Base radio - well that's fine but remember that the Power supplies used are going to have limits.

Since you're turning down the "wattage" of the Base to meet the amp - you may want to trim the Voltage output of the BASE's own Power supply - make sure it's not running anything more than 13.8Volts or if you can trim it down to 12.5 or so - even better.

Why that step? The power supply isn't really the problem, but the swings in loading on it is.

The Power supply for the Mobile amp, you'll need at least A 30-AMP. that's MINIMUM - I'd get a 50 Ampere and make that an adjustable type to get too.

Why these variables? Because of the loading and your effort to keep the harmonics' of one low enough not to wreak havoc in the other - on top of when you run lower wattage on one system, the overhead dynamics are affected too. The reduced carrier swings wonderfully on a meter - but it is detrimental in performance to a simple staged Class C or even the Class AB types of amps.

• - they have a general rule of don't exceed their input dynamic range. else they will clip or clamp - when you turn down the Radios' carrier - you improve it's swing factor.
• that is a Dynamic range issue - the swing is dynamic and not necessarily LINEAR - it's asymmetrical - not linear - rises and falls quickly - Audio in it does this, but your mixing Audio in with an RF signal - the RF signal power levels are the dynamics that change at the Audio rate - you may think it's slow enough - no it's not - you will clip if you swing too much power in PEP.
• You do not want the Mobiles power supply getting taxed all the time - the regulation inside the unit is not the issue,- it's the QUALITY of SENSE and how stiff the regulation is able to be, in keeping up with demands that are placed on it.
• Class of operation - Class C is fine for AM and FM - better if its' only FM or CW, but you don't have a lot of those willing to work your station that way these days. Class AB is better - but again you can cause clipping and potential damage if you don't keep the power levels that the Base radio can deliver - limited so the amps' ability to track and follow and amplify properly what the Base Radio is doing - remember the asymmetry part. The amp will have it's own asymmetry problems with dynamics the Base radio will put into it. - Class AB is worse-case application condition for swing or at least untamed for this - Class C - you have very little room for asymmetrical - it's already non-linear (asymmetrical) itself.
• When I refer to "untamed" there is little regulation of the Bias the amp will have in Class AB. This can affect the SSB signals and the ability of the Amp to take a quiet whisper onto a full bore bellowing call and operate it all within it's abilities and operational window.
  • As a Sidebar...
  • ​
  • There was a reason for this circuit in the older Uniden PC-122 models as well as some others in the earlier SSB days of this chassis - it was designed to sample some RF signal and PUSH it into the Bias of the next stage as a preparation - to RAISE it's drive current into the Base of the next stage - pushing it closer to CLASS A operation to keep the signal from becoming a non-linear.distorted mess. A lot of people think this is a swing kit, in a way, yes, but not like the kind you think it is. This helps to "tame" that untamed portion of the dynamics the AB-bias appears as to an SSB signal - a low whisper onto a "well that's nice" (a normal volume and consonant or constant conversation) the amp works just fine. The AB Class pushes RF linearly as it arrives Then; when you start getting more enthusiastic - the volume and inflections go up and come out in all their glory.- there's your distortion artifacts.- you simply run out of room. That is what the circuit does, gives the signal the ability to complete the cycle -even though little if any, more power is produced - the Bipolar just heats up but your not ruining your output.
  • This is a moot-point on MOSFET designs - because you don't have "Class A" - you have very little in any "knee" for linear - so it is more like a switch.
• The last thing you want is the Base radio overrunning your amp in power causing the clipping distortion because the RF-power output swings higher (not faster in Rate - only in POWER Drive) than the amp can follow it - you can see that and your round table friends may even hear this as a type of compressed audio - like a telephone can only produce so much volume before its' all crunched up.
  • - back the Bases' power down so you are not pushing the swing too hard and you may even want to track how well the power supply on the amp is keeping up with the power demand. This is why people used to run batteries' behind the power supply to boost amperage the amp seeks from the sagging power supply.

Ok I'm pretty much done, I just wanted you to get the best foot forward when you get started. As you experiment with the setting of power and ALC/AMC and the operating voltages between the two - you will find that the Base can run cooler and better if just kept a little bit less than max rated power supply voltage. The amp will do better if it's allowed to have a little extra room for itself when you place a demand on it - hence the variable voltage to set the amp so it can take the SSB signals and run them more linearly and when it needs to run Class C - the boost in voltage will help the map complete the cycles better.

I just want you to have a good experience with your new setup and enjoy the learning curve it gives you and the fun you'll have between the two.

 

[red97k1500]

I was looking at a classic 142GTL for a decent price. Has extra channels, unlocked clarifier, keys 4 swings to 9, does about 20 on sideband. Supposedly just tuned and aligned.

Never had a base rig ever and have been eyeballing these for awhile. I read VR6 can turn down the AM power so I can setup for an amp.

Anyone run a 142 with the mini KL-203 AMP? Wondering is the 203 or like the newer 7505v would be better?

Ask, what is the warmup time for a 142 to be on freq for sideband if it's a "good" one??

I have never owned a 142gtl, but I do have 4 radios with uniden pc385 boards in them. 2 140 gtl’s and two old school 8719 McKinley’s.When used inside my house there is no noticeable warm up time for me. I live in Texas maybe if I left them in the truck on a really cold nite there would be a warm up time, I have found these radios to be very stable on frequency. In my opinion they are great side band radios. I would take a 142gtl or uniden Washington over any currently made radio, but that’s just me.

 

[CB590]

@Andy. I planned on using a separate power supply for the 203/7505v. But I see your point on the amperage.

 

[kopcicle]

sent a PM but have more...