Cobra 2000 GTL Lites

[whiteastro]

Yes, you'll need similar lamps to fit the "mounting hole" for RX and TX lamps - they use the same type.

Most usually choose 7371 - which is a 12V type - but they use of a dropping resistor of 47 ohms, puts the bulb filament requirement between 8V to 6V - with 6V being pretty bright and hot. While 8V gives you more even brightness, but 10V types gives you longer life and the colors are more saturated.

IF you plan on running 14 volts or more out of a power supply for this radio - (not recommended) - you might want to choose the 7371 (12V) it's safer but lower brightness will handle the higher voltage.

It seems to be the main reason why most repair - in the shop moments - are for when the user try's to get a few more "ghost" watts out of the radio by turning up the power supply voltage.

These things are fed thru the 13.8 Power supply rail and use a dropping resistor

Increasing that voltage applies more voltage to the bulbs - this shortens the life the of bulbs by at least 50% of their expected life - and on top of the heating that bakes the decal stencils that are non-replaceable - you have to use a photocopier / transparency method to develop the transfer and the inlay - and cut to size to get the Receive Transmit On-Air to look right.

I'm sure I'm missing something here. You keep talking about running a power supply with this radio, but I will be running it AC power because it is a Base Station radio and have no intentions of running it on DC power. What size Voltage bulbs did it come thru the Factory with, that's the ones I want to put back in it. Forgive me for not understanding the technical part My area is more the mechanical. I just want to put it back to the way it came from the Factory. Thanks !

 

[1iwilly]

all the bulbs say 11.65v at 45ma hope this helps

 

[whiteastro]

all the bulbs say 11.65v at 45ma hope this helps View attachment 46426

Thanks Guess I should try to take the time to read the schematics. So looks like if I put 12 Volt bulbs in they might not be as bright but would last longer. I read my Dosy meter more than rely on radio lights but want them to all work in case I have to sell it. Thanks again. Happy DXing

 

[Handy Andy]

There is part of the problem, this is not easy to answer...it requires a little math and understanding of ohms law to make it work.

And is why I ask about external power supply - some operators do this to provide the regulation and current for their MODIFIED radio - if you wish to stay stock - and wish to use the internal OEM one, then by all means continue to do so.

You have most of the answer as what is present to draw from - 11V if you draw at 45mA - know of a lamp that is close? Only the 12V or 10V types.

The crux of the problem, is in the filament itself - when a bulb lights up - you send power to it, it will drop votlage across it and consume current in the process, the bulb filmament continues to heat up and brighten until the resistance of the element itself becoems so great that it now CONTROLS the amount of power that flows thru it.

As long as you maintain the same voltage - that bulb will use that voltage to maintain a level of current to consume.

They installed resistors - which DROP voltage and current - which now changes how the bulbs will work in the circuit.

So they "rate" as if you measure here, at this spot - you'll see 11V but the IF the bulb draws 45mA - look at the chart...

Your best choices are 7344 - 7367 or 7371
All due to the DRAW in mA shown
AGAINST the best brightness (heat) factor (Lumens)
Also the LIFE it's Number Of Hours at that DRAW​

 

[whiteastro]

There is part of the problem, this is not easy to answer...it requires a little math and understanding of ohms law to make it work.

And is why I ask about external power supply - some operators do this to provide the regulation and current for their MODIFIED radio - if you wish to stay stock - and wish to use the internal OEM one, then by all means continue to do so.

You have most of the answer as what is present to draw from - 11V if you draw at 45mA - know of a lamp that is close? Only the 12V or 10V types.

The crux of the problem, is in the filament itself - when a bulb lights up - you send power to it, it will drop votlage across it and consume current in the process, the bulb filmament continues to heat up and brighten until the resistance of the element itself becoems so great that it now CONTROLS the amount of power that flows thru it.

As long as you maintain the same voltage - that bulb will use that voltage to maintain a level of current to consume.

They installed resistors - which DROP voltage and current - which now changes how the bulbs will work in the circuit.

So they "rate" as if you measure here, at this spot - you'll see 11V but the IF the bulb draws 45mA - look at the chart...

View attachment 46430

Your best choices are 7344 - 7367 or 7371
All due to the DRAW in mA shown
AGAINST the best brightness (heat) factor (Lumens)
Also the LIFE it's Number Of Hours at that DRAW​

Thanks again for the help because I have had no electrical training only bits and pieces I picked up along the way. Looking at your last chart it make me think maybe my best choice might be # 7367 because of Lumans and Life. I'm almost 71 YO. how many radio hours do I have left in me and the 7367 has better lumans than the other 7344. Next I have to go to their web site and check availability to see which I order. I understand decisions aren't always easy because I come from a maintenance background and every field can get technical. Thanks again !

 

[Handy Andy]

It's ok, one of my biggest fears is due to this lack of understanding.

I was simply getting you the information you need - with some basic reasoning as to why - but not into a long dissertation needed to clarify - did you want these to be little night lights or just keep the meters lit in low light situations?

There's a big difference.

Most whom switch to LED have dreaded the fact they even got talked into it for it tends to brighten the display, but also diminish the colors.

Which brings up another point...

White LED's emit predominately in blue, but use a coating that emits Red and Green - which changes our perception from Blue to a brilliant white (rated in Kelvin of surface brightness - about 6,000K - surface of the sun sort of thing) because Red and Green (in our eyes) see them mix together to form a bluish white light.

When these are placed in a typical meter made from the dyes of older times - the Red and Green are not perfect and the Blue tends to make more of a CYAN appearance that makes the Old-Style radio - look like you hid Casper behind the panel and are using it's glow to shine thru - fine I guess, but those RED LED displays make this look like a partially mutilated throwback to Back to The Future...

They didn't have BLUE LED's at the time they made this movie guys...
​

This mix is missing one main ingredient - Amber

So now you can have a Pallet of choices in LED but still - the spectral limitations of each "Kelvinator-Kolor".

​

Although we used RGB in CRT's and even Flat screen LCD - but they now realize that a "warmth" is needed - so they are using coatings that take the brilliance of the blue - but also mix the Red and Green of old, with Amber dyes to make the LED appear warmer - which actually is lower on the Kelvin scale - about 2300K to 3000K degrees Kelvin

• - see where this goes? I have to give you EVEN more information than you need to clarify that which you already knew.

You want to keep the lamps, the old style which it's made for and from that era...

But what occurs is when you get TOO much information - even more questions that I don't mind answering...

But

• do they provide help?
• Or only serve to confuse and obfuscate even more?

Hence

• - if not properly addressed - YOU WILL WIND UP FRUSTRATED

There's a lot to be said about Radiation - Radio or otherwise - including Light we see...​

I'm just trying to allow your experiences and enjoyment to continue without having to go into the physics of the thing...

​

 

[whiteastro]

Just basically to make the meters readable when you have the radio turned on and key the mic. I already put new meters in it which the seller provided but he didn't say the lights didn't work. He also said the radio was unmolested but when I got it I found it had Extra Channels installed so I'm hoping there is no more surprises. Everything seen to work good except the non-working lights. The radio is clean and in nice shape just needs the TLC.

 

[Handy Andy]

I hope the information can help.

IF the lights are not too expensive for you, buy several of the different types.

Why? Well, some lighting, like the meters, in OEM - were pretty bright, had a large face so needed a bright bulb.

They put resistors - of different values - in line with the bulbs to handle some of this uneven brightness demand to make the radio look "normal" at night. At least more equal.

Example

And yet they used...
​

• Cobra 142 - only used 2 bulbs for the meter lights but LED for TX and RX.
• - and in using those bulbs for the meters only sourced using 1 resistor
  • - this generates a problem when you swap out bulbs of different types
  • - one will suck up - take in all the power to run itself leaving the other bulb dark.
• To remember, there's nothing wrong, just the resistor and current demands of the bulb being replaced, is different - so it upsets the apple cart of power distribution - changes the power flowing - one now takes all the power and the other one cant heat up the filament enough to be seen.

When you replace lamps in any radio - unless there its only one bulb used, they recommend you change them all to reduce the "differences" in illumination as well as nearing the end of their service life - - each lamp is "tested" but when you no longer have the original source of supply - the different makers supply these, make these, types of replacement lamps to suit - however they will offer variation of lumens and power requirements for their installation.

What I'm trying to say is, be flexible - put your needs to it, not someone else's - make it your own.

 

[whiteastro]

The JKL company wants you to buy a pack of 20 lites for $25.00 so I won't be buying variety. But I should have enough to replace all the lites. Did a radio test today, had my Old Cobra 2000 GTL set up side by side with my New Galaxy DX 2547 on the same antenna. Both on 38 LSB. First turned on the Cobra to check for DX and Florida was banging in like they were in the room. Turned off the Cobra and turned on the Galaxy and the Cobra beat the Galaxy Hand Down for receive, Sound & Signal strength. Was a simple test maybe not scientific but that is why I wanted to buy a Cobra 2000 GTL because I believe in Cobra's Receive circuit. I've tested other radios before and it always seems as if Cobra comes out on top. Just My Humble Opinion !

 

[Handy Andy]

it always seems as if Cobra comes out on top. Just My Humble Opinion !

You're in a boat with a lot of others whom feel the same way.

The Realization of when...
Having Older Radio Equipment That Still Works - Matters​

 

[whiteastro]

Last night I walked by my radio room in the dark and I could see the dull glow of CH.38 even though the radio was turned off. What causes that?

 

[Handy Andy]

Older bulbs still present or are they burned out?

As they burn out, they are taken out of circuit.

The Radio still has a live feed to it for the Clock / Alarm - keeping the displays "idle"

Part of the channel display being a ghost image can be found a partial if not complete answer in these threads...
https://www.worldwidedx.com/posts/607211/
https://www.worldwidedx.com/posts/691222/
https://www.worldwidedx.com/posts/725272/

Deals with the power switch lifting ground from the CB board, but not the rest of the system - turns off the CB side but the meter lights are wired to ground thru a portion of the circuit that is still tied to main Power Supply Ground - when the meter lights burn out - the CB board to ground potentials begins to change - starts to use the LEDS to supply part of the ground return in an attempt to equalize "ground path" potentials. The Switch may be Off - but that doesn't Mean Ground Gives Up That Easily - type of scenario - makes a good scary movie effect to say the least.