Cobra 19XS AM power ??

[CB590]

This was my first rig back in like 83-85. I was like 13.

Was interested in getting one for nostalgia and possibly running with my KL203 amp

All I see online is cut 105 for modulation. That's not what I want.

But I would like to adjust the AM power down abit to be at the 2w or so mark for the 203 to play nice and not burn up.

Anyone have any info on this or a pic of the insides of one they may have in a junk pile?

Photo for reference.

 

[TM86]

This was my first rig back in like 83-85. I was like 13.

Was interested in getting one for nostalgia and possibly running with my KL203 amp

All I see online is cut 105 for modulation. That's not what I want.

But I would like to adjust the AM power down abit to be at the 2w or so mark for the 203 to play nice and not burn up.

Anyone have any info on this or a pic of the insides of one they may have in a junk pile?

Photo for reference.

View attachment 34969

I've still got my 19xs, I'll dig it out and see if I still have the schematic somewhere.

 

[Handy Andy]

See if these can help...

But look for the PLL chip make sure it's an LC7131 - which these schematics and stuff are based on...

 

[TM86]

So here's what I've found. Schematic is available online, as well as adjustment info. Throwing it all in here anyways.

AM power adjustments are L205, L206, and L207. L205 is a can that sits between the driver and the final. Final is that big transistor in the back of the radio bolted to the chassis on the channel selector side.

L206 and L207 are the two adjustable coils between the final and the SO239 on the back of the radio. They're big, and not in cans, so kind of hard to miss.

RV201 is the AM modulation adjustment. Sits near the middle of the board, so another hard to miss item.

If you happen to have or can look up Secret CB volume 18, page 51, there's a drawing in there that shows the relative positions of the coils and the modulation adjustment.

Secret CB Volume 28 page 66 has the schematic.

The Screwdriver Experts Guide has the adjustable parts listed. It's in Appendix F in my copy.

Sorry, no pics with arrows pointing to the right parts. Don't have things that together just yet.

 

[TM86]

See if these can help...

But look for the PLL chip make sure it's an LC7131 - which these schematics and stuff are based on...

Just curious, because these little cheapies were only sold for a few years, have you seen any with something other than an LC7131?

 

[Slowmover]

This was my first rig back in like 83-85. I was like 13.

Was interested in getting one for nostalgia and possibly running with my KL203 amp

All I see online is cut 105 for modulation. That's not what I want.

But I would like to adjust the AM power down abit to be at the 2w or so mark for the 203 to play nice and not burn up.

Anyone have any info on this or a pic of the insides of one they may have in a junk pile?

Photo for reference.

View attachment 34969

Pics of that 13-yr old or it didn’t happen

.

 

[Handy Andy]

Kraco had an older MADAY with just the rotary channel knob and no display - hand wired in - using a 7130/31.

I've got older "HELP" radios that use a C5121. and Cobra 19+ that also has that C5121 - they have a built in Display ROM support matrix for Segment to Display driver so you didn't need the Rotary Switch to handle Channel and ROM needs of Pin programming in the same assembly - these C5121's are rare but allows the user to use a channel UP/DOWN button method to change channels versus the rotary.

Else the TC9106/9 or the LC7131 types...NEC only did 28XX series which uPD also had their hand in it...

Does that help?

 

[sp5it]

Increase R220 to lower output power. Do not touch Lxxx cans.
Mike

 

[sunbulls]

I concur with Mike. This diagram shows the Location of R220. I would first try 100 ohms as my base. Then check your watt meter at that resistance to see if you need to increase or decrease the resistance any further. At that point you can add or subtract in small 10 ohm increments to obtain your desired output. Never de-tune coils or cans to lower output!

 

[Shadetree Mechanic]

We should be able to come up with a jp36 type mod with a capacitor and resistor. I would have to study the Cobra 29 schematic a little more to know for sure. This would allow you to set the dead key wherever you want and still swing to full power on modulation.

Edit: looking at R220, I don't think that is where this mod would go. I am thinking it would go in the next stage between driver and final?

 

[loosecannon]

from the schematic posted it looks like you can up the value of R225 to lower the deadkey and then strap an electrolytic across it so the modulation still couples through full strength.
LC

 

[CB590]

I don't work on radios (which sucks). If I were to get this I'd have to send it out. I'd probably send the 203 with it for proper adjustments.

I'd like 2w swing to 8w to drive the 203 to about 80-100 low with hope.

 

[Handy Andy]

This might help...


In the schematic, the thing uses Electret condenser Mic element powered thru Pin2 on the Mic Jack...

 

[Shadetree Mechanic]

A condenser mic, I bet it sounds good. Not too many radios come with those. Cool!

 

[Handy Andy]

I may have correct myself on this...

This thing may have a built in Pre-set mic amp - not sure...

There's little info about this amp...
But it does cross over to a KTA7217...​

Why is this important? The radio DOES NOT HAVE a MIC PRE-AMP.

Hmmm...- so to handle that, it needs some other type of power source and means to amplify...

So if the TOSHIBA didn't then that means back to Pin 2 I go...

This is the only proof I got so if it's wrong....
- refer to the Schematic and
My Appologies...
​

So if anyone else comes up with better ideas...or proof...
I'd like to know myself...

In the schematic, the thing uses Electret condenser Mic element powered thru Pin2 on the Mic Jack...

So you know, if you can't get a standard cartridge 600 ohm mic to work with this, think about measuring voltage at Pin 2 of the Mic - for Audio is sent in thru Pin1 - just can't find "return" for this setup...For Pin5 and Pin 2 short on TX if Plunger Diagram is correct.

Else if the other way of "normal" being the Common - Pin 5 - opens Speaker return... but Power from a line off of PLL20 (the RX/TX switch frequency offset stuff...) goes thru Pin 2 and 5? So it loosk more like this Schemo may have an error in the Mic wiring...