President AX44

[Handy Andy]

Between the IF Gain control and TX RF meter setting - they should both be pretty close to mid point - but not all meters work like they should - some seem tighter in RX S-meter than say the older OEM one which drifts like a dinghy behind a Caribbean cruise ship - just lollygags along not really showing anything but "working".
IF you like the new meters "stiffer" results - how is the receive?

I'm asking because if...
- seem a little too quiet?
- perhaps the audio more comrpessed than you remembered.
What happened to what it sounded like before all this work was done?

It could be from the recapping and the tolerances the parts list to what you used may have been exact - but the response is different now. Because of the changes to the Basic Capacitor design during the time this thing had its last oil change.
​

So there are some "tweaks" you can do to it in its' stock form - being mostly the IF gain control and maybe a retune of a coil or two - - the only other way to adjust the "Meter seems Low" issue is to change some parts that will affect the receive performance - some might like it, others might hate it - so if you like the noise floor it has now, well, just live with it.

But if the noise floor seems too quiet and IF gain tends to overemphasis on the noise level - then AGC may be part of this problem. That is a simple fix or change of 1 part and observe the results - if you don't like it - revert back and understand you might not have much you can change...

The AGC "Resistor" that I'm referring to is R26 - schematically it's a 22K - RED - RED - ORANGE
This controls how much energy the Receiver sends back to the front of the section to control and maintain some leveling system of signal to Noise ratio when a receiver is wide open to fully immersed, for signal. level.

To many this part doesn't do much for them because IF gain can handle most of the conditions. But the quality of signal and the dynamics some signals will have - they get lost in the IF gain control being too limiting of range.

So there are the following components, resistor R26 (22K) - the AGC Cap C37 4.7uF (you can go up to 22uF or as low as 2.2uF) or the 455kHz IF Cap - C22 a Tantalum of 10uF at 6.3V rating - so the issue is not yet complete when it comes to a true recapping - you have to look back and realize the values used (back then) were for a specific outcome due to the tolerances the parts they used in the assembly of this thing - was one value - but you just put in similar parts but of different reaction in capacitance characteristics you didn't expect - it's not anyone's or anything's fault. Only understand, they act this way because of the internal structure of the part is different and the circuit was originally designed to work one way with this part - but now acts differently.

This is normal.

 

[Smokinone]

Between the IF Gain control and TX RF meter setting - they should both be pretty close to mid point - but not all meters work like they should - some seem tighter in RX S-meter than say the older OEM one which drifts like a dinghy behind a Caribbean cruise ship - just lollygags along not really showing anything but "working".
IF you like the new meters "stiffer" results - how is the receive?

I'm asking because if...
- seem a little too quiet?
- perhaps the audio more comrpessed than you remembered.
What happened to what it sounded like before all this work was done?

It could be from the recapping and the tolerances the parts list to what you used may have been exact - but the response is different now. Because of the changes to the Basic Capacitor design during the time this thing had its last oil change.
​

So there are some "tweaks" you can do to it in its' stock form - being mostly the IF gain control and maybe a retune of a coil or two - - the only other way to adjust the "Meter seems Low" issue is to change some parts that will affect the receive performance - some might like it, others might hate it - so if you like the noise floor it has now, well, just live with it.

But if the noise floor seems too quiet and IF gain tends to overemphasis on the noise level - then AGC may be part of this problem. That is a simple fix or change of 1 part and observe the results - if you don't like it - revert back and understand you might not have much you can change...

The AGC "Resistor" that I'm referring to is R26 - schematically it's a 22K - RED - RED - ORANGE
This controls how much energy the Receiver sends back to the front of the section to control and maintain some leveling system of signal to Noise ratio when a receiver is wide open to fully immersed, for signal. level.

To many this part doesn't do much for them because IF gain can handle most of the conditions. But the quality of signal and the dynamics some signals will have - they get lost in the IF gain control being too limiting of range.

So there are the following components, resistor R26 (22K) - the AGC Cap C37 4.7uF (you can go up to 22uF or as low as 2.2uF) or the 455kHz IF Cap - C22 a Tantalum of 10uF at 6.3V rating - so the issue is not yet complete when it comes to a true recapping - you have to look back and realize the values used (back then) were for a specific outcome due to the tolerances the parts they used in the assembly of this thing - was one value - but you just put in similar parts but of different reaction in capacitance characteristics you didn't expect - it's not anyone's or anything's fault. Only understand, they act this way because of the internal structure of the part is different and the circuit was originally designed to work one way with this part - but now acts differently.

This is normal.

Receive is good, a little on the hashy or noisy side, but not to the point it much out of line with my other radios, and strong signals override it, weaker signals get a little lost.
I will look at the tant (C22), I have some higher voltage of the same value so it will be a good idea to replace it just for good measure.

I really didn't listen to it before I recapped it, so I don't know how it sounded before. Seems a little more towards the treble than bass side. I wonder if D4 and D5 to 6236 diodes would make much of a difference.

Thanks HA.

 

[Handy Andy]

You're quite welcome, always appreciate how someone wished to hold onto a piece of history - in some ways - older than some out here on the net that repair such things...

Not to give away my age...

Let's see the Empire State Building was built in ... Too old to remember that... But it was done before my time (I think).

You'll find that these older radios actually did better using equipment and parts from their time. Schottky was not available for them back then, so they used older Silicon and Germanium which have a nicer warmer sound to them than a harsher Schottky which actually introduces more noise than it fixes.

So if Schottky was the only thing they did to try and upgrade it, sorry to know that...because I could have helped direct you even further to other receive mods that would have helped if the tone was going to be too high...

But I will post this also remember too this affects signal strength...to a point - but in that radio is a special cap used on the Receives' output line just before it makes it to the Volume control...

If you have the PC-901 board in it - that resistor / cap combo might have an extra part already installed on the foil side of the board by the output of the 270K Resistor (R15) - They used a typical 223 to a much as 473 Disc cap here to change / adjust drive and tone - this cap straddled two pads that took Detected ANL filtered Audio and routed it up from the board to the Volume control with the other side (middle lead) heading off to the Meter side of the board front by TR10 - C151 (222) and C54 (223) Between those two leads one was ground for that pot and SQ, the other leg went off from there to squeeze in between C54 and TR10's location.

So that was your "tone" point if you needed one to change the tone - any sort of cap placed across the wire soldered to the pad that goes to the Volume control from here to foil ground at the edge or by IF Gain Point VR2's Foil board ground here - lowers the "receive hiss" and reduces drive "level" so if you're encountering "blaring" caused by overdriven mics from signals too close to you - you can use this little spot to your advantage.

If you're working from a service manual of some type - remember too that; as they made this radio - they did several on-the-fly changes to the values in specific areas of the board that seem subtle but they were undocumented changes that never made it to the list. If you found several values "off" to the parts list, the value stamped on the part in the spot is the one it needs to be.

 

[Smokinone]

The only mods, if they are, is that the L13 and L20 inductors have the core or slug missing. At least that's all I can find. The driver and final had been changed out at one point, but they are the same as the originals. I know this radio has been sitting around untouched for at least 20 years.

I am glad you told me about the diodes, I didn't know how they would effect things. I am trying to learn all I can, and you've been a great help. In fact, there are a few other radios around here I might try and tackle. The ANL seems to work pretty good at quieting down or minimizing the hash.

It is a PC901AA board, and has nothing under the R15 on the solder side. I am using a SAMS CB-207, which is for the Cobra 25GTL. There are some differences, seems a few components missing from the President board compared to the Cobra version.

On a quick note, I did change the tant, C22, and adjusted a little bit, and the meter seems to be behaving more like it should. I have been getting a lot of noise lately, but I think it's better. I'm at a kind of a lull here in the usual noise, and the meter is about where I would expect it to be, with it peaking near the red line at the upper end of scale. I know they're not that accurate, but it was behaving a little different than I thought it should.

I"ll run it a while, but I am going to look at the suggestions you made and look at the radio and find the points mentioned and see what happens.

Thanks...Again

 

[Smokinone]

There is one thing I am curious about. This radio doesn't have a VC1 to adjust frequency. This radio sits at 27.18438 for channel 19 so it is off a bit, but I see nothing to adjust that. The Cobra manual shows VC1 adjustment to correct this.
I don't have the correct manual for this and don't see anything that would adjust to get at the correct frequency.

I have 10.23973 at pin 2 for my 10.240 X-tal

Or am I close enough do you think?

Thanks, just trying to educate myself.

 

[Smokinone]

I think this has it covered.

https://www.worldwidedx.com/threads/uniden-pc-66-xl-no-power.229497/page-8

Thanks

 

[Smokinone]

If you have the PC-901 board in it - that resistor / cap combo might have an extra part already installed on the foil side of the board by the output of the 270K Resistor (R15) - They used a typical 223 to a much as 473 Disc cap here to change / adjust drive and tone - this cap straddled two pads that took Detected ANL filtered Audio and routed it up from the board to the Volume control with the other side (middle lead) heading off to the Meter side of the board front by TR10 - C151 (222) and C54 (223) Between those two leads one was ground for that pot and SQ, the other leg went off from there to squeeze in between C54 and TR10's location.

So that was your "tone" point if you needed one to change the tone - any sort of cap placed across the wire soldered to the pad that goes to the Volume control from here to foil ground at the edge or by IF Gain Point VR2's Foil board ground here - lowers the "receive hiss" and reduces drive "level" so if you're encountering "blaring" caused by overdriven mics from signals too close to you - you can use this little spot to your advantage.

To be sure on the placement of the cap you mention here, I have a photo of the area that i think we are talking about. A 223 to a 473 cap at the point I have marked out.

I'm sorry to be a pain, but I tend to doubt my abilities to understand sometimes. I don't want to goof up anything that I have already done.

Thanks

 

[Handy Andy]

Woof, actually you would have seen it stand out...

You don't, it wasn't installed - but the cap for the TONE is here, where you highlighted in Violet...

​

If you notice - there is a SEPARATE set of PADS - you're using one hole for your "audio tone" mod - that is part of a TX switch section that uses this trace as a board foil ground for another radio design as they produced these. Those two open pads - one side is TX power - but where one leg of your cap goes, is a Board Foil to Chassis foil Shield RF bypass cap - which if installed can work in your favor if you run into headaches with Power Mic and squeals. This is Board Foil Ground your attaching the opposite leg to - this is board ground. The other leg of the cap rest with the wire, and R15 output lead to this wire.

To complete this - the ANL switch also shares tight space in this area - so I've "blown it up" and identified the possible trouble spots for you so you don't mis-wire this.

 

[Smokinone]

I think this has it covered.

https://www.worldwidedx.com/threads/uniden-pc-66-xl-no-power.229497/page-8

Thanks

So I dropped a 68pf cap into C111, which was a 47p (49p on the tester), and the frequency dropped a bit. That is the only value I had in a NPO/COG cap. I think I will try and order a 33p and see if that gets me closer to where I want to go, and see if a lower value gets me the higher frequency. Just playing around, trying to learn what works and what doesn't...

This board doesn't have the holes for VC1 as the PC66 in that post, and I don't think I have the correct value varicap anyway. I don't really want to drill anything.

 

[Smokinone]

Woof, actually you would have seen it stand out...

You don't, it wasn't installed - but the cap for the TONE is here, where you highlighted in Violet...

View attachment 48155
​

If you notice - there is a SEPARATE set of PADS - you're using one hole for your "audio tone" mod - that is part of a TX switch section that uses this trace as a board foil ground for another radio design as they produced these. Those two open pads - one side is TX power - but where one leg of your cap goes, is a Board Foil to Chassis foil Shield RF bypass cap - which if installed can work in your favor if you run into headaches with Power Mic and squeals. This is Board Foil Ground your attaching the opposite leg to - this is board ground. The other leg of the cap rest with the wire, and R15 output lead to this wire.

To complete this - the ANL switch also shares tight space in this area - so I've "blown it up" and identified the possible trouble spots for you so you don't mis-wire this.

That's the ticket. I put a 223 ceramic and it cut down the hash high tone. I'll have to listen a while to see if it effects the receive. I am getting better tone from nearby stations as far as voice quality so this was a win. I don't see any need to go to a 473 at this point, but maybe later. I'm in training.

Thanks a bunch HA. You have more knowledge on this radio stuff than I can imagine.

 

[Smokinone]

So I dropped a 68pf cap into C111, which was a 47p (49p on the tester), and the frequency dropped a bit. That is the only value I had in a NPO/COG cap. I think I will try and order a 33p and see if that gets me closer to where I want to go, and see if a lower value gets me the higher frequency. Just playing around, trying to learn what works and what doesn't...

This board doesn't have the holes for VC1 as the PC66 in that post, and I don't think I have the correct value varicap anyway. I don't really want to drill anything.

Well, the 33p cap went farther off than the original 47p. I dropped in a 43p and the results were much better. C111 is the cap for reference.



pin2 for the 10.240 went from 10.23973 to 10.23998
output at SO239 or antenna output went from 27.18438 to 27.18499

I don't think I could get any closer

I know nobody will know the difference, but, I'm trying to get a grasp on how all this stuff works. I look at where the cap is in the schematic as to where it is and what it does... hopefully my CRS doesn't interfere with my learning process.

Thanks HA

The way things are working out I may get the nerve to try some SSB radios I have that don't quite work the way they should.

 

[Handy Andy]

I see you're having fun!

Congradulations on your success.

We (all of us) are here if you have questions!

Best of all, enjoy your radio!

After all it's on frequency.