To help you....
Using the info from the AM regulation section in the above posts - you'll see Q56 adds a level of complexity.
The thing is supposed to "pinch off" the envelope peak energy - but if your radio has a lot of modulation - it turns out way too compressed - the effect turns more into back swing with "clipping" and many wonder why that feature is even in there.
Anyone whom still has a CBT link - you can find this...
That is what makes it variable - and if you have time - sometime - an old Connex 3300 or even the Galaxy 33 can show why I said what I said back in the days of CBT and why I posted something about the AM Power pot in the PC-122 Section - to see the evolution - someone learned something from those days.
But did they "steal" intellectual property? No, because they could have done a better job of fixing the problems by making the VR "variable" - not so variable - just place the darn thing in a divider circuit with a resistor of values in range to reduce the "drive" and yet allow for AMC and ALC - yet deliver a lot more audio so you did not need to delete the limiter. This circuit if used right, actually helps with that.
At least give the Audio that can't get squeezed in there...
A place to go.
People emailed a lot of times asking why I went thru so much trouble to show this.
I simply replied that if you look at it, the lower the rotation gets to the Ground lug, the LESS forward bias is there for Q53 (Galaxy) and will oftentimes make the audio power envelope appear to swing backwards. Too much signal - not enough bias - so no power - result = distortion.
The "dip" is resistance (or the change) was to demonstrate that the range of rotation affected the drive - thru the way the regulators BASE lead accepted power.
- In the "setup - the Rotation index notch was set here, and you get this result from the limiter.
- When you dipped it down, the carrier dropped - just a little.
- Go back to your Mod meter and now you will see this close if not over 100% mod effect
- So why this little change for a bigger effect at the AMC?
- Becasue...
- Q53 (Galaxy) Regulator was still acting like an amp - so it can take the audio from the Base and amplify the signal with more headroom - to help with the dynamics.
- The Divider add-in helps to reduce the dynamics by changing the amount of power the Bias window has.
- So, the amplification will be there, you will have less swing - but the audio clarity is preserved.
If you wanted to sound cleaner - you needed to have some forward bias, the upper and lower resistors R263 and R263A - work as a window to float the wiper arm above ground. Providing the Base some forward bias - reducing the clipping and the distortion effects. R264 limits the current yes but doesn't offer any solutions for audio swing power to exit, so R264 is altered to increase it's presence therefore forcing the audio drive dynamics to be less.
To bring in the Swing, you INCREASE R263 - to a value to let you enjoy the effects. The 100Ω value shown is arbitrary. I was just too lazy to edit in the values - so I'll give you a range to work with so see if it helps you obtain that which you seek.
- Range?
- Resistor R263 has to be a GREATER value to R263A
- R263 - Between
- 100Ω - Minimum Lower limit
- 680Ω - Working upper limit
- You don't want to "starve" the amplifiers' ability to handle all the audio arriving.
- R263A - Between
- 15Ω <- Recognize the Value? This would be the lowest to reduce the distortion effects
- 47Ω - Upper limit to allow the pot substrate to drain thru to ground to keep the value from lifting voltage too high.
Doesn't seem all that much, why even try? Well, you don't have to, just understand the values above and the concepts behind them are going to be used against us someday when they produce radios "en - Batch" that we will have to know what they are up to as they try and limit radio operational "faults" before the ones the produce these contraptions called radio - are told - forced out, of the business because of the interference within the spectrum we're trying to keep alive - BEFORE they take it away forever.
Right now, VR14 divider shown 100Ω and 47Ω - gives the pot 1/2 to 1/4 LESS adjustment range (which is why I'm not making too many fans of the mod at the moment) But that is due to the INPUT power that arrives - just increase the upper (R263) value to LESSEN the voltage present at the center of the Divider or VR14.
R264 also has to be LOWERED to 2.2K to have any help here.
Your bottom resistor is your "holding lower-carrier limit" but the upper sets the Regulator Amp ability to actually be an AMP not just a regulator.
The impedance range of adjustment - when it comes to Audio - is affected, so the DC Bias range or Bias window is the two resistors R263, and R263A - while VR14 then affects the voltage component by changing the dynamics of audio - which can help you in limiter action - when there is no limiter
- Questions from the Back....
- Why not NPC?
- I never said anything about it. You CAN use the NPC mod and this at the same time.
The reason you have had the "biasing" problem was partly due to the level of voltage presence was between the Drain to Source potentials. The feedback paths between the Driver and Finals own "resistor feeder" to the Gate - they don't use Ferrite Beads (for a reason) but the impedance was not enough to tame the trigger. The Extra spike in voltage
From The AM Regulator got past and into the Gate circuit. By that Gate Circuits Tap - with audio Noise present - there's the ballgame.
Audio dynamics unless you're riding the processor - lessen the resistance.
- I'm not making Fans with this mod, only showing more of what I wanted to cover at a later time - this thread brought up that memory. So, in a way, you gave me an opportunity to help in having a teaching moment.
The changes - makes the audio less dynamic - but helped with the clarity. Less saturation and you didn't need a limiter so much as ones that kept this form of function stock and just pulled down the power from VR14 to lower the carrier to a point where you had more Dual Sideband operation than actual forward power.
Ok, it's your friend's radio - but to help others achieve a little more clarity with less splatter - you still need to drive the Regulator side with (
just a little) more bias - the above is only representational. So, no inquiries please about the reason for it.
I just feel bad that you encountered these biasing problems which adds to the reason the mod above was even shown back in those days.
Your changes to the AM power levels - and the addition Q56 to control the peaks of the envelope for that "power setting" helped me to understand this better so in this post I'm only offering some breadcrumbs to help you along the way.
Good job!
