Locking the Clarifier on a 1st Gen 2970

[Xjeepguy]

But still no measurement of the radio's internal frequencies?

After all, that's what controls the output frequency of the radio.

Got in the habit of setting the two 10.24 crystals by monitoring each one separately, then setting the three 10.69x trimmers.

Last step is to set the "Tx" trimmer pot VR21 so it transmits on the same frequency as it's receiving with the clarifier centered.

The one thing that can upset the applecart is the mode switch. It has outputs feeding the CPU to tell it what mode is selected. This is how it offsets the PLL to match the change in carrier frequency for each mode. As a rule, if this is the problem the error will be exactly 2.5 kHz, since that's how much each mode shifts from AM. A noisy mode selector can make the frequency unstable. If memory serves, there is a separate plug from the mode-selector board to the CPU board. Could be a weak point.

73

I will investigate that mode switch , appreciate that info . It is around 2.5 yes

 

[Xjeepguy]

Jeff,

May I suggest a possible solution?

If you want the Clarifier to slide, here's how to do it correctly.

You have several things going on, the clarifier is putting out too different a voltage which is why you can't tune L27, L28, and L29. And the Alignment is off.

If you want the Clarifier locked, put the parts back together as in the schematic below.

To unlock Clarifier:

First lets look at what the clarifier mod should be:

View attachment 66015

View attachment 66016

View attachment 66017

View attachment 66018

Remove/clip D69 - this removes the TX voltage from the circuit.

Remove R197 - this removes RX voltage from the circuit

1K precision trimmer (Bourns) Preparation:
You are only going to need the middle and an end leg (doesn't matter which); cut one end leg off and bend the other end leg 90 degrees (sticks out).
Adjust Brass screw for 100ohms between the 2 legs.
Wire and insulate a 8" piece of wire to the end leg sticking out from the trimmer.

Where the bare wire of R197 was just below J118, solder the middle leg of the precision trimmer (connects to red wire on J118).

Make sure R198 is intact and not jumped - this helps you slide down

Make sure D61 is intact and not jumped - this drops the voltage .7v

Connect the wire from the trimmer to a constant, stable 8v source (8v pin of IC6 or IC16). Measure both to find the one that changes the LEAST between RX & TX and use that one (less than .02v at least).


Alignment:

You need a good 8 digit Freq. counter to do this correctly.

First adjust L27 for mid tuning range (screw the slug up or down).

In AM mode, while looking at the freq. counter, turn the clarifier until it reads 10.695000 MHz +/-10Hz or as close as you can get (don't worry about the clarifier position; we will take care of that later). Adjust the slug if necessary to get it exactly on freq.

Don't move the clarifier any more!

In LSB mode, adjust L28 for 10.697500 MHz +/-10Hz on the freq. counter.

In USB mode, adjust L29 for 10.692500 MHz +/-10Hz on the freq. counter.

This gets all 3 modes "aligned".


Next, adjusting the Clarifier for 12:00:

Measure the voltage on the wiper (center) connection of the Clarifier (Brown wire on J118) and note the position of the clarifier. Write that down. That is the voltage that needs to be output when the clarifier is @ 12:00.

Now move the Clarifier to 12:00. Is the voltage higher or lower?

If the voltage is higher, then the voltage coming out of the clarifier needs to be reduced. With the Clarifier @12:00, adjust the precision trimmer to match the voltage that you wrote down.

If you can't adjust the voltage down enough with the trimmer, use a 5K trimmer.

Rare - If you can't adjust the voltage up enough, start the "Alignment" process with the clarifier turned a little more CCW from the original position used the first time to "Align". Then just adjust L27, L28, and L29 for freq.


*********************Easier Method to Unlock Clarifier**********************
Basically using the existing VR21 instead of a precision trimmer.

Another option that is easier to make the clarifier slide is lift the leg of R185 opposite VR21 and attach the 8v source to it.

Remove D69 - this removes the TX voltage from the circuit.

Remove R197 - this removes RX voltage from the circuit

Make sure R198 is intact and not jumped - this helps you slide down.

Place a jumper in the hole where the anode end of D69 was (connects to VR21) to the hole left by R197 that connects to the red wire in J118 (right below J118).

Make sure D61 is intact and not jumped - this drops the voltage .7v.

Adjust VR21 to change clarifier voltage. It now has constant voltage instead of TX only.

The 5K VR21 isn't a precision trimmer so it will be more challenging to get things on Freq.


Good Luck!

Thanks a million for that info , it is very helpful , next time I pop the lid on that I am going to see exactly what someone else did inside .
What I really want is the CLR locked like it came from the factory and the radio back on freq. I don't know why people unlock these 2950/70 clarifiers . If you want to move up or 5 down just hit the shift and a few clicks right .
I'll post back here when I get a better look inside , thanks for the help .
Someone also had the SSB power turned way way down , got that back up 120 PEP , so that was one win

 

[Dr. Frankenstein]

Many argue about unlocking or locking the clarifier.

The clarifier is not the problem with your radio, the synthesizer circuit is and it needs to be tuned properly so that the clarifier is at 12:00 on all modes and on frequency (as Dr.Dx has stated). You already know that, but you're blaming the clarifier the most important knob on a working Side-band radio.

Once the synthesizer has been tuned properly the unlocked clarifier becomes a very fine tune knob.

When you use (adjust) a locked clarifier you're only adjusting your receive frequency and not your transmit frequency. You might as well super-glue the clarifier in place and never use it again ...... ever.

There are a lot of people who know how to use Side-band radios and would never want a radio with a locked clarifier ...... it's not about the 5Kc slide ..... that's a bonus.

It's about being on frequency and there are times when just a little bit is hard to get with a locked clarifier. You may disagree and it may not seem like a lot, but people still know when others are off frequency ....... especially when you have met face to face and have been friends for many years.

The last thing you want to hear constantly is: "Get on frequency!"

The last thing you want be be saying is: "Is that any better?"

To each their own, but why did that clarifier get unlocked?
Just like the chicken .... to get to the other side.
The other side being the Transmit with the and Receive.

73