Cobra 148 GTL clarifier unlock.

[Low_Boy]

Bad weather?

Drive Safe...

Thanks Andy i am local just too many hrs.

 

[Handy Andy]

Hey, stop on by and take care of mom - she's easy enough to deal with - only difficulties are bathroom potty and feeding her...

Else - she sleeps...pups nap right along with her...makes for a boring day - all other chores are done!

I'll do your job for a day...

 

[Low_Boy]

Andy they surprise me home early but have to work tomorrow. Changed R149 to a 47k resistor. Was able to bring L23 and L22 which were good anyway a little firther up in there travel. Still dead on freq. This put L59 at 34.7660/1 teetering MHz just a bit off from spec. Put the 40ph in CT2 zero beated CT
2 and it sounds good on usb. With clarifier center. Thanks

 

[Low_Boy]

By the way there is no capacitor in L59 I took it out and looked at it. Also putting the 40pf where the cap should have been on the underside of course did about the as changing R249.
Also tried it out over the air and was told usb sounded right on.
We kind of tricked it in to working.

Correction R149.

 

[Handy Andy]

Yes, there shouldn't have been one, what I was referring to, was how they use L59, L58 and R146 as the other half of where the Xtal completes it's circuit - C119 Blocks current flow (DC) from passing thru L22 and C120 blocks L23's ability...they all "float" except for L59.

So good to know you got it working - enjoy that radio!

 

[Robalo]

yes enjoy the radio ! NEXT radio

 

[Low_Boy]

My next radio will be a hard one. I can't remember the model number but it is the General Electric AM sideband radio mobile unit with two boards. I guess it is the Super Bass But the mobile version.

 

[Low_Boy]

I have to correct my post. Changed out R149. So Andy what does this R149 do? I was told along time ago that if the radio would not align cut R149. I never liked the idea of cutting anything so I came up with thit value a long time ago.

 

[Dmans]

I can't remember the model number

I guess it is the Super Bass But the mobile version.

Sounds like the 3-5825B. Nice radios!

73's
David

 

[Low_Boy]

Sounds like the 3-5825B. Nice radios!

73's
David

Just looked at it. That is the one.. It looks like it has been sitting for a long time. Has big problems No TX Very little RX. Does not even show TX with a radio sitting next to it.

I do not want to derail my own thread but I am sure once I get in to this I will possibly have a problem that is too big for me to figure out.

 

[Low_Boy]

This post may be too old to edit. So I screwed up. What I replace R149 with is a 47K 1/4 watt resistor.

Somehow I screwed up in previous posts and have posted I replace it with a 40pf. Wrong disregard that.

 

[Handy Andy]

I have to correct my post. Changed out R149. So Andy what does this R149 do? I was told along time ago that if the radio would not align cut R149. I never liked the idea of cutting anything so I came up with thit value a long time ago.

Wow I missed this...

Gotta get FRESH stuff to review...

R149 is the "stabilizer" of when the RX and TX lines switch and the D52/D51 diodes are in place.

When you look back at the Voice Lock control - there are 3 resistors used - two arrive from 8 volts - a 3rd goes to ground.

Ok, for an experiment for you someday is to do that very "variable" circuit - but look at the output (wiper arm) - you'll see it is not the BEST at stability - for as your rotate the knob, it tends to stay more Positive - doesn't really drop below 3 volts - it's is designed for this - the Varactor it adjusts has the best linearity between 5 volts to about 3.2volts - a pretty narrow range - but it is OPERATING in it's most linear region.

Ok so why R149 - to provide a KNOWN load.

D51 and D52 - keep current and the power consumed - CONFINED to the Tuning Circuit.

Once you clip D52, no TX voltage.

Some bypass D51 - which is a no-no, puts Voice Lock interactively with R149

• - for R149 is the proper load resistor on the circuit to draw in the power from either TX RX to KEEP LINEARITY of tune from Center slot above and below
• - kinda critical for many wanting to retrieve drifting QSO's
  • - or as needed, locate them.
• - D51 stays in - to work the Center Slot Linearly - IT MUST because
  • - allows for Steady state CONSTANT load to stability and reduce drifting
  • - don't bypass D51 - else LOADING changes R149's ability to provide stability
    • and Voice Lock now becomes a LOAD and both of them work against each other
      • - causing even more drift and EXTRA SENSITIVITY to voltage swings
      • - which is what you DON'T want.

The Varactor needs to work in a High impedance circuit so it works best when it's not loaded down with the Voice Lock impeding power flow - use D51 (please!) it keeps the power flowing INTO the circuit - not back out.

It may seem like I'm backpedaling, no I'm not.

In the past - I answered questions regarding the RANGE of tune to twist into center of the channels from Center Slot

• - a deep drift requires a different approach

As well as other questions like - how to keep the radio working with an open clarifier and yet stay close to center slot to help find QSO's as well as stay with AM traffic as needed

• - Voice lock works all the time - not just SSB.

So I have reasons to answer with many options, that some work well for MANY, but not ALL, SOME work well for the SPECIFC application - but cannot work for (again) ALL.

Other ideas help to keep people from losing interest in SSB and bail out of another method of radio that can prove quite useful.

 

[Low_Boy]

So looking at the schematic R149 goes to ground.

 

[Handy Andy]

Now look at D52 and D51 - it stops the flow of P____ from leaving the C______ so the V_______ will be able to operate L_______ thru it's tuning range.

Fill in the Blanks...using these letters
AEIOU - WRCTNLY - some may need to be used more than once...

R149 goes to ground because D51 and D52 prevent loading from external sources.

Clues?
tOWER
haIRCU_T
cOntRACTOR
wINEAR_Y

 

[Low_Boy]

I will fill the blanks in tomorrow.
I know the V______ already. Lol. I know that goes to R149