GE Superbase LSB transmit freq off

[Lkaskel]

Hello Gang,
It's been a while since I have been at the bench. I have a GE Superbase that I have re-capped and aligned. I am having one issue aligning the LSB transmit freq. It is 150HZ high at best. AM and USB are dead on. When I adjust CT2 for transmit offset it will range from 600HZ high down to 150HZ high. Any thoughts? The clarifier is not unlocked. I am injecting a 1KHZ signal at the mic input for USB and LSB.

Once I get this straight then I need to figure out the AGC. It is an interesting alignment challenge.

Thanks as always for your kind replies!!

Larry

 

[oldtymer]

Crystal aging?

 

[999]

Crystal aging?

If it were the crystal it would effect everything, not just one mode.

 

[oldtymer]

If it were the crystal it would effect everything, not just one mode.

In many of the older radios there were crystals for the carrier freq. and one for each
side band offset.
I don't know if this model has that layout but the OP asked for hints & that's what I
posted. If that oscillator is referenced to it' own crystal that MAY be the reason.
A trimmer cap for the crystal might fix it if that is the cause.

 

[999]

This is an 02A pll radio.
http://www.cbtricks.com/radios/general_electric/3_5875a/graphics/3-5875a_sch_pg1.gif

 

[nomadradio]

The radio has a separate trimmer cap for each sideband on the carrier-oscillator circuit. One crystal 10.695 MHz crystal X1, two trimmers CT1 and CT2.

The PLL has a 10.0525 crystal that also has the same two trimmers, one for USB, one for LSB.

I'd have to dig out Sams CB series volume 234 to get more specific than that, but those four adjustments almost never remain perfectly stable for 40 years. Only way to tell if a crystal has "aged" off frequency too far to correct with a trimmer cap is to try. If the trimmer goes all the way to one extreme and the crystal is still off frequency, this is what has happened. Nothing lasts forever.

This radio has an adjustment missing from most 40-channel SSB radios made since 1980 or so. The 10.240 MHz crystal also has a trimmer cap CT201.

73

 

[Lkaskel]

The radio has a separate trimmer cap for each sideband on the carrier-oscillator circuit. One crystal 10.695 MHz crystal X1, two trimmers CT1 and CT2.

The PLL has a 10.0525 crystal that also has the same two trimmers, one for USB, one for LSB.

I'd have to dig out Sams CB series volume 234 to get more specific than that, but those four adjustments almost never remain perfectly stable for 40 years. Only way to tell if a crystal has "aged" off frequency too far to correct with a trimmer cap is to try. If the trimmer goes all the way to one extreme and the crystal is still off frequency, this is what has happened. Nothing lasts forever.

This radio has an adjustment missing from most 40-channel SSB radios made since 1980 or so. The 10.240 MHz crystal also has a trimmer cap CT201.

73

I am looking at the schematic and it appears that CT1 and CT2 are working with the X1 crystal as you have stated. Thinking through this logically (which does not always play out), if I can adjust CT1 to get the proper adjustment for AM/USB then I would think that the crystal is ok. Is that bad logic? I am thinking that CT2 or C2 (which is paralleled to CT2 may be out of tolerance. After looking at the schematic can anyone tell me if I am seeing the possibility correctly?


Thanks as always!!!