galaxy saturn am only problem

[brent stroud]

hello I've got a problem that has me scratching my head. I have a saturn than has normal dead key on am but only swings 6 to 8 watts on am. I have 6vdc on the final collectors in am mode and normal output power of 20 plus watts on ssb. 12.5vdc in ssb mode. anyone have any ideas on this ?

 

[nomadradio]

I have seen a lot of Saturns that had the bias turned way too high on the finals. Makes them run hot, and turns the metal tab black. As a rule, one final will croak first, cutting the power more or less in half. A flat-black layer of oxide on the metal-tab surface of a final transistor is a bad sign.

There is one capacitor between the final collector choke coil and the slug-tuned output coil. Older radios used a ceramic disc cap that would get hot and go bad. Some time in the early 90s they changed this to a silver-mica type. Can't remember the callout number on the schemo, but those are the two failures that come to mind.

Of course, you did align the transmitter stages upstream from the final, right? Just one tuning slug that's not peaked can do this as well.

73

 

[brent stroud]

Yes I sure did. The bias is right where it needs to be. What’s really strange is the fact that ssb mode works fine with normal power output but I will double check what you just suggested thank you Chris

 

[brent stroud]

I have seen a lot of Saturns that had the bias turned way too high on the finals. Makes them run hot, and turns the metal tab black. As a rule, one final will croak first, cutting the power more or less in half. A flat-black layer of oxide on the metal-tab surface of a final transistor is a bad sign.

There is one capacitor between the final collector choke coil and the slug-tuned output coil. Older radios used a ceramic disc cap that would get hot and go bad. Some time in the early 90s they changed this to a silver-mica type. Can't remember the callout number on the schemo, but those are the two failures that come to mind.

Of course, you did align the transmitter stages upstream from the final, right? Just one tuning slug that's not peaked can do this as well.

73

Yes I sure did. The bias is right where it needs to be. What’s really strange is the fact that ssb mode works fine with normal power output but I will double check what you just suggested thank you Chris

follow up. I traced modulated audio from ic 4 all the way thru tr 49 50 and 51. all the way to the collectors of tx finals. has tx audio. I'm totally stumped. once again. ssb tx is normal. just no forward pep on am.

 

[bob85]

Brent,
what meter are you measuring the AM swing with

if its an average reading meter you will see swing on ssb but not much swing on AM unless its setup to swing from a low carrier,

6V on the collectors sounds like factory carrier level on AM for export radios

 

[brent stroud]

Brent,
what meter are you measuring the AM swing with

if its an average reading meter you will see swing on ssb but not much swing on AM unless its setup to swing from a low carrier,

6V on the collectors sounds like factory carrier level on AM for export radios

I'm using a pep reading watt meter. for sure. thanks for the suggestion though.

 

[brent stroud]

UPDATE: problem solved bad cap in audio circuit on output of 4558 op amp. Thanks for the suggestions guys.

 

[Blitz]

UPDATE: problem solved bad cap in audio circuit on output of 4558 op amp. Thanks for the suggestions guys.

Was it just low power or low audio on AM also?

 

[brent stroud]

Was it just low power or low audio on AM also?

low audio on am mode only

 

[Blitz]

low audio on am mode only

Thanks for getting back to me, thats exactly my problem, do you remember which cap it was.