power output question about the sd1446

[222DBFL]

I think the problem lies in too much input power from the radio, not on key up, but the swing wattage that is produced is over driving the amp. I would try a single final radio if possible and see what happens or get an amp that has the 2879 toshiba transistors in it for use with a 2950. Have you looked at your board to see if it is possible to put the larger transistors in it, I know the ones I have seen have the larger holes already stamped out. Just seems like a classic case of over driving the amp is the issue, not your meter or VSWR, from all posts I have read thus far. I could be way off base here but this is what is all apparent to me anyway. If your 2950 is like the ones I have owned in the past, they are best suited for use with a high drive amp. Good luck and hope you get it sorted out. God bless.

 

[Shockwave]

I think the problem lies in too much input power from the radio, not on key up, but the swing wattage that is produced is over driving the amp. I would try a single final radio if possible and see what happens or get an amp that has the 2879 toshiba transistors in it for use with a 2950. Have you looked at your board to see if it is possible to put the larger transistors in it, I know the ones I have seen have the larger holes already stamped out. Just seems like a classic case of over driving the amp is the issue, not your meter or VSWR, from all posts I have read thus far. I could be way off base here but this is what is all apparent to me anyway. If your 2950 is like the ones I have owned in the past, they are best suited for use with a high drive amp. Good luck and hope you get it sorted out. God bless.

Except the problem is most pronounced and seen in the high VSWR when the drive is at its lowest 2 watt carrier level. It gets better as drive is increased. Although, I will point out that the old 2950 chassis has been known to oscillate under some conditions. If that is happening this will pass right on to the next stage and present the same symptoms.

 

[Robb]

Except the problem is most pronounced and seen in the high VSWR when the drive is at its lowest 2 watt carrier level. It gets better as drive is increased. Although, I will point out that the old 2950 chassis has been known to oscillate under some conditions. If that is happening this will pass right on to the next stage and present the same symptoms.

To test that possibility, he would need to try another radio - preferably bone stock - and see it it was the amp or the radio that caused the amp to oscillate?

Didn't say anything about the biasing of this amp - BTW.

 

[Shockwave]

He could just go to SSB with the mic gain turned down to drive the amp below 2 watts. I didn't mention the bias because I don't have enough info about the particular amp. Palamar is also not noted for having bias problems related to oscillations like Texas Star for example.

 

[222DBFL]

I think there is a problem at the radio as well, but could be wrong, I asked earlier if it was possible to switch out radios but never heard back from poster, I am curious about his one.

 

[cjruger]

Ok, just caught up reading here

Im fairly certain the meter( workman) is ok at least at the lower wattage. The 2950 dead keys at 2 watts and thats what the guy i bought it from told me it did. Second i picked up a stock cobra 29, shows it keying at 4 watts right on

I do think there could be a cap missing in the amp, when i got it there was one floating around in there. It was burned up and i could not find where it came from. I wrote it off as being left in from a assembly error. I am capable of putting one in but have no idea how to figure out where it goes

 

[222DBFL]

Get the dead key suppressed to at least 2 watts and a good peak and tune and alignment and see what the cobra 29 will do, the cobra 29 is a relatively easy radio to work on and can be made to run an amp like you have quite well!! Good luck and hope you get it sorted out.

 

[Robb]

Ok, just caught up reading here

Im fairly certain the meter( workman) is ok at least at the lower wattage. The 2950 dead keys at 2 watts and thats what the guy i bought it from told me it did. Second i picked up a stock cobra 29, shows it keying at 4 watts right on

I do think there could be a cap missing in the amp, when i got it there was one floating around in there. It was burned up and i could not find where it came from. I wrote it off as being left in from a assembly error. I am capable of putting one in but have no idea how to figure out where it goes

Could well be a game-changer!

Was not an assembly error.
Who would just toss back in a burned up cap?
Very unlikely!

 

[222DBFL]

Could very well be, you say you can't find where it goes, maybe an photo of the board would help someone in your quest to get on the right path. Again hope you get it figured out, you have peaked my interest for sure.

 

[Crusher]

Shockwave is on the right track. With meter ruled out, its in the amp. I think I read on the first page he was using a 2950? If so, I have seen many "export radios" that did all sorts of strange things when put into a small transistor amp. Maybe its the lack of a properly tuned radio causing. Even so far as the amp to squeel until unkeyed. I have seen this happen more times than I can count. But yes I agree negative feedback, or some kind of additional padding/ swamping of the input may help. Just my 2 cents.

 

[222DBFL]

The Motorola transistors aren't as stout as the good old 2879 toshiba transistors. Makes a difference as far as what radio should be used, the 2950 is a dual final radio with some power and I think the amp isn't liking it, hopefully he gets it figured out before the transistors take a poop.

 

[cjruger]

Could very well be, you say you can't find where it goes, maybe an photo of the board would help someone in your quest to get on the right path. Again hope you get it figured out, you have peaked my interest for sure.

Here ( i think from memory and may have been a cap, cant remember ) is what was floating around, not sure what it is. Followed by pics of board. And i do see 4 holes where its possible it was. They are in the second pic.

 

[222DBFL]

Wait until the morning and I will have a peek under the hood of mine, maybe I can see what you are missing here.

 

[Crusher]

So it is biased and class C at best.

 

[cjruger]

Wait until the morning and I will have a peek under the hood of mine, maybe I can see what you are missing here.

Thanks, that would be great. Here is a little better pic