Texas Star DX350 - SSB delay causing loss in power output

[linearone]

Just clip the resistor

 

[Tucker442]

It appears I can jump pins 2&3 to get full power w/ ssb delay active. Will be trying that. Thanks for the help.

I’m sure it has a lot to do with input also. I don’t think 25 W on sideband would hurt this amp at all.. A.m. that’s a different story.

 

[CbRadiosPRONTO]

Be sure and listen to it on another radio before and after.

The designer combined those two functions on the SSB button because sideband doesn't tolerate overdriving the transistors as well as AM mode does.

If you're okay with how it sounds, that's the opinion that matters, right? The drive gets reduced by that button to reduce flattopping. The peaks of your SSB RF envelope get clipped with full drive. The resistor reduces this effect by reducing drive level.

And a glance at this with a 'scope would confirm my suspicion, that peaks are getting flattened with the a jumper on that resistor.

73

Thanks for that. We will see what happens with various input level and a two-tone signal. I figured there had to be something to that. It doesn’t make any sense, whatsoever, to make the switch a “dual-purpose” switch unless they have good reason.

 

[AudioShockwav]

I think TS must have made that change when they stuck that little rocker switch on the back for SSB.
It looks like now it just turns on the delay.
The older ones did not work that way.
They have made changes before that just appear and you don't know untill the lid is pulled.
I could not believe it when I opened a 667 and found 2 mosfets for a 2290, That was a eye opener

73
Jeff

 

[CbRadiosPRONTO]

I think TS must have made that change when they stuck that little rocker switch on the back for SSB.
It looks like now it just turns on the delay.
The older ones did not work that way.
They have made changes before that just appear and you don't know untill the lid is pulled.
I could not believe it when I opened a 667 and found 2 mosfets for a 2290, That was a eye opener

73
Jeff

Lol yeah. Gosh that dual mosfet thing was like a dozen years ago ‍

 

[nomadradio]

Forgot all about the rocker-switch SSB select.

My discussion only applies to the pushbutton "SSB" on the front panel.

One drawback of being an old goat. Remembering only the old way of doing something.

73

 

[CbRadiosPRONTO]

Be sure and listen to it on another radio before and after.

The designer combined those two functions on the SSB button because sideband doesn't tolerate overdriving the transistors as well as AM mode does.

If you're okay with how it sounds, that's the opinion that matters, right? The drive gets reduced by that button to reduce flattopping. The peaks of your SSB RF envelope get clipped with full drive. The resistor reduces this effect by reducing drive level.

And a glance at this with a 'scope would confirm my suspicion, that peaks are getting flattened with the a jumper on that resistor.

73

Am signal didn’t look too bad when the AM (attenuation) button was pressed. Only 3w carrier and 9w pep input. Slightly under modulated. I’d recommend 2.5w carrier and 10w pep. Very efficient amp.

The original post questioned why the ssb dropped the rf power. As mentioned by several, the ssb button creates a delay AND attenuates the signal. NOMAD is right about the reason for that design; as you can see by these photos (which I hope post in order).

The original ssb signal (radio only) looked terrible. I tuned it a bit and it looked just ok at 25w pep ssb. That’s where I took the first measurements driving the amp. Not great results but they’re
even worse when amp is on high. Then I re-tuned the radio and dropped the power from the radio to 9w ssb just to make sure I was starting w/, what I thought, was a nice looking ssb signal on the scope. The results were defiantly better but meh, you decide.

Note: This amp is old. I really don’t know it’s history. Maybe a new one would look great on a scope. This isn’t that scientific but it was interesting.