Texas Star 350 variable pot & drive question

[KK4JW]

From what I seem to remember, the TS potentiometers were a weak-link with these amplifiers. Is there an upgrade part out there that would be better suited?

As the potentiometer is merely a variable resistor, is there anything stopping me from checking the resistance of the pot once "set" and then bypassing /replacing it with a fixed resistor of the same value and never worrying about it again?

I've also read to just turn the knob wide open and let er' eat, and control everything with the radio's input to the amp. I'd really prefer to do this as it would simplify things, but I'm afraid of burning out the pot as I've heard rumors of.

That brings to mind another question, regarding the 350. Is it true that the 350 and 350HDV share basically no difference other than the faceplate and buttons? I've read (and want to dispel) that the internals are identical and the "HDV" is just a marketing gimmick.

The model I have is technically a 350HD with the dial a watt knob (2x2879's). What would be a good, solid drive/PEP for this amplifier to keep it happy? I want to drive it good, to get good outpout out of it, but I don't want to push it too hard and create excessive heat/stress just for the sake of a few watts that no one will ever see. I plan on setting it, forgetting it, and enjoying it.

 

[999]

From what I seem to remember, the TS potentiometers were a weak-link with these amplifiers. Is there an upgrade part out there that would be better suited?

As the potentiometer is merely a variable resistor, is there anything stopping me from checking the resistance of the pot once "set" and then bypassing /replacing it with a fixed resistor of the same value and never worrying about it again?

I've also read to just turn the knob wide open and let er' eat, and control everything with the radio's input to the amp. I'd really prefer to do this as it would simplify things, but I'm afraid of burning out the pot as I've heard rumors of.

That brings to mind another question, regarding the 350. Is it true that the 350 and 350HDV share basically no difference other than the faceplate and buttons? I've read (and want to dispel) that the internals are identical and the "HDV" is just a marketing gimmick.

The model I have is technically a 350HD with the dial a watt knob (2x2879's). What would be a good, solid drive/PEP for this amplifier to keep it happy? I want to drive it good, to get good outpout out of it, but I don't want to push it too hard and create excessive heat/stress just for the sake of a few watts that no one will ever see. I plan on setting it, forgetting it, and enjoying it.

I'm going to post pictures of the layouts for you.

DX350

DX350HDV

There are a couple of minor differences in the layout, but the overall circuits are the same.
The std amp have 4 power levels and the SSB delay is attached to the front button along with one of the levels.
The HDV amp has 2 fixed levels with the variable and the SSB delay is stand alone on a rocker switch on the rear of the amp. This allows the delay to be active at higher power outputs than the std amp.
The amplification circuits are the same between the amps, only the control is slightly different.

So yes, the potentiometers are the weak link and I wouldn't run them for any length of time anywhere but in the fully open position. If you find a higher rated potentiometer you can replace the stock one, but I don't really know what's available to do that. I wouldn't install a set value resister in place of it because then you are limiting the output potential for no good reason. These should be able to run wide open for many years with no issues.
If you are trying to run a high output radio into it, I would choose either a different radio, or different amp to run it into.

My $0.02

 

[KK4JW]

I'm going to post pictures of the layouts for you.

DX350
View attachment 64789

DX350HDV
View attachment 64790

There are a couple of minor differences in the layout, but the overall circuits are the same.
The std amp have 4 power levels and the SSB delay is attached to the front button along with one of the levels.
The HDV amp has 2 fixed levels with the variable and the SSB delay is stand alone on a rocker switch on the rear of the amp. This allows the delay to be active at higher power outputs than the std amp.
The amplification circuits are the same between the amps, only the control is slightly different.

So yes, the potentiometers are the weak link and I wouldn't run them for any length of time anywhere but in the fully open position. If you find a higher rated potentiometer you can replace the stock one, but I don't really know what's available to do that. I wouldn't install a set value resister in place of it because then you are limiting the output potential for no good reason. These should be able to run wide open for many years with no issues.
If you are trying to run a high output radio into it, I would choose either a different radio, or different amp to run it into.

My $0.02

Wow, thank you so much for all of this. I appreciate it.

I *was* planning to turn down my Stryker 447 to run into it, but decided against that. I'm just going to hit it with a dual mosfet Connex radio that peaks about 45 clean watts.

Thank you again for your information and advice. I'll just turn the knob wide open and leave it there.

Edit: Hypothetically, let's say the knob/pot decides it doesn't want to be a team player anymore. Do I HAVE to replace it? Is there a way it can be bypassed? I mean, if it's going to be left wide open all the time anyway?

 

[Greg T]

Wow, thank you so much for all of this. I appreciate it.

I *was* planning to turn down my Stryker 447 to run into it, but decided against that. I'm just going to hit it with a dual mosfet Connex radio that peaks about 45 clean watts.

Thank you again for your information and advice. I'll just turn the knob wide open and leave it there.

Edit: Hypothetically, let's say the knob/pot decides it doesn't want to be a team player anymore. Do I HAVE to replace it? Is there a way it can be bypassed? I mean, if it's going to be left wide open all the time anyway?

Turning down the stryker is easy. You have the ability to tweak the high power as well as the low power independently. That thing can be setup to power any amp and still have full power output.

 

[9C1Driver]

45 watts peak into a Texas Star 350 is really pushing it. Not sure where you have the input carrier set at. Whatever input dead key that gives you a 60-80 watt dead key output from the amplifier will work good. It will probably be 1.5-2.5 watts.

Most cb type amplifiers are really low drive amps. They know if they stamp HD or High Drive on them they sell better. As an example years ago a local was running a Galaxy 88 (hi Lo) with a TS350 HDV. On low the the radio keyed 2 watts and 8 watts on Hi. He sounded superb on the Lo setting. He then announced he was really going to kick some butt and put the radio on Hi. He now sounded all pinched up and garbled. His response was, "but it's a Hiii Driiive amp".

 

[Shadetree Mechanic]

I used to run a 350 HDV with my President Madison. The modulation would make the ferrites rattle. Now I run a 500v, runs clean and cool.

 

[linearone]

I find variables in cb amps only useful in a very specific set of circumstances. When driving one amp into another , sometimes, due to a pile of reasons , you may want to limit the over all output of a stage by limiting the overall input to that stage. It doesn't really control your carrier, your radio does that. It also doesn't control your carrier to modulation peak ratios, your radio does that.
I also find transistor amplifiers are far more prone to hangups with overdrive than tubes are. They can get crunchy quick. You give a 500z 80w or 200w..it kinda doesn't matter. Sure things get spectrally trashy but they still sound ok.
Transistors when even slightly overdriven immediately get tight sounding.

I barely need variables. I use my radio to do that.

 

[linearone]

I used to run a 350 HDV with my President Madison. The modulation would make the ferrites rattle. Now I run a 500v, runs clean and cool.

Some folks would put a squirt of Silastic or something across the valley of the cores to keep them quieter. I used 5 min epoxy on a few.