Texas Star DX 667V Max PEP Drive Power

[AK #5]

I just bought a mint condition DX 667V with 1 2SC2290 driving 4 2SC2879 Toshibas. The big question is, what is the max amount of PEP I can drive it with? I have gotten 50 different answers on this question, ranging from "no more than 30W PEP" to "PEP doesn't matter, long as dead key is 1-2W".

It is a very nice amp, and I want it to last, because those Toshibas are very expensive, when you can find them, so it would be nice to get a solid, no nonsense answer on this, and put the rumors and hearsay to rest.

Thanks!

 

[TM86]

If I'm reading the datasheet correctly: https://www.rfparts.com/old_site/pdf_docs/2SC/2SC2290.pdf

Then max power input is 4 Watts PEP. Of course, that's measured with a two tone test. Voice that exceeds 4W from time probably won't kill the transistor.

Probably.

 

[999]

I just bought a mint condition DX 667V with 1 2SC2290 driving 4 2SC2879 Toshibas. The big question is, what is the max amount of PEP I can drive it with? I have gotten 50 different answers on this question, ranging from "no more than 30W PEP" to "PEP doesn't matter, long as dead key is 1-2W".

It is a very nice amp, and I want it to last, because those Toshibas are very expensive, when you can find them, so it would be nice to get a solid, no nonsense answer on this, and put the rumors and hearsay to rest.

Thanks!

Here's what I'm gonna tell you, and your mileage may vary.

I have owned my 667V (TWO THIRDS KILOWATT) since 1996... almost 30 years. I have driven it with primarily export radios with either dual finals (bi-polar and mosfet) or an MRF477 for the final. I don't think I've swung more than 35 watts into it even with the radios capable of more than that. I keep my dead key into the amp making ¼ of the total swing on the output. In other words I make sure the amp keys ¼ of it's total swing. I don't give a crap what the radio is dead keying, I make sure the amp is happy. I'm usually sitting somewhere between ½ and ¾ of a watt out of the radio and swing up from there. I have also always had a fan on the amp and I have never blown it up. I have never had a bad audio report running like this, and as a matter of fact I usually get complements on my setup.
Disregard the "2 watt" group and set it up like I have and you'll be running it the same way in 30 years like I am.

 

[9C1Driver]

The 667 can be a cranky beast when overdriven, and it will run hot. Best two upgrades are larger feed wire and add a fan. Don't be surprised if the right AM input dead key ends up being 1 watt or less.
For the PEP input on SSB you can use the law of diminishing returns. If say 22 watts PEP gives you 525 watts out and 30 watts only shows say 550 you know your there. Is the extra drive worth a handful of watts? Probably not.

 

[999]

Best two upgrades are larger feed wire and add a fan.

I forgot to add that I have 4Ga wire on mine as well. That was probably the best upgrade that I have done to the amp. It had the fan on it when I got it.

 

[AK #5]

It has the power wire upgrade done, and a dual fan kit is on it's way for it. My problem, is that my radios do more or less than 30-35W PEP.

My DX88HL keys 1W on AM, but swings past 40W on low, so that's too much PEP for the amp. On SSB, it's right around 30-35W.

It sure is pretty to look at, though...I'll just have to get inside the radio and turn it down, I guess.

 

[AK #5]

Disregard the "2 watt" group and set it up like I have and you'll be running it the same way in 30 years like I am.

Probably not, since I would be pushing 91 years old, 30 years from now...

 

[Onelasttime]

You want a 1 to 1.5 watt dead key in a bipolar powered CB radio and just let the radio swing with out anything like super swing or NPC. That is with a single final radio. So think Cobra bipolar not mosfet finaled 25, 29, 148 etc.......If you can not live with that you need to bypass the driver section and not put in more than 4-11 watts per 2SC2879 transistors what ever wattage get's satuartion of the 2SC2879's.

Do not volt the Toshiba's no matter what any idiots might tell you since those transistors are worth probably $220 each the power from over volting them is not worth it!

 

[nomadradio]

The original DX667 needed a single-final radio with no more than about 16 Watts PEP. Consider that the RCI-made amplified base stations barely swing 14 with the built-in amp turned off. Gotta figure a single 2290 only needs half that. The 667's designers knew this and the radio drive is dropped down with resistors in the input circuit. Later versions cut the radio's drive down more and eventually that model grew the "V" suffix with a drive knob on the front. Problem was, if your radio was big enough to require turning down the drive knob, it had enough power to burn out the "power" pot behind the knob. When dual-final radios became the OTR driver's typical choice, we started bypassing the driver transistor. The driver transistor got the power unhooked and its input coax moved directly to the splitter toroid.

Makes it the equivalent of a DX500. Driving the power from a dual-final radio into a single 2SC2290 just didn't work well.

73

 

[AK #5]

You want a 1 to 1.5 watt dead key in a bipolar powered CB radio and just let the radio swing with out anything like super swing or NPC. That is with a single final radio. So think Cobra bipolar not mosfet finaled 25, 29, 148 etc.......If you can not live with that you need to bypass the driver section and not put in more than 4-11 watts per 2SC2879 transistors what ever wattage get's satuartion of the 2SC2879's.

Do not volt the Toshiba's no matter what any idiots might tell you since those transistors are worth probably $220 each the power from over volting them is not worth it!

I want to use my new Superstar SS88HL to drive the amp. Only problem, is that it's dead key is set at 1W but putting out over 45W PEP, which is too much, and it has a MOSFET final. I'll have to open it up and turn it down.

 

[AK #5]

Problem was, if your radio was big enough to require turning down the drive knob, it had enough power to burn out the "power" pot behind the knob.

73

Is it possible to replace the pot with one that can handle the power?

I really don't want to disable the driver.

 

[AK #5]

Do not volt the Toshiba's no matter what any idiots might tell you since those transistors are worth probably $220 each the power from over volting them is not worth it!

So...13.8V max? I have plenty of those Toshibas, but don't really want to use them by having to replace cooked transistors.

 

[AudioShockwav]

So...13.8V max? I have plenty of those Toshibas, but don't really want to use them by having to replace cooked transistors.

I would suggest you keep it below 14.5 volts most vehicles charge in that range when started.
The bias is fixed, so increased supply voltage means more bias voltage this in turn means you get more heat.
You get a few more watts but it's nothing that will matter on the other end of a QSO and just adds stress to the amp as a unit.
2879 in themselves are extremely rugged but in this design the driver will see more bias and more gain, the finals will do the same and everything supporting them will not take much of that and something will give.
Honestly I don't ask more than 380/400 from 4 2879's anymore, they seem happy there , tolerate a little more reflect,run a little cooler.
Have you tried reducing the AMC setting to see how that effects peak power?

73
Jeff

 

[AK #5]

I would suggest you keep it below 14.5 volts most vehicles charge in that range when started.
The bias is fixed, so increased supply voltage means more bias voltage this in turn means you get more heat.
You get a few more watts but it's nothing that will matter on the other end of a QSO and just adds stress to the amp as a unit.
2879 in themselves are extremely rugged but in this design the driver will see more bias and more gain, the finals will do the same and everything supporting them will not take much of that and something will give.
Honestly I don't ask more than 380/400 from 4 2879's anymore, they seem happy there , tolerate a little more reflect, run a little cooler.
Have you tried reducing the AMC setting to see how that effects peak power?

73
Jeff

The AM carrier setting? Not yet.
My power supply puts out 14.5V so I'm good there. My other one is at 13.9V.
The amp sits atop a nice dual fan kit so no heat related issues.
I just need a radio set up with the proper drive to run it.

 

[AudioShockwav]

Not the AM carrier, AMC is automatic modulation control, a VR on the board that limits peak modulation.
Try this, put the radio on a wattmeter and slowly reduce the microphone gain while talking and note the result on pep.


73
Jeff