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Toshiba 2290 max input questions

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KangMudDuck

Member
Mar 5, 2021
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Hello
I picked up a Texas Star Skeleton 150 from a local guy with two Toshiba 2290s. Spec sheet on the 2290 says max input 4 watt PEP. I put the amp on the bench, 13.8 volts, running a Cobra 148 with 12 watt PEP. Meter is showing 250 watt PEP. Am I asking for trouble with this set up?

I watch this video and wonder if the 2290's specs are way undervalued for power input, he is putting 35 watts PEP into it and getting 300 watts out with 15 volts. I don't have the ssb delay on the amp I picked up.
 

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I think 2SC2290s are rated at 60W RMS so 240-250 isn't unheard of.

I've seen videos of 2 pill 2290's doing 300 but probably not very clean at that point.
 
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You can run any sort of combination of input caps and resistors to run the amp UP to an output.

Didn't say CLEAN output...

Review the Vid, you'll see other work done to it to make it do that 220 watt figure - of merit - SIC

Skeleton - being what it is, means no board and it's mostly point to point.

upload_2021-5-11_18-0-18.png

You can find all the stuff you needed to know at:
http://www.cbtricks.com/Amp/txstar/index.htm
 
@Handy Andy Thanks for your reply. I have read quite a bit here at this forum from you and others, however I find myself lost very quickly. My understanding of electronics is very limited, I barely remember a section on circuits in a physics class 30 years ago. I am trying to learn by reading through a book "Secrets of RF Circuit Design" by Joseph Carr, reading forum posts and watching youtube videos.

Without having an advanced degree in electrical engineering and without the luxury of spending many hours of fiddling with different combinations of transformers, resistors, capacitors, relay switches etc, how can a person get a better grip on this? Is there a formula or equation to go by to select the correct values for capacitors and resistors so the Skeleton 150 would sound good with a higher drive? Is there an amplifier school techs go to, how does one learn this?

I am using a Lincoln II in my car now, I am very impressed with its sideband operation, I routinely make DX contacts. I'd like some more oomph on the AM side and thought the Skeleton 150 would be a good addition, low amp draw and compact for the car. I am scared to death of putting 18 watts from the Lincoln into the amp and frying the transistors. How would I go about matching the radio to this amp?

Attached is a photo of a Palomar 350 HD I pulled out of a storage box, used to use this amp with the same Cobra 148 25 years ago. This amp sounded clean back in the day, but it sucked a lot of amps out of my car back then, to the point the car would shudder if I tried to drive and key up. Usually used the amp while parked in the driveway with a charger hooked up to the battery. When I hooked this box up to the meter running the same Cobra 148 used with the Skeleton 150, I'm getting about 220 watts PEP. It also buries the needle on the amperage meter on the 30 amp power supply I am using.

The data sheet for 2789 says the max input is 10 watts, so putting 18 watts from the Lincoln shouldn't be harming the transistors, I would assume. How would I correct the outrageous amperage draw on the Palomar? What amp would be safer to use with the LIncoln?

(Also, a lot of locals keep saying Lincoln II and AT-6666 have fried finals because people are putting them on amps, they say they saw it on the internet. Outside of bad SWR and reflected watts, how are the finals affected? Wouldn't the transistors be taking the brunt of the damage?)

Thank you very much for your help, I know I am asking a lot.
 

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Hmm...Without having to bring you into the Ph.D. and Admissions office...:)

Yes, to many of your questions...but it will take a long post in which to answer them all...

Remember that this discussion is about; "How many watts can you put into xxxx transistors?"

The truth is, not much as far as actual power input, but you can use the amp, it's the output power the radio has to put into it, is. That's the problem, you just have to fashion a way to Attenuate (reduce) the power of the output of the Radio to do this.

  • you brought up an interesting Amp to try and relate the amp to running the transistor "pair" and how it differs.
  • On thing I tried to point out, are those differences in the values - the circuits are essentially the same to both.
  • So when you mention things like Finals toasting and getting toasted, - Yes, there is some truth to those rumors...
  • It's in driving the amp PROPERLY without killing both in the process...
  • True? Yes, but there are SUBTLE changes in both amps - Caps, Resistor Biasing and even the transistor pair themselves - small changes give you 150 watts, or 220 watts.
  • It's incorporating them into your radio and Amp - unless you want to play Doctor - it's best to get a techy involved... Becasue this will not be an easy surgical outpatient clinic sort of operation.

Here's the problem, these amps run Class C - so they aren't made very well for AM and nearly impossible on SSB at least not without some work.

So this brings you to what you have, a Palomar 350HD - Great little Amp - so, if you want to use it with the Lincoln - hmmm . . . now you just have to "turn down" the Lincoln to run it.

That's part of the problem - the Lincoln is capable of a LOT of drive to hold it's own Unless you have a really big amp, which can utilize the DYNAMIC output the Lincoln has (AM, SSB, FM modes to name a few) the Palomar is really meant, and designed for small 4 watt Cobra 29's or similar platforms - not a lot of power needed to drive the amp - the Lincoln will kill it in just a few minutes.

You can try to "pad with resistance" to tame the dynamics of the Lincoln, but it's not a cure all, nor is turning down the Lincoln innards at the ALC and AMC with Carrier swing limits, for if you try to run it stock without the Boot, you're a Sitting Duck...

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​
So, if you want to run the Lincoln, the Palomar can do it, but limits both in performance, can't run one without the other sort of thing.

You have to make some decisions...

How do you want to proceed?
 
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So, there's a guy here local with 5 2879 toshiba red dots. Due to my ignorance I'll ask this question. I notice they're offered in matched set for amp builds. These are just 5 left over pills from years back, could they be used together for say a 4 pill amp build? He's asking a hun a piece so the price seems nice if they could be used for a build or even a replacement.
 

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