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Author Topic: Transistor specs at different frequencies  (Read 1265 times)
KM1H
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« Reply #15 on: January 12, 2018, 03:41:01 PM »

Many if not most 100-200W 160-10M discrete transistor rigs make less power on 10m be they 12V bipolar or 28V FET; yet they are rated as 2-30 mhz.

Carl

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G3RZP
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« Reply #16 on: January 13, 2018, 08:43:35 AM »

Quote
Many if not most 100-200W 160-10M discrete transistor rigs make less power on 10m be they 12V bipolar or 28V FET; yet they are rated as 2-30 mhz

Very true, Carl, but is this caused by the active device or the matching transformers or other parts of the PA circuit?
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KD0REQ
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« Reply #17 on: January 13, 2018, 09:55:01 AM »

well, in hollow-state days, the negative feedback to prevent parasitics had a lot to do with it.

on semis, if you get a spec that shows effective gain against frequency (most often in op amps,) you will see either a straight line down, or a flat line to some frequency and then a downward slant. not being a semiconductor applications engineer, and barely able to spell it, on a discrete device this would probably be due to internal factors like interdie capacitance and skin effect across the junctions running into less and less skin to effect. probably compensation issues in a complex circuit like a packaged op amp. I don't think you'd see anything like quantum leakage at any ham frequency in common use.

if ZRP, being one of those engineers, doesn't have the answer at hand, it's a cosmic dark secret.

// afterthought // our comp sci class in the early 80s had a lecturer from Univac, who specialized in failure analysis, show us photomicrographs of failed semis, where they dissolved the epoxy off with methylene chloride. he said sustained overdissipation (too dang hot for too dang long) would melt the junctions, where peak use failure (100 watts from a 10 watt device spikes) would go open. so if the "typical" graph shows 10 watts, and this means some devices will not hit 10 and some might provide more for a short time, don't plan on goosing the device past recommendations.
« Last Edit: January 13, 2018, 10:17:14 AM by KD0REQ » Logged
KM1H
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« Reply #18 on: January 13, 2018, 02:03:39 PM »

Quote
Very true, Carl, but is this caused by the active device or the matching transformers or other parts of the PA circuit?

Good question Peter that I dont have an answer to.

OTOH the rigs Ive tested using an amp module do not appear to have that problem and are equal power to 6M. Granted that is a small sample and includes SDR.

Carl
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