-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
DEI Transistors
- Thread starter Drifter
- Start date
Some useful info here......
https://www.arworld.us/PDFs/appNotes/AppNote49.pdf
and here:
http://faculty.sdmiramar.edu/faculty/sdccd/wnorth/109c/AMT109Cfive.pdf
https://www.arworld.us/PDFs/appNotes/AppNote49.pdf
and here:
http://faculty.sdmiramar.edu/faculty/sdccd/wnorth/109c/AMT109Cfive.pdf
Two meters show the same and the one I use is the Daiwa, which is tighter than my MFJ. In any case, the power wire upgrade made a huge difference.
Here's where ohms law fails me in RF.... If you use Ohm's Law with 14.7VDC and say 65A, it gives you .226 ohms and 955.5 watts.... Where does the 50 ohm load (coax) come into play for the calculation? The entire transmission length has a 50 ohm load yet you cannot figure that into the equation.
Last edited:
The amplifier is converting DC input to RF output. The .226 ohm input resistance is what it takes to draw close to a thousand Watts from the DC line. To produce a similar output power into 50 ohms, means the RF voltage is much higher than the DC voltage. Someplace over 200 volts of RF. With approximately 200 volts of RF applied to a 50-ohm antenna system, we are delivering 800 watts of RF to that antenna.
Fast forward to year 2023... Toshiba 2879's are so rare, builders are ripping them out of perfectly good older amps, especially the beat up Texas Stars you find at fleamarkets and hamfests. They then test them, clean them, test them again and post on eBay for $125 a pop. Meanwhile, other amp builders found the HG's to be plenty good in their builds, especially the HG2sc2879c pills and can stand being volted and driven hard.
Hg pills are plenty good enough for me, Toshibas are a status symbol these days. I got 600 average out of a biased 4 pill 2978c box I was testing. At 19 volts on my regulated linear supply.
This is where I don't understand people. Don't get me wrong, not trashing you at all, but I don't understand why people would pound the hell out of a transistor with 19 volts to get an output that is roughly the same as my Texas Star DX-500 with DEIs in it. I run my DEI-filled 500V at 14.5V and with a 45 pep input I'm getting about 600 to 700 pep out. And everyone tells me audio is loud and squeaky clean.
But, lets say just for S&G that the DX-500 was getting it's namesake in power out. Okay, 500 safe pep watts at 13.8V. Why would anyone pound it up to achieve 600 or even 650 when the outcome will be totally undetected? Nobody on the other end will hear one bit of difference, except for maybe WORSE audio. Signal received will be the same. This never made sense to me.
The Competition players are what made Toshiba the king of rf devices @27 Mhz in the past.
I have ran them at 22 volts, class c before, driving the snot out of them and they lived, I doubt a HG or DEI would have survived that abuse.
They had so much headroom over the data sheet specs it was unbelievable.
73
Jeff
I have ran them at 22 volts, class c before, driving the snot out of them and they lived, I doubt a HG or DEI would have survived that abuse.
They had so much headroom over the data sheet specs it was unbelievable.
73
Jeff
Boy the toshibas were such a fun time, makes me sad the party's over
On the plus side there are still at least 4 worthwhile triode part numbers that make for fun. If you aren't afraid of high voltage.
The comp builds had one single objective, produce the maximum amount of power per device possible.
One individual , who had some experience with 27 Mhz plasma applications ( plasma cutters) also like to play radio found you could press the Toshiba into service volted beyond manufacturing specs and they stood up to the challenge, producing more power than the other guys dreamed of.
He started cutting lips off and winning belts and trophies.
Suddenly every one wanted to have that , and the rest is history.
This part of it had nothing to do with how clean a amp was, how long it lived.
All that mattered was who came out on top of the gate.
73
Jeff
Boy the toshibas were such a fun time, makes me sad the party's over
On the plus side there are still at least 4 worthwhile triode part numbers that make for fun. If you aren't afraid of high voltage.
I don't run much at all mobile now.
If I want to go play mobile I just go park on a mountain and put 4000 feet under my antenna.
It's easier than all that work running a big amp mobile.
I am getting old and a little lazy.
73
Jeff
- No one is chatting at the moment.