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High quality knock of Toshiba 2sc2879?
- Thread starter Enterprise312ok
- Start date
Like the computer-gaming overclockers using liquid nitrogen on their GPUs to get insane frame rates?
73
Seriously considering having Jim @ 307 Amps build me an 8 pill using the 2SC3240s.
Shoukd be interesting.
I have a BUNCH of Toshibas I bought in the early 90s, as I was considering building a bunch of amplifiers to sell, but it never materialized. I also have a lot of brand new unopened gear I purchased back then.
I'm not ready to let them go as of yet.
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I think the biggest reason these 2SC3240 transistors have not seen widespread use in the amplifier market, has to do with its 0.4 ohm input impedance. This is 3.6 times lower than the 2SC2879 and a big enough difference to make the part perform very poorly in a 2SC2879 circuit. This transistor needs more wraps on its input Transformer. Another nice feature is the flange of the Mitsubishi transistor is directly connected to its emitter terminal. This provides a nice low inductance path to ground and improves current distribution to the transistor.
Really, how much work is involved in putting a few more wraps on the input transformer anyway?
The difficult part is understanding why when you place the Mitsubishi part in a Toshiba circuit, it produces less than half of the output. If the person doesn't know the input match is off by more than 3 to 1, they may never overcome this problem.
A SWR meter and coax jumper placed between the radio and the amplifier's 'radio' socket will reveal a lot in this department. Too few turns on the input transformer will show a high SWR between the radio and the amplifier's input.
Some simple SWR meters will reveal whether your SWR is above 50 ohms or below it by comparing the calibrate side of the meter. First set the meter's 'cal' knob into a proper 50 ohm dummy load. Now put it in line with the amplifier. The Cal side will now read higher or lower than it did into a proper 1 to 1 on the dummy. I don't know enough about wattmeter design to tell you which kind of meter reads higher into a load below 50, or lower. Not so tough to find out if you have a handy 25 ohm and 100 ohm resistive load handy. Set the knob to the cal mark on the 50 ohm dummy, then substitute each of those one at a time. You'll see that the needle reads higher or lower on the mismatched loads.
Shameless plug: I sell mismatch loads on fleabay. A set of four includes 25, 50, 100 and 150 ohms. You can make your own a lot cheaper than my inflated fleabay price. Some folks are willing to pay for convenience.
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Some simple SWR meters will reveal whether your SWR is above 50 ohms or below it by comparing the calibrate side of the meter. First set the meter's 'cal' knob into a proper 50 ohm dummy load. Now put it in line with the amplifier. The Cal side will now read higher or lower than it did into a proper 1 to 1 on the dummy. I don't know enough about wattmeter design to tell you which kind of meter reads higher into a load below 50, or lower. Not so tough to find out if you have a handy 25 ohm and 100 ohm resistive load handy. Set the knob to the cal mark on the 50 ohm dummy, then substitute each of those one at a time. You'll see that the needle reads higher or lower on the mismatched loads.
Shameless plug: I sell mismatch loads on fleabay. A set of four includes 25, 50, 100 and 150 ohms. You can make your own a lot cheaper than my inflated fleabay price. Some folks are willing to pay for convenience.
73
If your calibrate side reads lower than it did into the 50 ohm dummy load, the antenna impedance (or input to the amplifier) is below 50 ohms. If the calibrate side reads higher than it did into the 50 ohm dummy load, the load impedance is above 50 ohms. It's all about RF voltage and you get a higher voltage drop, across a higher impedance load.
This is a very good tip by Nomad. Because, it identifies the problem and which direction you need to go in order to correct it, with minimal test equipment required.
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I'll have to look and see if I can find Helge's Motorola pub on broadband transformers.
If you can't find it there it doesn't exist, doesn't matter or can found at communications concepts, or Freescale/NXP.
While I'm at it I saw reference to "just add more turns on the primary winding of the input transformer" .
Unlike Andy or Nomad I'm not going to write a book on the subject because Dye and Granberg already did. The devilish bit is the circuit is restricted to "quanta" , as in number of turns. You may need a 1/2 or 1/4 turn, then what?
Over simplifying the fix, it takes capacitance across the Low Impedance side of the transformer to balance out the additional inductance.
Except when it doesn't.
All the math is there. Just believe the results.
While I'm at it I saw reference to "just add more turns on the primary winding of the input transformer" .
Unlike Andy or Nomad I'm not going to write a book on the subject because Dye and Granberg already did. The devilish bit is the circuit is restricted to "quanta" , as in number of turns. You may need a 1/2 or 1/4 turn, then what?
Over simplifying the fix, it takes capacitance across the Low Impedance side of the transformer to balance out the additional inductance.
Except when it doesn't.
All the math is there. Just believe the results.
LA 900 moble amp.
Anyone know who makes this amp? I been looking for a sch-matic or drawing of the inside......Thanks for any help.
One of the the best ways to un-confuse an impedance match in a broadband transformer is to get the DC off it. Find any reference to Steve Canfield here and you'll see the Fairly rare (no one else did it), Insightful use of a bit of extra ferrite in his designs. After seeing this I wondered to this day why Steve was the only (well, nearly) builder to do this.
I know where Steve is (was?) but he's made it clear that he's done with this and didn't bother him further. I did get a reasonable welcome but he has no interest.
Amen.
1-800 Toll Free would smile at that statement....
" give that man a cigar"
73
Jeff