Electronics > RF, Microwave, Ham Radio

help on design of a transistor amplifier

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Im trying to modify one old transistored beacon with modern front end and keep the old final amplifier. The problem is like this way........................
 I have an old beacon amplifier with 4 transitstors, 2 in pairs. Max. output by the papers are 100w and pep 400w. Im including you the schematic,
My project is to remove everything from the final driver board and front and keep from T202 and rear, the finals, the output transformer etc.
Now to make some experiments, i made one new T202 made from 32 turns primary and the secondary is 7+7 turns. 32 turns is the original one but with a center tap. I was rewind it without the center tap. Im using one class A amplifier to drive the finals. BUT i get a very distorted signal in oscilloscope. im sending you some screenshots to get an idea, by the way, it is a AM carrier and with CW modulation. It is a beacon for direction finding. and working real low 400-500Khz, and thats the reason for the wattmeter.

here is the original schematic

remove everything from T202 and to the left
next is the driver that i made

sorry, some problems on the attachments,
here is the original schematic, the first is the drivers that i used

you can see the coil that i wound, and that i have a good AM modulated signal on the output of the coil, but when i connect on the final transistors i get this ungly modulated signal, why this???

any help please why i geto so much distorted signal on the output please????

Where exactly are you probing the output signal? Do you have a 100W 50Ω dummy load on the output?

Did you probe the output before you replaced the previous stage? I'm wondering what the reason was for you replacing a push-pull amplifier with a single ended one.

The output looks like it's overmodulated. Are you sure the original preamp was 4W output? You may be overdriving the final PA transistors.

What does the output look like with no modulation?

Paul Price:
You've posted the wrong schematic. Your description of the device doesn't seem to be even close to what the schematic shows.

The circuit  you first posted using a low-freq TIP darlington transistor would likely feed a buoy audible-freq. device loudspeaker/transducer  for a fog horn.


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