Hi smoking-amp,
Fortunately, my old frequency generator have a distorsion problem at the lower frequency's only, above 1khz, it is not so bad. I mesure the frequency response of my 1$ autotransformer and it seem to be very good, there is no loss from 20Hz to 2Khz and just - 0,35dB at 20khz ... Almost perfect !
But I have to mention the test was done with a 100 ohms load resistor and only 10V RMS "high voltage", so it was at about 3 mW ... Maybe, the frequency response will not be as good at 3 or 4 watts ... But I think the coupling factor is very high since it is a autotransformer. Maybe, my simulator have some problems with the autotransformers because I try a standard transformer in another circuit and there was no problems with low coupling factor ???
By the way, I verifiy all the tubes of my frequency generator and I change two I already have in my stock, but I have to find two rare metal 6FS5GA (or a two glass one), miniature 6FS5 exist but I won't modify that venerable instrument to use them instead of the old octal types ...
There is a very precise analog voltmeter on it, absolutely linear from 20Hz to 20Khz, I compare it to my scope and it work perfectly. In the meantime I found the two 6FS5GA, I will build a 2206CP based multifunctions generator, 0,001Hz to 100Khz ... I already made the PCB and solder all the parts on but I don't make the cabinet yet. I will also add some 2SK170BL bipolar buffer amps "output capacitor less" I design to give more power to the sine, triangle and square waves outputs.
So, I still believe my autotransformer can do a good job in my DN2540 / 12C5 project ... If not, I will use a small standard SE output transformer, with no DC in the primary, I will get more power and bass out of it.
Cheers,
Alain.
Fortunately, my old frequency generator have a distorsion problem at the lower frequency's only, above 1khz, it is not so bad. I mesure the frequency response of my 1$ autotransformer and it seem to be very good, there is no loss from 20Hz to 2Khz and just - 0,35dB at 20khz ... Almost perfect !
But I have to mention the test was done with a 100 ohms load resistor and only 10V RMS "high voltage", so it was at about 3 mW ... Maybe, the frequency response will not be as good at 3 or 4 watts ... But I think the coupling factor is very high since it is a autotransformer. Maybe, my simulator have some problems with the autotransformers because I try a standard transformer in another circuit and there was no problems with low coupling factor ???
By the way, I verifiy all the tubes of my frequency generator and I change two I already have in my stock, but I have to find two rare metal 6FS5GA (or a two glass one), miniature 6FS5 exist but I won't modify that venerable instrument to use them instead of the old octal types ...
There is a very precise analog voltmeter on it, absolutely linear from 20Hz to 20Khz, I compare it to my scope and it work perfectly. In the meantime I found the two 6FS5GA, I will build a 2206CP based multifunctions generator, 0,001Hz to 100Khz ... I already made the PCB and solder all the parts on but I don't make the cabinet yet. I will also add some 2SK170BL bipolar buffer amps "output capacitor less" I design to give more power to the sine, triangle and square waves outputs.
So, I still believe my autotransformer can do a good job in my DN2540 / 12C5 project ... If not, I will use a small standard SE output transformer, with no DC in the primary, I will get more power and bass out of it.
Cheers,
Alain.
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