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unmodulated carrier waveform on a Bauer 707 1kw class c transmitter




 
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Author Topic: unmodulated carrier waveform on a Bauer 707 1kw class c transmitter  (Read 600 times)
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kc4mne
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« on: May 07, 2019, 11:23:59 PM »

Hi Guys,

Working on my Bauer 707 conversion to 75M. The attached picture is of the rf output waveform without modulation. I am assuming that I should not have a perfect sinewave since the rf deck is running in class C. My output tank is a Pi-L setup and this is the waveform with the tune cap at the point of plate current dip. Load cap set to load up a 900 Watt output.

I bring up the tuning since adjusting does change the waveform, as expected since that is what is filling the gap while the tube is not conducting for 180 degrees in class c


My question is: IS THIS HOW THE WAVEFORM SHOULD LOOK, or is something wrong ?

Thanks
Manny
KC4MNE


* carrier.jpg (129.63 KB, 768x1024 - viewed 110 times.)
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« Reply #1 on: May 08, 2019, 01:07:23 AM »

A PI-L net output should have a sine wave.

Here is some info from Guyger:



Phil - AC0OB

* BAUER 707 Pi Net.pdf (41.92 KB - downloaded 86 times.)
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Patrick J. / KD5OEI
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« Reply #2 on: May 08, 2019, 06:09:20 PM »

3rd harmonic?
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KK4YY
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« Reply #3 on: May 08, 2019, 06:48:46 PM »

AC coupled scope input?
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kc4mne
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« Reply #4 on: May 08, 2019, 09:57:26 PM »

Thank You Phil ! I had the full set of Guyger's mod drawings which I have studied a hundred times. I only did an 80M conversion, but I was using the same values for C L C L EXCEPT I was tapping the inductors and leaving the unused portion not connected.  When you sent me the schematic and I looked at it again I noticed how the fixed tap for 160 was connected, effectively shorting the unused portion of the inductor.  Went back and did that and I have a beautiful perfect sinewave.  It is a happy day !! Smiley Smiley
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« Reply #5 on: May 08, 2019, 11:52:47 PM »

Thank You Phil ! I had the full set of Guyger's mod drawings which I have studied a hundred times. I only did an 80M conversion, but I was using the same values for C L C L EXCEPT I was tapping the inductors and leaving the unused portion not connected.  When you sent me the schematic and I looked at it again I noticed how the fixed tap for 160 was connected, effectively shorting the unused portion of the inductor.  Went back and did that and I have a beautiful perfect sinewave.  It is a happy day !! Smiley Smiley

Good deal!

Without shorting the rest of the inductor turns you get circulating currents, along with the inductance's distributed capacitance, oscillating at one or more frequencies, which the scope was showing.


Phil - AC0OB
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