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Re: [Amps] Acceptable ripple on high voltage plate power supply in tetro

To: amps@contesting.com
Subject: Re: [Amps] Acceptable ripple on high voltage plate power supply in tetrode amplifiers.
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 23 Dec 2024 20:03:04 -0800
List-post: <mailto:amps@contesting.com>
On 12/23/2024 4:46 PM, Michael Tope wrote:
My point was that by switching to CW or sending a pure tone on SSB, it would be easy to see hum sidebands on a waterfall or spectrum analyzer. As to whether any particular tube amplifier will generate hum sidebands, others have commented on the fact that class AB amplifiers have good anode supply rejection ratio compared to class C amplifiers. That isn't intuitively obvious to me, but I trust it is correct.

I do agree with you that using an SDR is a great way to assess ones signal quality.

Yes, and several of their capabilities combine to make very inexpensive SDR receivers vastly superior in some respects to the traditional frequency analyzers we've considered a gold standard for a century. The SVGA module for the Elecraft P3 spectrum display can achieve fractional Hz resolution. Using a lot of averaging, I would expect to be able see and even measure audible levels of hum at 60 and/or 120 Hz.

Here's work I did in 2015 with the P3/SVGA. Although I documented it in Power Point because it was easy to incorporate the screen grabs and comments, it was not intended for presentation.

http://k9yc.com/P3_Spectrum_Measurements.pdf

Here's work I did in 1986 using Time Delay Spectrometry, a measurement system invented in 1969 by the late Richard Heyser when he was at JPL.

http://audiosystemsgroup.com/AESPaper-TDS.pdf

Some of the more technically exploring minded in the pro audio world picked up on his invention, and implemented it with a stack of HP lab gear in the late '70s. In 1982, Gerald Stanley at Crown (the power amp people) developed a dedicated instrument to do both frequency analysis and time analysis using TDS, and I bought one of first units to come off the production line. Almost immediately TDS opened powerful windows in acoustic analysis of systems, transducers, and rooms, revolutionizing many aspects of pro audio and room acoustics!

Dick consulted with me on the project documented by the Paper, confirmed that my method would work, and told me he liked the paper when he heard it via a remote hookup to his hospital room, where he was to present his last paper on the same session. He was being treated for cancer, and died not long after. My test signal was embedded in the program material (an acoustic big band) at such a low level that you didn't hear it if you didn't know it was there.

73, Jim K9YC

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