[Amps] Acceptable ripple on high voltage plate power supply in tetrode amplifiers.

[Jim Brown]

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