Are all amps being built wrong?

@jasonbourne52 - It's been a couple years so I would have to look at that Harvard H3 again. I seem to recall 1" long beads, but they could have been rods. They were all around the power tube sockets.

@bdp24 - I'll see if I can dig something up to verify. I keep forgetting those AC circles are still accessible although AC banned Roger.

@atmasphere - I have about 3 hours (cassette tape) of Roger interviewing Julius Futterman (also interviews with Saul Marantz, Sid Smith, and Brian DePalma) that he recorded when visiting Julius in NY years ago. Upon opening the door to his shop Julius asked Roger if he could come back in an hour as he was about to get started eating his lunch (which he brought to work everyday in a brown paper sack). BTW - if you are interested in dissecting an H3 I have two of them. I'll send one off to you if you like. Perhaps we can find out if he was able to pull off that 60 dB of feedback.

@clio09 I'd love to see it!

United States Patent Office. 2,773,136. Patented Dec. 4, 1956. 2,773,136. AMPLIFIER. Julius Futterman, New York, N. Y.

This invention relates to amplifiers, and more particularly to audio-frequency power amplifiers employing large amounts of negative feedback to reduce distortion, and is therefore useful in the reproduction of speech and music...
One object of my invention is to provide a low cost power amplifier that does not use an output transformer, and is capable of Supplying large amounts of undistorted power directly to a low impedance load of the order of 16 ohms, such as the voice coil of a conventional loud speaker. Another object of my invention is to provide a power amplifier useful over the audio range of 20 cycles to 20 kc. and capable of utilizing large amounts of negative feedback, of the order of 60 db, without instability.
United States Patent Office. 2,773,136.

This isn’t quite correct, just so you know. Try putting your amp on a Sound Lab ESL sometime.

One of my business partners at the time had West Sound Lab monsters and used, of course, my amps. Sounded terrific (all speakers are, of course, to someone’s taste). no issues whatsoever. Just sayin’

Edit, after some coffee, do remember back (oh, 300 posts ago, i get it :-)) that my designs are not zero output impedance. Since they do not use global feedback, there is always *some* meaningful output impedance, but also, pretty much zero chance of instability.  Both often issues with large 'stats.

I also did not measure their spectral output, just listened.  using my favorite measurement aid of the time, single malt scotch.

Now would someone prefer quickie's or yours? maybe.

United States Patent Office. 2,773,136. Patented Dec. 4, 1956. 2,773,136. AMPLIFIER. Julius Futterman, New York, N. Y.

Thanks!

One of my business partners at the time had West Sound Lab monsters and used, of course, my amps. Sounded terrific (all speakers are, of course, to someone’s taste). no issues whatsoever. Just sayin’
Edit, after some coffee, do remember back (oh, 300 posts ago, i get it :-)) that my designs are not zero output impedance. Since they do not use global feedback, there is always *some* meaningful output impedance, but also, pretty much zero chance of instability. Both often issues with large 'stats.

I forgot that the Sound Lab has adjustments on the back to allow for more bass and less treble. Anytime you see that sort of thing on the back of the speaker, its an indication that the speaker does not conform to the voltage rules. It has the adjustments to allow the unknown output impedance of the amplifier to work with the speaker (IOW they are not there to adjust the speaker to the room). So that was not the best example on my part.

Running zero feedback is a nice way to insure stability. What is the output impedance of your amp?