Looks like I forgot what I used to know. The HP analyzer works by placing applying the input signal to high-Q notch filter, and then measuring what is left over when the filter is tuned to the signal's fundamental frequency component. More of a selective attenuator than a subtractor, this method eliminates the need for a high-purity sine wave oscillator.

ak

 

Looks like I forgot what I used to know. The HP analyzer works by placing applying the input signal to high-Q notch filter, and then measuring what is left over when the filter is tuned to the signal's fundamental frequency component. More of a selective attenuator than a subtractor, this method eliminates the need for a high-purity sine wave oscillator.

ak

That would be my memory of the 332A. Additionally before auto tune, well after also I believe, there is a front panel output so once the fundamental is tuned the front panel out affords the hum and noise out. Using a scope one can have Harmonics, Hum and Noise. Pretty nice units back then.

Ron

 

We had a short rack on a roll-around work cart, that had the 334, an HP rack-mount storage scope, and a low distortion oscillator. It was a nice rig, particularly capturing the distortion products output on the storage scope. 100% analog, and very few opamps.

ak

 

https://www.amazon.com/T-king-Automatic-Distortion-0-01-30-Frequency/dp/B08MK168MS/ref=sr_1_105?crid=3PLCJE2B91694&keywords=Total+harmonic+distortion+meter&qid=1640713885&sprefix=total+harmonic+distortion+meter,aps,103&sr=8-105
This comes pretty close to what I was looking for.

Sorry, late to the party. Similar in shape to what you are looking there are the Meguro units - the MAK6571 is common in certain audio circles, but it is indeed more limited than the full audio analyzers such as the MAK-6630 or the HP 339A