HP 334A Distortion Analyzer

Workshop Project #16 - HP 334A Distortion Analyzer

This time, I have another - almost - vintage test equipment on my bench. I was looking for a distortion meter to check up on my occasional amplifier projects. Not that I personally care much about anything "beyond my hearing capabilities", but it's always nice to compare values between devices, particular between left/right channels of stereo amplifiers, where slight deviations might be noticable after all...

While browsing e-bay for something useful of that type, I discovered this HP 334A model. It was an affordable "as is" or "the light turns on" offer, and the service manual was readily available on the internet. MINE!

Join me in my fight against set screws, broken light bulbs, aged capacitors and empty camera batteries to find out if this device will serve me in future projects!

ADDENDUM: By now, I did read up a bit more on the definitions, and it seems that the device measures "THD+N" - it essentially puts a sharp notch filter in the fundamental frequency, that you can tune with the bridge, and the remianing signal (harmonics and noise) is what shows up on the meter.

ADDENDUM 2: Thanks to mikant71 for pointing out that a slight mistake made its way into the explanation process: During the distortion measurement, after adjusting the level, the sensitivity should not be changed; rather the meter range is the one that needs to be bumped to find the minimum value. My bad, that must have slipped by in editing several example shots together.

0:00 Intro / Presentation / Disassembly Problem
3:35 Cleaning
4:43 Meter Movement
6:35 Replacement Switch Handle
7:10 Case Information / Mains Switch
8:50 Sliding Switches
10:20 Potentiometers
11:25 Banana Plugs
12:42 Frequency Dial Assembly / Sliding Switch
14:35 Neon Indicator / Potentiometer mounting
15:25 A Tale of Two Grounds
16:26 Recapping
17:20 Black Box - LDR Setup
19:45 Front and Back Panel Mounting
21:23 Power Supply Test / Wiring Components / Knobs
23:35 Power On! / Calibration
24:35 Voltmeter Demo
25:15 Distortion Measurement Demo
26:24 Summary, Outtake

Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)

You can support me on Ko-Fi: https://ko-fi.com/atkelar

Thanks to Rik I have a nice replacement switch handle; visit his blog at http://justanotherelectronicsblog.com

Read up on the definition of THD on Wikipedia https://en.wikipedia.org/wiki/Total_h...