Hewlett Packard HP 334A Distortion Analyzer 2 of 2.MOV

[@jspencerg]

Thanks for the good demonstrations. I just got a working 334a.

[@ElPasoTubeAmps]

It is a nice instrument. I should have kept mine but I traded my off years ago and got into FFT analyzers for audio that runs on a PC.

[@ElPasoTubeAmps]

The back-and-forth nulling procedure is to completely null as much as possible the test frequency - say the 1 KHz signal you are injecting into the amp that's passing through to the output. We are measuring at the output of the amplifier so after suppressing the fundamental (test) frequency what's left are the distortion (harmonic) products created by imperfections in the amplifier. The analyzer displays the sum of all of these harmonics giving Total Harmonic Distortion (THD) on the meter.

[@RadioNJ1948]

The RF Detect switch on the left was for AM radio station use back in the day when the FCC required “audio proof of performance “ annual testing. The RF detect input BNC is on the back. In use an engineer could connect an RF sample from their transmitter and then read THD on the 334A. I personally never used the RF detector in the 334A and preferred to use the station’s modulation monitor audio output instead. Many hours in wee morning hours behind the 334A. Still have one. Still works very well.

[@ElPasoTubeAmps]

Philip, Really nice for you to add this bit of information. Otherwise, most of these details are going to soon be lost to time, certainly one of the reasons I post videos on these old instruments to help prevent this loss of knowledge. Now I almost wish I still had mine as I operate a homebrew AM station on the amateur bands. I do have a fancy PC based program that takes a sample of RF off the line and monitors positive and negative modulation peaks. I use a "keep-alive" voltage source and peak limiting circuit that actually works very well where positive peaks can go well over 100% but the negative peaks can be set to never exceed 100% by varying the keep-alive voltage source. Thank you for your comment.

[@RadioNJ1948]

@@ElPasoTubeAmps Thanks. I enjoy your work with tube amps. I have a. Harmon Kardon Citation II I’m getting ready to rebuild. I had this for almost 50 years and stored away to someday repair/re cap it. The envelope detector in the 334A works all the way to 6 meters. So perfect for checking distortion on an AM ham rig. Unlike BC transmitters Amateur Radio AM rigs don’t seem to like continuous sine wave testing. Watch for over heated transformers etc.

[@benadams6332]

Thanks for the demonstration. The way the distortion analyzer works is that you adjust a notch filter filter through the procedure you demonstrated to remove the fundamental frequency. Once the fundamental is notched out, all that is left is distortion and noise.

[@nicholasbove6141]

Your problem may be capacitor related. More specifically film capacitors. I have a bunch of old rack mount hp test equipment, just recently I got a HP 500BR frequency meter that was WAY out of calibration on the higher frequency. I replaced all the film capacitors with high precision cornell dubilier and vishay sprague in the range selector switch and after recalibrating it work beautifully now.

[@ElPasoTubeAmps]

I would love to have the HP8640B as my Wavetek 3001 quit and I can't seem to fix it. Not really sure how to help you as I have never done what you are doing. I would start by putting the FM generator modulated at say, 1KHz through the tuner and see what I read on a distortion analyzer at the output. Not sure what to expect but I wouldn't be surprised if it was at 1% or so and that might be OK. Maybe carefully start the alignment procedure from there ?? Hope this helps.

[@ElPasoTubeAmps]

Thank you - it is a bit labor intensive and for that reason I tend to make less measurements but I agree that it is beautiful and that is why I keep it. It is as accurate as the digital equipment and it has a very nice analog audio voltmeter The Tek equipment seems to be the most accurate (in my opinion) and is microprocessor based but the HP 8903A/B is the way to go. I got mine for $530 for the 8903A and USB/HPIB interface.

[@ElPasoTubeAmps]

The HP 334A style is nice but tedious if you want to mearsure many points. Best ultra low distortion oscillator I have found is the Tektronix SG 505 - plugs into the TM 50x series modules. I test at 1KHz initially for max power, clipping level and sine wave distortion then move to 30 or even 20 Hz at the low end and 20KHz or more at the upper end. 400 Hz would be a good point also. I am not familiar with anything but the HP and Tektronix distortion analyzers. There may be better instruments.

[@philipiano001]

Many thanks, Excellent training videos for us novices. Best Regards.

[@BoredQwerty]

Very beautiful machine! Thanks for explaining how it works! I was so afraid that digital distortion meters could be much better, but this works just awesome! Not so fast measuring but really interesting. I hope I can get one cheap on ebay soon

[@gmcjetpilot]

Great video and JUST what I need. I have a mechanical engineer degree but restore tube radios and amps for a hobby. I want to get a distortion meter and was looking at the HP 334A. I have HP and Tektronix gear test gear. I am more into RF than audio, but I want to expand into FM stereo alignment, thus the need for audio gen and distortion meter. It seems a low distortion audio gen is needed. Suggestions? Also what is the common benchmark audio Freq test are done for amps? 400 Hz or 1000 Hz? Thks

[@hightttech]

Very enjoyable video 👍.

[@Mephysto65]

Great video as usual in your channel. I recently bought one of this. How can I test it's efficiency using oscilloscope and signal generator? Thanks in advance

[@gmcjetpilot]

Also I was thinking if you are trying to make an adjustment of MIN distortion does it matter what the absolute value is. If you are not trying to meet or measure factory distortion than it can still serve as a tool to adjust say a radio for min distortion. With that said I don't know much about distortion. What are good distortion numbers for a radio, amp and other audio sources and devices. I assume the speakers are the big distortion adder. Also can the ear even hear this?

[@blazedsilence]

How exactly do you read the dB scales in regards to distortion? Do you just add or subtract the meter range indicator on the meter dial from the reading on the meter?

[@coldfinger459sub0]

I’ve been watching your videos for the past few years and just started building my own amplifiers in investing in equipment. I’m now at a point where I want to get my own distortion meter and was thinking of one of these old units as my first one to get my feet wet and learn the basics even though it looks time-consuming doing everything manually.

[@ElPasoTubeAmps]

Good distortion numbers would be considered by most to be 1% or less in the playback system. Distortion at 10% or more, generated by the guitar amplifiers, are not uncommon in the creation of music and may be desirable to the player and audience. Distortion may be intentionally introduced at low level (in the voltage amplifier stages) or at high level by clipping in the power amplifier by overdriving it. Playback within the stereo system with distortion that is reaching clipping is undesirable

[@gmcjetpilot]

@essoterric I ask because I have a HP8640B signal gen that produces FM (from an internal or external input). The specs from manual & measurement by other owners is about 0.3% distortion (0.2% for internal audio), so total of 0.5%. If I use a low distortion "stereo gen" to drive the audio, total 0.3%-0.4%? The dedicated FM Stereo RF signal Gens advertise 0.1% or more. I read distortion can affect alignment & separation (vintage stereo FM tuners). If you want to sell the 334A let me know.

[@danielh4995]

They are good units I use a 333A which is basically identical to the 334 to do just what you are intending, I know this is an old post and you have probably solved your questions by now but my weak link in the chain is the FM signal generator and getting it to produce a consistent frequency, just something to watch out for.

[@philhemenway3503]

What is the purpose of the 600 ohm load? Thanks.

[@ElPasoTubeAmps]

+Phil Hemenway Depending on the equipment, many pieces of test equipment require an external load so that the dB scale is calibrated almost always 600 ohms for audio and 50 ohms for RF equipment. For cable TV systems it would be 75 ohms. If you don't use the external load the voltage will be double and your gain/loss measurements won't make sense. It usually doesn't affect the distortion.

[@brandonclayvon2320]

Can someone tell me what this actually does, i think I get it but can u reverse this by adding more distortion if you want for creative purposes

[@ElPasoTubeAmps]

Its purpose is to identify the level of Total Harmonic Distortion (THD) and it is typically used to help reduce THD in an amplifier. Using it to increase THD for creative purposes would probably not be a good use for this instrument as it gives - Total - harmonic distortion. You would want to use a spectrum analyzer which will clearly display each individual harmonic and its amplitude so maybe you could "tune" an amp for desirable and undesirable harmonics.

[@brandonclayvon2320]

Thank you for the information