HP 331A Distortion Analyzer
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- Опубліковано 16 вер 2024
- This is a delayed first look - By that I mean that I've had the 331A for a while but I've just never gotten around to cleaning it up and checking it for operation within manufacturer spec.
Let's take a look at it - Наука та технологія
Sorry to pull you up on this but you are not using the meter correctly, read the HP manual on operation of the unit. You were right till you didn't set up the level correctly (this is most important). Set the sensitivity switch course selector till the meter shows greater than 1/3 scale. Then use the vernier control to set the meter on full scale deflection if you require to measure distortion as a percentage , if you require a measurement in db adjust the vernier for 0 db meter indication. READ THE OPERATING MANUAL. Also make sure the meter range switch is set on 100% which is also 0 db. It can be switched to -10 db down if your signal is under 300 mV. The extra -10 db is then taken into account when reading of the distortion level.
I am an older ex Royal Australian Air Force tech and the 331A, 332A, 333A and 334A were used quite a lot.
Look at section III OPERATING INSTRUCTIONS of the HP operating & service manual. Most of the procedure is the same with all instruments except the 333A and 334A have a semi auto ability and can fine tune the notch filter accurately.
I own a 333A now but will need a little work, mostly pot cleaning and checking circuit levels against the manual and checking the cal as per the service manual. Regards Robert Scott
No problem at all - Thanks for the comment for both myself and anyone else that finds this - I clearly missed step H in the process (in section 3-18 of the manual as you pointed out). I think I got the rest of the process correct but please let me know if that isn't the case.
If you have any other comments regarding the videos/gear I'd love to get them - I use this stuff as a hobby rather than someone who used them for a job so it'd be insightful to hear about it from that perspective. Thanks again for the comment.
If I remember correctly all the RAAF techs were required to service equipment with the manuals out in front of them so no error could be made in it's use. This worked well in principal but human beings being what we are tend to skip things in order to save time. The balance controls you said you had problems with have to be set mid position before you start adjusting the notch filter but after you have minimised the output with notch filter taking the meter scale down as you go also minimise the output with the balance ctl, of course by this stage adjust everything extremely slow as the notch filter bottom out is extremely narrow bandwidth as it should be for meaningful distortion readings. I don't think I have used one of these since 1984 but yoy remember. I started with electronics at 12 way back in 1962. An electrical/radio apprenticeship starting in Jan-1965- to end of 1969 but I don't think I was able to play with HP test equipment till I joined the RAAF in 1972. I did my apprenticeship with BHP Newcastle NSW and most of their test equipment was primitive.
I was trying to ascertain your place in the world , I thought Canada or perhaps US but your spoken English sounds too good for these places.
Regards Robert
Thanks Robert - Really appreciate the comment - When I get a piece of gear that I haven't used, and most of these older HP items are in that category, I grab the manual from Dave over at Artek Manuals, read it and then try to ensure that I'm using the equipment correctly.
The problem I was having with the balance controls was that I kept wanting to treat the inner control as the fine instead of the outer control - However your comment regarding the slowness makes more sense of the arrangement now as you're going to need to use the larger control for better, well, control.
BTW I'm an Australian currently in Seattle WA - Been here about 20 years now.
OK mate well enjoy yourself over there, I lived in San Francisco (San Carlos) for several months with a girlfriend way back in the early 1990's and I was glad to get back home to Australia again. I guess in a nutshell just too many people for my liking. I repair electronic organs and play them, have been an organist since the early 1970's. I also repair a lot of test equipment, just bought a HP 33120A from ebay with issues, payed $202 AU so I hope it's repairable. I download service manuals, print them out and comb bind them (I have an A3/4 HP 5000 laser printer, actually two). There is a wealth of HP manuals on the net, the best quality ones coming from HP/ Agilent now taken over by Keysight. The thing is in electronics if you really love it you do not ever stop learning. When I look back to the 1960's when I was just a 12 year old looking at electron tube technology, everything was so simple compared to the technology of today. The basics are still there though, ohms law, power equations, ac theory understanding etc. I actually taught electronics in my later years in the RAAF so it's all stayed with me. It still is a wonderful hobby and I hope it remains so.
Kind Regards Robert Scott, Sale, Victoria.
+Robert Scott Good catch.. I was about to post basically exactly what you did about the level.. glad i looked first and discovered this was an older video and you had already brought this to his attention.. it's easy to miss a step or not quite get the operation right with a unfamiliar piece of equipment.. especially when you are used to more modern devices... these old manual units require you to think a little... think thats why i like my vintage equipment.. thanks for the great info... the gentleman seemed to appreciate the tips and it's good to see people helping people... i try to as well every chance I get.. sharing our knowledge is important, it's good to see others like yourself take the time to share... Thanks again..
Be aware the meter indicates RMS reading; which is correct for a clean sine wave. For a wave with complex distortions (more than just a bit of 2nd or 3rd harmonic), the meter becomes average responding. Thus, you will not be able to compare distortion measurements with a digital or more accurate RMS distortion meter. The manual briefly touches on correction factor, but it is not detailed.
If you have two signal sources, generate one primary fundamental frequency and then combine a second harmonic with the second generator (at double the frequency) at small levels to obtain 1%, .1% and .01% distortions. You 331 should measure them correctly. If you have a spectrum analyzer, you can see your levels. Otherwise, find a THD formula and do the math manually for your generator values to induce the harmonic value you wish.
Thanks David - In this case it was just the clean sine from the Arb - I should have video'd doing this with a larger more known distorted signal to show that the 331A reads the same as the 2015THD in that case.
Hit send a bit early - I ended up asking about how to get a known distortion value and it was clearly a senior moment on my behalf - Once I read the replies it was trivial to make a known value of distortion that had the 2015THD match the 331A on a sine wave - I didn't video that though and I've since sold the 331A so I can't go back and show that.
Thanks for the spot on comment though.
I fought with a HP 334 for a bit and it gave me a good education!
Cavi / conduttori Elettrici
Hi there - Sorry, I don't understand the comment - However if you have questions I'm happy to try and answer them.