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Old 23rd Jan 2022, 9:33 pm   #1
yestertech
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Default Hp8903b

I’m considering purchasing one of these as a fairly
‘Tidy’ method for measuring AF power output and distortion
There may well be alternatives but I would like something
With digital display rather than analogue metering.
Any suggestions welcome
Anyone got anything for sale ?

Andy
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Old 24th Jan 2022, 6:03 am   #2
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Default Re: Hp8903b

I've used them extensively for many years.

They just do what they say on the tin. No fuss. The only real advantage to the B suffix is a slightly more versatile input.

It has a little analogue meter with a rough scale, as an aid to peaking things.

Stewart of Reading seems to usually have one or two in stock, otherwise they don't turn up much. A 1980s HP box from the era when they made everything look all the same, so the bland looks disguise something quite special.

David
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Old 24th Jan 2022, 3:51 pm   #3
Max Power
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Default Re: Hp8903b

Some useful info here:

https://neurochrome.com/pages/hp8903

I've got an 8903B. A joy to use, mine came from Beryl at Stewart's, well, quite some years ago now...

Watch out which filters it comes with, as there are two option 'slots' which may be empty. Also, they come as front inputs, or rear inputs, so check first. Mine is front entry thankfully.

Also, it's a big beast, and takes up a lot of room on the bench.
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Old 24th Jan 2022, 5:16 pm   #4
mhennessy
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Default Re: Hp8903b

A big advantage of the B model not yet mentioned is the option to display dBu measurements.

The A model is dBV only. That means you have to subtract 2.21 from the readings if you want dBu. You get used to it, but given that dBu is near-universal in the professional audio world, it's a bit of a drop-off.

The lack of a CCIR weighting filter on the A model is also a shame. But then, there isn't a quasi-peak rectifier in the A model, so even with the filter, you couldn't use it for CCIR/ITU-R 468 noise measurements.

Ultimately, it's down to the application. For circuit design, it's fairly useful - distortion measurements down to -90dB (0.003%) are quite doable, though that's not all that demanding for modern audio circuitry, and an FFT tells you much more anyway. Being honest, I don't use mine as much as I thought I might.

But for doing a range of standard tests on professional audio gear with balanced inputs/outputs, the Neutrik TP401 is a better instrument, with a (mostly) nicer user interface. But relatively rare and expensive.

BTW, the 8903 can display power directly. There's a special key sequence that puts it into that mode, thus saving you having to manually do V-squared-over-R. I never remember it, so I just use a calculator, but after a while, I'll suddenly remember that the key sequence is printed on one of the two pull-out cards. But then, I'm just as likely to use a multimeter. And some of those can display dBm (so dBu if you tell it R=600, or dBV if you set it to 1k) as well as RMS voltage. A dedicated audio test set will do a better job with small signals, but for typical line level stuff, a DVM can be excellent (checking the AC bandwidth is important, of course).

This question came up before, with a similar end application in mind. The OP went for the 8903B: https://www.vintage-radio.net/forum/...d.php?t=136299

Whatever you pick, you'll need deep pockets!


PS: You've probably seen Pete Millett's software. Works well, but obtaining the IEEE interface might be a pain. I picked one up for about a tenner, but it only works Windows 95/98/Me, and needs an ISA slot. I subsequently found a PCI card, but IIRC driver support stops at XP. I haven't tried the various USB options yet.
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Old 24th Jan 2022, 10:44 pm   #5
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Default Re: Hp8903b

Beware of built-in GPIB cards. THe chipsets from Motorola and Texas each had (different) bugs in their handshaking protocols. HP GPIB cards used these parts.

National instrument did their own I/O chip and got rid of the bugs. So for a card slot PC mounted GPIB, you need the NI one.

Later on USB to GPIB cables were done with safe designs.

And the 8903 really gets into its stride with SINAD measurements for comms radio testing.

If you think the 8903 is big, look at the 8901 companion box (lf-1300MHz demod)

David
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Old 24th Jan 2022, 10:59 pm   #6
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Default Re: Hp8903b

I've got an 8903A and I love it. I use it more days than not. I combine it with a 3561A so I can check the spectrum up to 100kHz at the same time. Cross-check agreement between the signal level readings on the two instruments gives me confidence that neither has developed a significant absolute calibration error, which neither has over the best part of a decade or so.

Cheers,

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Old 25th Jan 2022, 2:21 pm   #7
mhennessy
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Default Re: Hp8903b

I'd probably use mine more if I didn't have other options. For basic use - such as checking the THD+N of a vintage amplifier that measures 0.1% or 0.05% at best, I'm more likely to use my Lindos LA1. It doesn't have the flexibility or resolution of the 8903, but it doesn't need it in that application. But what it does have, however, is the noise measurements that the 8903 lacks. And it has unbalanced and balanced IO, all ready to go with no need to use adaptor leads. Much quicker and easier.

I'd definitely use the 8903 more if it had a rotary encoder or two to control the oscillator. In fact, it might well become my default oscillator if that was the case. It's certainly the cleanest in my workshop. Such a shame that it's a pushbutton-only interface - a wasted opportunity.

This reminds me of a previous conversation about the 3314A function generator, which does have a rotary encoder, and is much easier to use as a result. Of this, David said "a competent function generator with a user interface like having a conversation with the world's worst pedant". So I don't think I'm alone in thinking the 8903 UI could be better

I have a 3580A, which is a lovely analogue beast with digital storage for the display. Not as quick as an FFT-based spectrum analyser, but a lot of fun to use. The dynamic range is reasonable at around 80dB, which is similar to the 3561A IIRC. Alternatively I do have a Tek AM7000, which is a bit of a beast and certainly has it's share of UI issues, but it does a good job for its age. I can borrow a Prism Audio Dscope from work if I need to go deeper still, but this is controlled by a PC, and I don't think I'll ever fully come to terms with the UI. But this is for design, where the overall THD+N figure is only a small part of the overall picture. For repair work, the Lindos LA1 covers most bases, despite its age and apparent simplicity. If I was to replace it, I'd pick the Neutrik TP401.

Of course, another large application is ATE. That's where the 8903 starts to shine, as it'll be controlled via the IEEE interface, rendering the front panel UI irrelevant. So someone in the design team had to decide what proportion of them would end up bolted in racks in Production, rather than on R&D benches - rotary encoders aren't cheap, after all...
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Old 25th Jan 2022, 2:51 pm   #8
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Default Re: Hp8903b

There was a trend in HP to have a front panel area with up/down buttons and if you were lucky an RPG knob. All the rest of the panel selected what this area did. There wasn't even a numeric pad on some.

When a manager tried to enforce this on one oscilloscope team he got the reply "The world isn't ready yet for a one-key piano with a pitch selector"

Utterly, utterly brilliant, and worth remembering should you ever meet that sort of idiot.

David
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Old 25th Jan 2022, 3:21 pm   #9
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Default Re: Hp8903b

I don't know what you're paying for the 8903B, but unless you really need a hardware option, modern soundcards are at a point where they rival the finest dedicated AAs.

Jan Didden sells a kit to make an autoranger - see here: https://www.youtube.com/watch?v=K4TRhEjaIcs

You can get a MOTU M4 soundcard (~£200) that'll give you THD+N on a par with a DScope! And if you spend more on an RME ADI-2 Pro, you'll have THD+N that rivals the top AP and R+S models. And unlike AP or R+S, you won't be tied into one SW package. The SW world is your oyster!

I use my Lindos LA100 every day - it's just so quick (and they are a nice firm - helpful and friendly). But you can't beat live FFT and that would be my desert island AA. I use an R+S for this, but R+S are now out of the AA game, so long term I am looking at a Didden + soundcard. One of the R+S here looks like it'll have to go to R+S for repair, and I'm dreading the bill... I am putting off emailing them...
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Old 25th Jan 2022, 6:39 pm   #10
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Default Re: Hp8903b

I am also a Lindos fan (the LA100 set = LA101 + LA102). Great support (still) from Lindos. Nice compact units, clear digital display, and lots of inbuilt sequences like sweeps, noise etc. XLR and jack sockets, and a printer interface for logging results. Good user manual (200+ pages!).
BTW if you need a set, drop me a PM as I happen to have some spare sets I have just done up!
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