Oscilloscope HP 1720A

[Mermprin]

I have a chance to buy a HP Oscilloscope it is model number HP1720A. This is the description. Is this good for Audio Engineering?

The 1720A Oscilloscope is a precise, wide band (dc to 275MHz),
high performance oscilloscope featuring vertical deflection
factors of 10 mV/div to 5v/div with 2% attenuator accuracy.
Vertical functions that can be selected are channel A, channel
B, A+B or A-B. Input coupling can be AC, DC, 50-ohms, or
ground. Channel B may be inverted. It has a switch-selectable
50-ohms or 1 Mohm input with full bandwidth in either mode.
The main time base is calibrated from 10 ns/div to 5s/div in 24
ranges. The magnifier expands all sweeps by a factor of 10 thus
extending fastest sweep to 1 ns/div. The delayed time base has
calibrated ranges from 10 ns/div to 20 ms/div in 20 steps.
Delayed sweep automatically starts at end of delay period.
Internal triggering is stable in excess of 275MHz and requires
only 1 cm of vertical deflection and is selectable from channel
A, channel B, or composite. Trigger coupling can be AC, DC, LF
REJ, or HF REJ. Has a bright 6 X 10 div. internal graticule CRT
with post acceleration 20.5 kV potential. Also has a 1kHz
internal square wave calibrator.

[janneman]

This is IMHO a pretty good scope for audio work. In fact the wide bandwidth of 275Mhz is a bit overkill (unless you want to look at the outputs of your oversampling DAC).
If you ask me what I would want to change it is the vertical deflection sensitivity listed as 10mV/div. I would prefer that to be 2 or even 1mV/div to see noise and/or riple on stabilised supplies. But it really is gilding the lily, and if the price is right I would not hesitate.

Jan Didden

[Mermprin]

So I bought this. It is in really good shape. All Manuals and probes are with it. It used to belong to Amdahl, so I am pretty sure it had a good life. It does need to be calibrated so I will have to find a local shop to do that. Any other opinions from anyone? Price was good 100.00.

[janneman]

Congrats!

The calibration may cost (much) more than the instrument, be carefull. Check when the last calibration was done, there should be a sticker or something on the instrument.

Part of the calibration you can do yourself, except for the parts where you need a voltage or current standard or pulsgenerator. Even if you do those yourself with a good quality multimeter and /or a scope from a friend as reference, you get quite close and you save a lot of money.

Jan Didden

[kilowattski]

You should be able to get it calibrated for about $50. Calibration is a very competitive business these days. I used to work for HP many moons ago and I used to own a 1740A. All I can tell you is to get a can of good contact cleaner and clean every rotary switch in the scope. Those switches are the scopes Achiles heel, but keep them clean and the scope will serve you well. Congratulations on your purchase, use it in good health.

[Johnix]

Originally posted by janneman
This is IMHO a pretty good scope for audio work. In fact the wide bandwidth of 275Mhz is a bit overkill (unless you want to look at the outputs of your oversampling DAC).
If you ask me what I would want to change it is the vertical deflection sensitivity listed as 10mV/div. I would prefer that to be 2 or even 1mV/div to see noise and/or riple on stabilised supplies. But it really is gilding the lily, and if the price is right I would not hesitate.

Jan Didden

It's pretty easy to build yourself a x10 or x100 probe signal amp.

Using a low noise opamp with good noise level, it becomes easy to measure small signals up to 0.1mV/div with such oscilloscope (providing that you limit the bandwith of the amp)

I can post a simple schematic if you want

[Mermprin]

If you could post that schematic that would be great. I would be curious to check it out. Much thanks to all who replied !!!