I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy
Is it just the switches, or is the display quality becoming worse too? At some point we should probably start a separate thread about repairing those modules and extending their useful life. The NewScope5 is very cool but, as you say, pricey.
I thought it would be worthwhile to mention a few things for those readers not familiar with the 3577A. Measurement-wise, it set a new standard of accuracy and performance for VNA's in its freq range. The main thing a VNA needs to be able to do is measure inter-channel magnitude and phase differences over a) a wide freq range, b) offering a wide range of suitable filter bandwidths, and c) over as wide a dynamic range as possible. These areas are where the early VNA's had limitations.
Take dynamic range. Up until then, VNAs had amplitude accuracy of +-0.5dB and phase accuracy of +-1.5º over a
60dB dynamic range (below full-scale), and only at mid-band IF's and frequencies. Max freq range was in the 10-30MHz range, and smallest IFBW was 3Hz (and not very stable). HP 3570A and Anritsu MS420 are examples of this.
The 3577A comes along and betters everything by an order of magnitude, with worst-case amplitude accuracy of +-0.08dB and phase accuracy of +-0.5º over the same
60dB dynamic range, extending it to amplitude accuracy of +-0.25dB and phase accuracy of +-1.5º over an
80dB dynamic range. And doing it at ALL IF's and frequency ranges. And offering a stable 1Hz IF and 5Hz - 200MHz useful bandwidth in the process. Remarkable.
It was an incredible work of engineering, both analog and DSP. And HP sold a ton of 'em.
The fact is, the newer VNA's don't perform any better over this same freq range. 25 years later, and it is still as good as it gets accuracy-wise.
My main beefs with the 3577A are:
: The noisey fan is almost unbearable.
: The display is too small and crowded, with poor contrast. Causes eye strain for me.
: Scattered user interface. Control grouping reflects the underlying firmware organization, not the best ease of use.
: Like most instruments from that era, its big and heavy. But it was best possible at the time.
: No built-in power splitter. A silly omission.
: No AC coupling option on the inputs. Another silly omission.
: Output and all inputs are bonded to chassis ground, requiring isolated/diff probes and/or use of output xfmr for ground-isolated low-level measurements.
: 1 Hour warmup time for stated accuracy. The instrument will spend 1/10 of its life warming up for use
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
But considering that you will have to pay royal sums to find something that improves on these things, the 3577A is an incredible bargain.
EDIT: and worth mentioning... the 3577A has no firmware bugs I am aware of... I've never encountered one.