On Fri, May 29, 2020 at 12:50 AM, Reginald Beardsley wrote:
which is the best choice from a long term support basis, 7904 or 7904A?
what plugins? 2x 7A19 and 7B92 + ???
Hi Reginald,
Advantages of the 7904A over the 7904:
- Newer, so possibly less failure-prone
- Easier to service because of split construction
- Front panel layout very much like the 7104 (or is that a disadvantage?)
- Internal construction and components very much like the 7104
- More modern look (to some at least)
Advantages of the 7904 over the 7904A:
- Fewer hard-to-get components
- No fan (a huge advantage according to some)
- Backlit Vertical Mode and Horizontal Mode buttons
- More versatile calibrator, includes current loop
- Can be had for very little money
Make sure that in either case, you buy one with the Alphanumeric screen-readout, which is standard.
It's very difficult to determine the better choice on long term support aspects: Do you want a younger and therefore possibly slightly more reliable instrument with more expensive, hard-to-get components or do you want an older, slightly less reliable instrument with fewer and cheaper hard-to get components? If you have room to spare, have 3 7904's for the price of one (or 2) 7904A's.
As regards plugins: For general-purpose work, put in a 7A26 (Hi-Z, 200 MHz) and a 7A19 (Lo-Z, 50 Ohm only) or, preferably, a 7A29 (resettable overvoltage protection, continuously variable attenuation), a 7D15 counter in the A Horizontal slot and a 7B92A into the B horizontal slot. Make sure you have all the other plugins nearby (7A13, 7A22, a sampler system for > 1 GHz).
Both have a switching supply. Apart from the well-known lifetime-driven weaknesses like electrolytic (mains voltage buffer) caps and tantalum (bead) caps, I'm not aware of any structural vulnerabilities.
I concur with Dave D. re. the 7854. It's more complicated and therefore more vulnerable but it's also one great piece of equipment, especially if you use sampling plugins.
Raymond
Raymond Domp Frank