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Opinions on HP3478A meter
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Old 14th June 2019, 07:24 PM   #51
Tubelab_com is offline Tubelab_com  United States
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I have zero confidence in anything I measure. Or my confidence is maybe 4 digits really.
Here in the DIY audio world, what could possibly require more than 4 digits? Maybe plotting the linearity of a 16 bit or more DAC, but even there relative numbers are more important than absolute accuracy.

I come from a 41 year career at Motorola and the last 12 years I was in an advanced development group which turned into an IC design group for the last 5 or 6 years......yes, some of my work there did need a whole bunch of numbers after the decimal point, but we had the budget for it.

Here in the world of vacuum tube audio on a retiree's budget, 2 or 3 digits is plenty. Spend the money where it's really needed......and that does not include boutique parts either.

Tuning up a voltage controlled music synthesizer for the first time....OK, I'll fire up the 3478A.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 15th June 2019, 08:02 AM   #52
suzyj is offline suzyj  Australia
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The slightly dim, flickering LCD on my 3478A was bugging me a little, so I fixed it.

First I disassembled the meter. It's not obvious how it comes apart, but once you slide the case off backwards, you remove the screws holding the transformer, regulator, and a couple of grounds. Then disconnect the rear panel connectors (2 x BNC, GPIB, and four rear banana jacks).

Then there are four little tabs on the front that pry up, and the inner part of the front pushes out of the bezel along with the whole PCB. Once that's done remove the display from the rear of the front panel, pop the plastic clips holding the display glass to the PCB, remove the zebra strips, clean everything with cotton buds and isopropyl alcohol and reassemble. Take note of the orientation of the display glass, as it goes back in upside down just as easily as right way up.

While I was in there I gave the plastic cover in front of the display a bit of a polish (light blue polishing compound with a calico mop), as it had a bit of a mark that hadn't been able to clean off.

I'm very happy with the result. The display is much more legible now. Actually the whole instrument is looking quite nice.
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Old 19th June 2019, 11:17 AM   #53
suzyj is offline suzyj  Australia
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Connected to a lab supply, with the 3458 also connected to compare the cal. The display on the 3458 updates quite quickly, but my phone camera freezes it nicely.

Not too shabby for a 30 year old calibration.

The only downside of putting it next to a new meter is that it makes it really obvious how yellowed it is.

Last edited by suzyj; 19th June 2019 at 11:36 AM.
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Old 20th June 2019, 03:40 PM   #54
rsavas is offline rsavas  Canada
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I'd say pretty damn good imo.
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