Improving older test equipment

[anatech]

Hi John,
Thanks, but the shipping would kill me.

At this point, is there any reason to hide your actual schematics? It's an old design that depends on discontinued devices and careful hand construction. The PCB details are enough to stop a clone.

The reason I ask is that you could refer to specific design examples as you pointed out your design choices, or what you consider to be important concepts. It would be somewhat easier to keep things on track and clear to other people.

Considering the difficulties a normal person would have to begin production on anything, there really is not a lot to worry about there either. I do not want to make one of these, but learning from this would be very useful to many.

Just a thought John.

To create better audio devices, I think better equipment is in order these days. Sure, I can see all kinds of stuff using the gear I have now, but either a rebuild of my current stuff, or new equipment would be required to look at any cutting edge analog stuff that is current.

My problem is that I don't know where to begin to assess what to do with the existing circuitry. The guys at HP/Agilent know a heck of a lot more than I do about wide band, low noise circuitry.

Hi Scott, (or anyone else),
There is no reason why you would want to do this, but I'll ask if you have any ideas on how to improve the signal amps in the following HP equipment:

339A
3580A
3581A
3585A
or others that many people may have.

This would allow many more DIYers to get better measurements from equipment they already have. I would love to extend the service life and S/N ratio of these instruments. I imagine that the signal amps may be similar between some of these. I understand that John has improved his Sound Technology stuff, but that was op amp based, wasn't it?

Yes, a different thread. I just wanted to get Scott's attention. I asked Scott because I feel he has the knowledge and skill to pull something like this off. I imagine some other people would also have the skills required.

-Chris
Edit : Spelling

[Joshua_G]

Originally posted by anatech

Hi Scott, (or anyone else),
There is no reason why you would want to do this, but I'll ask if you have any ideas on how to improve the signal amps in the following HP equipment:

339A
3580A
3581A
3585A
or others that many people may have.

Also, Tektronix 2465B.
However, improving HP 339A will do me a great service.

[john curl]

For the record it is usually best NOT to attempt to upgrade HP equipment except for special examples, the 339 for example. It is better just to make a good low noise preamp and put it in front for difficult measurements.

[anatech]

Hi John,
Thank you. I was afraid of that. Still, I would like to keep an open mind about these things.

I wouldn't go ahead and work on one without a clear idea of what I needed to do. Even things like temperature compensation have been well thought out. I have a ton of respect for the engineers who designed this stuff.

There may be some small gains in working over some power supplies.

-Chris

[john curl]

Could you please try another thread? Experience is important in this case, and a reading of the schematics.

[john curl]

Let me talk about professional test equipment a little. HP, TEK, and many others make excellent test equipment and they do not go cheap on the parts. If they could find a part when the unit was first made or a different circuit that would give them better performance, they would have done so. Not true, necessarily in consumer audio or pro audio, and that is why it is easier to modify and improve.
To think that amateurs, or even professionals, without test equipment to measure noise, distortion, and voltage breakdown of individual devices, can easily and safely improve most professional test equipment is the height of folly, and if you were a soldier, the same mentality would quickly get you killed. That is why they have old sergeants to keep them in line. The biggest problem is usually self noise which can be higher than optimum. However, a X 100 gain, IC based low noise gain stage on batteries for low and difficult measurements, can overcome the vast majority of compromises in available test equipment. This is why I think that modifying a wave analyzer, or scope is a waste of time.

[Joshua_G]

Originally posted by john curl
For the record it is usually best NOT to attempt to upgrade HP equipment except for special examples, the 339 for example. It is better just to make a good low noise preamp and put it in front for difficult measurements.

Any recommended changes to the 339?

[syn08]

Originally posted by Joshua_G
Any recommended changes to the 339?

Joshua,

For a good number of reasons, this is way over your head. Leave it as is, or ask somebody which is skilled in HP service.

You can download the service manual from the Agilent site and do some lecture about.

[Joshua_G]

Originally posted by syn08


Joshua,

For a good number of reasons, this is way over your head. Leave it as is, or ask somebody which is skilled in HP service.

You can download the service manual from the Agilent site and do some lecture about.

No better Op Amps the original ones?

[syn08]

Originally posted by Joshua_G
No better Op Amps the original ones?

Not all of those opamps have the datasheets readily available, so finding better options is not easy. Most of them are in the old TO-99 round can, almost impossible to find today, so you need some sort of adapter (with added inductances and capacitances, depending on the chosen solution).

E.g. you can certainly find a replacement for LM348 (quad 741) but not so easy for the "1826-0487" opamp.

Perhaps some kind sould that already did and evaluated the upgrades will help you, otherwise this is not something you should expect for free. The costs in work and parts could be a significant chunk of what you originally payed for the 339A equipment. Then you have to recalibrate the instrument, another significant task, running the total costs up high.

So, one to another, you either have the significant skills and the time to DIY, or forget about. It's not a plug-and-go job.