# Fixing up older equipment for new projects!

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Hi all,

I did not see an equipment support section, and I am working at home with basically small budget and for the pleasure of the science and electronics, so I'd like to ask if anyone has a tech manual for these older equipments. I build or modify a lot of my own electronics when it's not available or otherwise too expensive for a hobby purchase.

If this is posted in the wrong place, please excuse me and mods can move or delete.

1.) Spectromagnetics NMR Gaussmeter model 5300 (Spectromagnetics - The Cyclotron Corporation) - same thing, need the whole manual and schematics on this one, and a magnetic field probe for it.

Worst case I could make a probe if I have the manual. It's much more complex than the amplifier below, and there is something wrong with it so the book would be a huge help. Otherwise, I don't think I can fix it.

The purpose of the instrument is to use with a NMR spectrometer I am working on. I already built it on my workbench, but it took up the whole bench, so now it's time rebuild the same basic circuit in a rack cabinet. I want to look at periodical or RF variations in the magnetic field. I'm sure there will be other uses for the Gaussmeter if it can be repaired.

2.) Geotech 4983 helicorder amplifier. It's just the amplifier, which I would like to repurpose.

I don't have the drum recorder, but don't really need it (wouldn't turn it down..). This is an old chart amplifier with vacuum tubes. That's no problem but I am looking for the schematic diagram or manual if anyone has it. That would save me several hours tracing it out, plus help me calibrate it.

The re-purpose of this instrument amp is to drive a direct coupled power amplifier stage running on an adjustable +/-50 to +/-200V supply. The whole instrument will be able to amplify an arbitrary waveform to a range of outputs covering as much as +/-200V and +/-1A (3A peaks). It will hopefuly give a linear current waveform or linear voltage waveform (switch selected) into a variety of nonlinear loads from 100 Ohms up. For me, it's a lot faster to modify something that is similar to what I need, than to build everything from scratch.

Thanks!

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you don't need a manual to fix that.

you need betty boop.

it may be cheaper to build your own than to find replacement tubes.

http://www.tubesandmore.com/

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Betty was well before the time of these tubes. This is a 'modern' tube chart amplifier 8-). The spectrometer is solid state except the CRT. I have spares. I repair and hack a lot of this old stuff and enjoy using it.

I have the tubes on hand for the amplifier, they are very common. Tubes are available pretty cheap on the internet, even used one are available, tested and guaranteed.

The mistake many people make when using tubes is choosing the familiar audio output and preamplifier types. Those are always costly because they are popular. Consumers are stuck with the $40 tubes that came in their hi-fi or guitar amp, because they do not know how to select tubes. That's where I pick the$6 tube and change the operating potentials and circuit values where necessary.

Anyway, the information would be useful on those equipments..

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yes, i have a few friends that swear by tube amps.

is it the warm sound you don't get from a mosfet?

i wish you luck on your journey.

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Thanks! I like the way push pull tube amps with output transformers sound. A good one can be driven hard and not sound as distored or unpleasant as the more acurate clipping from solid state amps. Others swear by single-ended transformer-coupled ones (I think the warm sound is more from those). A few prefer tube amps that are direct coupled to speakers. Their output topology is like a non-complimentary semiconductor amp. There are scientific reasons why those amps all sound different. It's a matter of taste which an individual prefers. I also like the sound of AM oldies stations emanating from a big old wooden cabinet radio, but it's absolutely not hi-fi. So, little things have a tangble effect. It is also possible to get a MOSFET to sound much like a tube. It is the circuit topology that contributes greatly. All music is colored by the reproduction system. I have always spent the most money on speakers, and picked the ones that sound best to me, because the human hearing and the way the brain interprets it is so different from one person to another that the only thing that really matters is what sounds good to an individual. It's good to have choices.

It's always the discrepancies in the interfaces between forms of energy that make an individual difference in perception of entertainment. The speaker, the antenna, the lamps, the microphone, the projector, etc. Lab gear for science on the other hand tries to eliminate such discrepancies when converting or measuring. So that's what my projects here (with those two items) are about.

I found a site offering that gaussmeter with a probe, but it wasn't cheap and they didn't have the manual for the instrument on-hand.

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Thanks! Sad to report a couple of those links are just link farms now. Seriously, I had inquired to the existing places on that listing and many more, but no one has these books. I thought I'd try here as it's a science site on the chance someone had access to dusty old volumes. I'll stick around and read the topics anyway, maybe learn something. It's been a long time since my schooling 8-)

Edited by Opcom

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