Question on a Pre-amplifier for a 3He

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Dennis P Brown
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Re: Question on a Pre-amplifier for a 3He

Post by Dennis P Brown »

Well, if I didn't have bad luck, I'd have no luck. I purchased their circuit board designed for that CSA chip - the chip is pushed into that mount. However, the mount's vertical standoff wires bent over. I removed the chip and tried to bend the mount back to vertical but its attacking wires broke immediately. Unbelievable - first, why have the chip mount as a stand-off? Then make the wires extremely flexible but apparently instantly work hardened? Never had such an issue with any chip mount I have ever used previously (nor ever had one that was a standoff) - otherwise, the board is top notch so I am lost why they made such a terrible choice in how to mount the removable chip - a stand off makes zero sense.

Also, the chip pins appear lose in the circuit board mount (!) The chip mount they have does not in any way or manner enable the chip pins to seat in a firm manner (hence, easy to push down so the mount bends.) A very puzzling design all around - Amazon claims it is sending a new one and I just have to take the other to a UPS store and they will package and ship it. If so, that is a very good policy.
Rex Allers
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Re: Question on a Pre-amplifier for a 3He

Post by Rex Allers »

Hi Dennis,

I'm just trying to understand your description of what happened.
Is this the board you are describing?

CR-150-R5-photo.jpg

If so, that in-line socket in the board center with 8 gold receptacles is what folded over?

Those look like AUGAT type sockets, which are very high quality connectors, but they can be tight if the thing you are plugging into it has any width to the pins. Any hoo, I guess that black strip with the gold receptacles folded over sideways?

Bummer. Looks like it was soldered to the board in a surface mount fashion. Never would have happened in the olden days of through-hole mounting.

Alas, you seem to be a victim of progress.
Rex Allers
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Dennis P Brown
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Re: Question on a Pre-amplifier for a 3He

Post by Dennis P Brown »

Yes - that is the board and the soldering so it is a 'stand-off' mount makes zero sense. The chip doesn't even go in tight - just a lose insertion. Otherwise, the board is very well made - just hard to fathom that design.
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Richard Hull
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Re: Question on a Pre-amplifier for a 3He

Post by Richard Hull »

Playing catchup here..... Was the board an extra cost item or was it supplied with the 110? If extra, how much extra?

Being an electronics person I would have just bought the 110, no board. Those augat sockets are not deep and never an extremely tight gripper like a formal IC socket or a formal header plug.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Question on a Pre-amplifier for a 3He

Post by Dennis P Brown »

Being rather electronic phobic when it comes to making circuit boards, I bought their commercial version. I am shocked that the chip socket/mount is worse then useless compared to any chip mount/socket I have had experience with previously. It is good that Amazon replaces a defective item free but that does not solve the issue of the chip socket lacking good characteristics required in order to hold a chip.

In any case, I am deeply concerned that the existing socket simply does not allow a firm insertion of the chip's pins - those pins are not tightly held and this worries me.

I could use conductive epoxy (under 0.2 ohm conductance) to hold the chip in the existing socket but that is not reversible nor replaceable. Best course might be to buy a better socket and solder that into the existing socket. Then insert the chip into a proper socket. Likely it will be difficult to find a proper socket but well worth the effort if said mount actually tightly grips the chip's pins.

Just a weird problem that I never expected with what appears to be an otherwise well designed & mfd. circuit board.

Update: I've decided to get an inline 8 pin socket (should fit since it matches the chip's pin spacing) and install that into the existing socket on the circuit board. Hopefully the new socket I've ordered both fits well into the existing socket and holds the chips pin's tightly. I have the silver epoxy if any of these pin/sockets systems are not tight enough.
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Dennis P Brown
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Re: Question on a Pre-amplifier for a 3He

Post by Dennis P Brown »

Decided to build a voltage regulator (LDO; +/- 9 volts) for the CSA and the battery supply. Yes, I will need at least 12 volts (due to drop out and my deciding on +/-9 volts rather than a lower voltage - seemed simpler ... .) So now I can't use a single set of transistor batteries but I guess that is the price of trying to build something that isn't commonly used.

Interesting that a negative 9 volt LDO regulator is extremely rare compared to positive ones. Digi-Key offered just one that could be delivered in three days. The other two required 7 or more weeks - this caught me by surprise. Yes, I could have used a lower fixed voltage output but due to drop off, I felt I was looking at something more like 7 volts and that worried me as being too low. So it just seemed simpler to just go with +/- 9 volts fixed output and use more batteries.

Speaking of which, can two transistor batteries be ganged together and the cases grounded in order to get +/- 18 volts? Or is a battery ground on a post an absolute requirement (i.e. the battery floats)? These are issues someone without electronics knowledge often can't easily find an answer since the logic of this is rather diffused in texts. Certainly not in E&M books - nothing practical in those ;) Guess that is why they use it in physics - lol.

Finally, are all 'minor' and almost turnkey projects in digital electronics always this tasking relative to simple parts?

Quick update: Amazon was true to its word and the replacement CR-150 board arrived; I drop off the broken one at UPS and they'll pack it and ship it for free. Now I will see if I can add the pin holder (once that arrives.)
Just discovered, it takes a huge force to get the pins to seat - that is a terrible design. Tested using a single pin and yes, it seated. With that raised for the chip (stand off wires) it is no wonder the mount can easily bend and and if straighten, breaks. Beware of this issue if anyone else buys this board for the chip. Yes, now I see that making your own has a lot of merit after all.
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Richard Hull
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Re: Question on a Pre-amplifier for a 3He

Post by Richard Hull »

I am one of those Q&D folks in electronics (Quick and Dirty) I attach how I would do it. No socket, no PC board, but a custom built box designed to let the circuit CR-110 free float in air with near zero length connections within its shielded box either with or without batteries. I just happen to have the teflon standoffs on hand, but the smart among us here could craft their own. Every thing else is easy other than the custom box.

Richard Hull
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CR-110 preamp box.jpg
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Question on a Pre-amplifier for a 3He

Post by Dennis P Brown »

As always Richard, yours's is a vastly superior design* to the junk ... I mean, commercial board . That is a great approch - I really appreciate the no circuit board design! (Why I didn't think of that ...oh, yeah. That's right, I am a non-practical novice.) Wish I had seen that before all this started. Now that I've seen that design I am seriously considering I might have to revert to that at some point (as in after this test with the 3He in a week or so - depending on when the new HV cable arrives - it is currently in NJ, at least.)

I had a small enclosure and connectors (HV & SHV.) The mistake I made is that my 3He detector is a female HV coaxial connector and my box connectors are also female. For the HV input that is fine but that makes connecting the detector an issue - currently, I will need another cable. Otherwise, I need a male-male coupling which is the proper solution - just a few weeks for delivery from China when I try that route.

The install for the box was ridiculously complex and a real pain - of course one of the chip pins bent while seating (unbeknownst to me). So, after assembly I noticed that issue and that required a partial disassembly in order to remove the chip. Luckily, no issues bending it straight and reseating the chip. Never has any project caused me such issues (not that I've done many.) What I really dislike is that the enclosure is very tight and wires have to be in exact places so as not to risk HV arcing.

* That approch you posted should be placed in the FAQ section for Neutron detection for a pre-amp design build. It really is a marvelous approch that others would certainly be well advised to copy.
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Front box with two HV connectors; the test, Sig. and the SHV Input (Det. on side not seen)
Front box with two HV connectors; the test, Sig. and the SHV Input (Det. on side not seen)
Inside wiring (He Detector HV connector on right)
Inside wiring (He Detector HV connector on right)
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Richard Hull
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Re: Question on a Pre-amplifier for a 3He

Post by Richard Hull »

Your design look great! Just remember, the box is ground and clearance must be allowed for the HV bias portions of the circuit to not arc to the box or other nearby ground parts of the circuit. Bias input SHV BNC part of the preamp is typically on the preamp output end of the preamp box. (traditional)
3He tubes bias rarely reach 2kv while some BF3 tubes can soar to over 3KV

All the very best on your finished product.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Richard Hull
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Re: Question on a Pre-amplifier for a 3He

Post by Richard Hull »

In the "floating CR-110" diagram seen in my above posting, I suggested standoffs for the full voltage of the bias where bias HV components connect to avoid arcing from these components to grounded chassis parts or other grounded circuitry.

At the hamfest which I attended today, I found a man selling huge amounts of these standoffs!! Their official name are turret post standoffs.
I attach an image of the two types I purchased for a buck a bag. These should easily withstand 3kv off chassis ground. ( I will test)

They are both 4-40 thread items. The blue ones are probably nylon or delrin. The ones I like the most are the steatite (ceramic) turret posts, though both are fine.

I just thought you might like to see what to look out for at hamfests. I recently saw 4 of these for $4.95 in a discount sellers catalog. Hamfests are the way to go.

Richard Hull
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Turret post standoffs  $5.00 for all of these at the April mini-fest here in Richmond.
Turret post standoffs $5.00 for all of these at the April mini-fest here in Richmond.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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