Re: [AMMRL] P31 issues on Varian ,MR400

I concur with Mike - we need more input:

- in which way exactly does X tuning fail?

- does P31 tuning fail as well after X spectra?

- Bad matching on all nuclei? 

- Tuning resonance moves away after being OK initially?

- Increased noise during tuning?

- do you observe any arcing? Maybe run a dummy array of 100 or 1000 1-scan P31 spectra, maybe followed by tuning and 100 C13 spectra

Normally RF amplifiers don’t really get much extra heating from pulsing (short 10us pulses every few seconds represents near to no load at all).

Best regards 

Bert



Hi Ken,

“Tuning of all X band nuclei begins to fail” is not clear enough—does the tuning move off resonance or are you unable to tune the probe for some other reason?�= � One possibility is that the 31P experiments may be causing your coil (or some other component in the probe) to heat for some reason, which would affect all the X nuclei, and if it warmed up enough and started warming up the 1H coil, could cause it to detune as well. 

 

And after you turn it off for a while things cool back down and go back to normal (I assume you see the same if you just don’t pulse for a while?)  Anyway, that seems like a possibility to me.

 

Cheers,

Mike

 

From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of Sham, Shing
Sent: Thursday, September 14, 2023 8:04 AM
To: main_at_ammrl.groups.io
Subject: Re: [AMMRL] P31 issues on Varian ,MR400

 

Hi Ken,

If the problem is coming from the x-band amplifier, should it affect the C-13 as well?

 

Just my 2 cents. Good luck.

 

Simon

 

From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of Kenneth Sharp-Knott via groups.io
Sent: Thursday, September 14, 2023 8:56 AM
To: ammrl_at_groups.io
Subject: [AMMRL] P31 issues on Varian ,MR400

 

Hello Spinlandians,

 

I have a weird issue that I've been observing for years.

 

On my Varian MR400 of several P31 experiments are run in close sequence, the tuning of all X band nuclei begins to fail.  In fact it also begins to affect the tuning of the proton channel to a lesser degree. It also obviously impacts the sensitivity of those experiments drastically. My suspicion is that the lowband amplifier begins to overheat.  

 

Our solution has been to not allow P31 on this instrument as C13 doesn't cause this problem. For various reasons, I would like to figure this out so that P31 is again available.

 

I'm doing some troubleshooting, but I think it begins to recover after being off for a while.  It might also be the synthesizer.

 

What is weird is that this consistently happens after running a series of P31 experiments.

 

Any thoughts on this?

 

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