Search found 1317 matches

by John Futter
Wed Apr 07, 2021 8:31 am
Forum: Neutrons, Radiation, and Detection (& FAQs)
Topic: Channeltron woes
Replies: 18
Views: 1220

Re: Channeltron woes

ChristofferBraestrup your included circuits provided all the clues the VT 120A preamp is fed via a 10pf cap so for about 100kHz pulse repetition this equals about 3 meg input impedance into the 50 ohm preamp. Yes your preamp is 50 ohms optimized for extremely low noise current input and with a gain ...
by John Futter
Tue Apr 06, 2021 9:30 am
Forum: Neutrons, Radiation, and Detection (& FAQs)
Topic: Channeltron woes
Replies: 18
Views: 1220

Re: Channeltron woes

Again
an input impedance of 50 ohms is going to attenuate your signal by 20,000 times if it has a source impedance of 1 megohm.
so .2volts out multiplied by 20000 gives 4000 volts coming from your channeltron (I do not think so)
by John Futter
Mon Apr 05, 2021 7:12 pm
Forum: Neutrons, Radiation, and Detection (& FAQs)
Topic: Channeltron woes
Replies: 18
Views: 1220

Re: Channeltron woes

1 meg is very low and that is your source impedance so terminating the scope to 50 ohms will be a very big attenuator I would use 10 meg or higher and then use a preamp in your metal box as an impedance convertor ie Jfet frontend and 50 ohm output impedance so you can use the scope termination. This...
by John Futter
Mon Mar 15, 2021 5:56 pm
Forum: Neutrons, Radiation, and Detection (& FAQs)
Topic: TC 535P Timer/Multi-Scaler NIM issue - Help is needed
Replies: 7
Views: 480

Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

THX Arthur Nearly all breakdowns of these modules are due to failing tantalum capacitors that decouple the supply lines to the ic's usually they have the series resistor ( especially so in the ORTEC modules) check all caps carefully for discoloration they go so short circuit that they do not necessa...
by John Futter
Mon Mar 15, 2021 5:43 pm
Forum: Neutrons, Radiation, and Detection (& FAQs)
Topic: TC 535P Timer/Multi-Scaler NIM issue - Help is needed
Replies: 7
Views: 480

Re: TC 535P Timer/Multi-Scaler NIM issue - Help is needed

Arthur
Hoiw about following the rules you signed up for when joining this site
1./real full name not just your first name
2./ first post to be in the "please introduce yourself" forum


please amend
by John Futter
Mon Mar 01, 2021 5:52 pm
Forum: Vacuum Technology (& FAQs)
Topic: Pirani gauge vs plasma
Replies: 5
Views: 563

Re: Pirani gauge vs plasma

Maciek
It is important that the pirani cannot see the plasma.
active ions arriving will cause heat. The actual exposed thermocouple is extremely small with very low heat capacity.
a couple of righthand bends to isolate the Pirani from the main chamber should sort it
by John Futter
Mon Mar 01, 2021 4:18 am
Forum: Vacuum Technology (& FAQs)
Topic: Help me in my baby steps in the vacuum world.
Replies: 17
Views: 1882

Re: Help me in my baby steps in the vacuum world.

Richard
When we were using Fris grid detectors at work (these are fancy Geiger tubes that position detect) we used Argon and a little 1-2% propane by volume as the quench agent
by John Futter
Mon Feb 15, 2021 1:36 am
Forum: Images du Jour
Topic: House move and cleanup continues
Replies: 2
Views: 409

Re: House move and cleanup continues

Richard
you are bang on
All of those were 2mA max
the 100kV negative I was tempted to keep but!!!
by John Futter
Sun Feb 14, 2021 7:22 pm
Forum: Images du Jour
Topic: House move and cleanup continues
Replies: 2
Views: 409

House move and cleanup continues

We are having a new house built around 100 kms away from where we normally live and a lifetime (almost) of accumulated junk has to go.
So another trailer load to the tip yesterday all very sad!!
spellmans.jpg
by John Futter
Fri Feb 12, 2021 6:16 pm
Forum: Vacuum Technology (& FAQs)
Topic: DIY Turbopump Controller
Replies: 31
Views: 4320

Re: DIY Turbopump Controller

Nicolas It is hard to use linear optos to get volt and current sense across I make sure that there is series impedance then 5 volt TVS diodes across micro I/O pins my comments were directed at some of the other posts where micro derived drive signals are use to drive the half bridge directly a TMP 5...