Canberra 814 / Ortec 4890
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Canberra 814 / Ortec 4890
Both of these NIMs are combination preamp/amp/disc and use BJTs for the charge sensitive preamp. The specs indicate that these have poor mV/coulomb gain factors (3.3mV/C) compared with JFET based preamps (200mV/C). I'm wondering if anyone is certain about the vulnerability of the BJT based preamp to rapid changes in bias voltage. I know that JFET based preamps can be damaged by sudden application or removal of bias voltage but my general inclination is that a BJT would be more robust. I want to use a 814 or 4890 with a fixed HV supply that only has on/off control but of course don't want to damage the NIM. Thoughts?
- Garrett
- Garrett Young
- Posts: 123
- Joined: Fri May 26, 2006 9:51 pm
- Real name: Garrett Young
Re: Canberra 814 / Ortec 4890
Update:
The Ortec 4890 has steering diodes on the input that should protect the BJT from sudden application/removal of voltage. Probably not best practice to abruptly change the bias voltage but it's nice to know some protection is present. I might add low leakage diodes (FJH1100) to my JFET preamp once I discover the root cause of the repeated failure.
The Ortec 4890 has steering diodes on the input that should protect the BJT from sudden application/removal of voltage. Probably not best practice to abruptly change the bias voltage but it's nice to know some protection is present. I might add low leakage diodes (FJH1100) to my JFET preamp once I discover the root cause of the repeated failure.
- Garrett