HP9100 EHT oscillator transistor

From: Geoff Roberts <geoffrob_at_stmarks.pp.catholic.edu.au>
Date: Mon Dec 21 23:40:30 1998

-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
Date: Tuesday, 22 December 1998 15:24
Subject: Re: HP9100 EHT oscillator transistor

>If it is a 2N1701, then the maximum collector current for that device is
>2.5A. The transistor is part of a blocking oscillator using the EHT
>transformer, the supply to which is fused at 750mA. But the maximum
>collector current for a BF259 is only 100mA. I am suprised it worked at
>all, but work it did.

It will be a short life I suspect. It's probably drawing around 200ma.

>The maximum voltage is not a problem. The oscillator runs off an
>unregulated 20V line, and there are no HV spikes flying around. The
>2N1701 is only rated at 60-odd volts, which the BF259 (or any of the
>other transistors I've tried) can stand trivially.

Well, a 2SD350 or 380 are fairly common HOP transistors, they will certainly
run at line freq, I don't have a data book handy, but they have Ic ratings
of well over an amp. 2N3055 might work too, though I'm not certain it could
handle the frequency. They all have TO3 cases though, so mounting it might
be a headache.

If I can dig up a data book in this mess I'll see what else I can come up


Geoff Roberts
Computer Systems Manager
Saint Marks College
Port Pirie South Australia.
My ICQ# is 1970476
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Received on Mon Dec 21 1998 - 23:40:30 GMT

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