Help needed replacing an HP/Agilent 3312A P-channel JFET - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: October 14, 2013, 05:19:42 pm
content: Hola chaps,I have been hunting online without joy but basically, need help to find a replacement (or equivalent) P-channel, D-mode, silicon, JFET.Original HP part number 1855- 0082 (Mfr code 28480)The JFET I pulled, reads M5-082 636 (TO-92 chassis)I haven't even managed to find any specs, although the service manual states that the 'amplitude of the main generator can be adjusted between 0-20v p-p in an open circuit.' -There are two JFET's in the circuitry - One P- Channel (non-original TO-92), one N-Channel (original? TO-18)Can anyone please suggest a compatible P-Channel part number?Many thanks in advance.

author: dannyf
author_rank: Super Contributor
timestamp: October 14, 2013, 05:31:20 pm
content: You can probably help your cause by posting more information about the jfet, like what it does, where it is used, and schematic if possible.

author: JoeO
author_rank: Frequent Contributor
timestamp: October 14, 2013, 05:36:25 pm
content: This page lists it as a 2N4360.See if the specs fit your application.http://www.parttarget.com/5961-00-442-9470_5961004429470_1855-0082.html

author: Unknown
author_rank: Unknown
timestamp: October 14, 2013, 05:57:15 pm
content: Hi JoeO,Thanks for that,as we only have limited outlets here, I'll take that number and see if anyone has one.Danny,it is part of the HP 3312A Function Generator symmetry circuit.The schematic can be found here.http://circuitslab.case.edu/manuals/Hewlett_Packard_3312A_Function_Generator_Operating_and_Service_Manual.pdfPage 41, Schematic A1, component Q301 - (located just above the 'Modulation Symmetry Adjust' pot).

author: dannyf
author_rank: Super Contributor
timestamp: October 14, 2013, 06:20:55 pm
content: It looks like a switch (controlled by Q302?) that discharges the capacitors on the integrator. A j fet with small Rds should work.

author: Unknown
author_rank: Unknown
timestamp: October 15, 2013, 12:43:49 am
content: Well that was waste of several hours!Went into Rio and after 8 components shops, the only thing even remotely similar that I could find, was a 2N4342, which to be honest, gave a much clearer square wave, but totally trashed the sine and triangle waveforms.This is the problem with living in a Third-World country. Many basic products (components) just don't exist here.I know the drug-fueled politician criminals are telling everyone that Brazil is changed and ready to host the Olympics, World Cup and whatever, but the hard fact is that here in Rio, over half the State doesn't even have basic sanitation such as running water and sewers!And Rio is the wealthiest State in Brazil!!!!!So social problems aside.... if anyone has ANY kind of idea, as to a common P-Channel JFET which can be used in place of an HP 1855-0082....Please don't be shy.

author: Vgkid
author_rank: Super Contributor
timestamp: October 15, 2013, 02:29:02 am
content: NTE 326 looks to an equivalent. You can still buy the correct part from American microsemi.

author: Unknown
author_rank: Unknown
timestamp: October 15, 2013, 10:44:50 am
content: Hi Vgkid,Thanks for the suggestion.Did try to find an NTE 326 yesterday but without joy.Maybe I'll try Sao Paulo.The problem with buying from the US is the paranoid Postal controls - which means that anything, any size, takes over a month to arrive here!It's easier, quicker and more secure to buy from China. It's just a sad sign of the times!