Products > Test Equipment
Cloning the HP3325A Option 002 - HV Output
Tazz:
Quoting some 2015 post on group.io:
--- Quote ---pianovt
7/21/15 #70601
It looks like Bob saved the day! Just in case someone finds this thread in the future while searching for a replacement, here is what I found for the 1854-0475 dual NPN:
Vceo >40V
NF < 3dB
Ft > 15 MHz
Cob < 3pF
hfe > 200 at 100uA
hfe match better than 0.8
Vbe match better than 10mV at 100uA Ic and 5V Vce
Pd 750mW max. at Ta
Vladan
--- End quote ---
Cob is way to high on LM194 based clone in general. It is not specified on the AS version.
They are generally slow too, as the Hp one so with high Vce/Ic polarisation and high Pd : The Hp one even rated at 750mW is mounted with a dissipator.
Tazz:
2N2920AHR seems to be a good replacement. Active product but difficult to find (ST space qualified portfolio).
Microsemi 2N2920(L) is only 350mw max an very expensive.
2915A/2920A from Solid Sate Inc/Texas Instruments, 2N2920 from Thoshiba 2920A from central semi should be good but hard to find or obsolete.
Why not simply MAT01 ? Available anywhere at not foolish price. Ok perhaps a little but expensive for the HV option, but as a general 1854-0475 replacement ?
2920A From Solid State cost only 2$ less than a MAT01GHZ (~17 vs ~19)
Jay_Diddy_B:
--- Quote from: Tazz on May 17, 2020, 12:34:10 pm ---2N2920AHR seems to be a good replacement. Active product but difficult to find (ST space qualified portfolio).
Microsemi 2N2920(L) is only 350mw max an very expensive.
2915A/2920A from Solid Sate Inc/Texas Instruments, 2N2920 from Thoshiba 2920A from central semi should be good but hard to find or obsolete.
Why not simply MAT01 ? Available anywhere at not foolish price. Ok perhaps a little but expensive for the HV option, but as a general 1854-0475 replacement ?
2920A From Solid State cost only 2$ less than a MAT01GHZ (~17 vs ~19)
--- End quote ---
The circuit will work quite well with two ordinary MPS8099 transistors glued together.
When I built mine it worked fine, without selecting or matching the transistors.
In simulation a miss-match of HFE one transistor 250 and the other 300 results in about 20mV of offset on the output.
I would try ordinary transistors before going chasing after special parts.
Total Power dissipation for both transistors is around 180mW.
The HV Option 002 amplifier schematic is similar to the normal output. Look at the schematics in the service manual. I am guessing the dual transistor was copied from there. :-//
Regards,
Jay_Diddy_B
Tazz:
Yes going back in the thread show me that I should have reread all first instead of going through all reference catalogs ... :-DD
Jay_Diddy_B:
Tazz,
You can buy a *lot* of general purpose transistors for the price of the MAT01 or equivalent. You may even have some ;D
The transistor in the input stage have 45V VCE. (+/- 30V minus the 15V Zener)
So you need 60V parts.
I used 80V parts.
Jay_Diddy_B
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