Early Mullard PNP Silicon Transistors - UK Vintage Radio Repair and Restoration Discussion Forum

Restoration73 · 18th Oct 2020, 11:14 am

In my stock I found a bag of 5 of these with a data sheet indicating they
are "for educational use". No markings on the metal case (like an OC81)
but the end is dipped in a purple lacquer. I also have some similar looking
BCZ11 (Mullard) and I am wondering if the internal construction is similar
to germanium devices of the period. Any info welcomed.

Refugee · 18th Oct 2020, 1:07 pm

Those will most likely be OC200 series. (OC20X).
I have got a few salvaged ones with either no markings or OC200 numbers.

Hartley118 · 18th Oct 2020, 3:18 pm

It's worth checking the forward votage of the base-emitter junction with a DMM on the 'diode' test setting. If 0.2 to 0.3 V, it's Germanium. If 0.6 to 0.7V it's silicon.

Martin

Restoration73 · 18th Oct 2020, 3:59 pm

They are Si, confused about the typed sheet stating Mullard, probably out of spec OC200. I also acquired some old bags of surplus transistors a few weeks back, "Bi-Pak" all work, some low hfe, no manufacturer or numbers marked on cases.

About 50 years back I made an amplifier using Ge devices, I remember the hiss on the
mic preamp. Replaced with pnp silicon, much less noise !

Jon_G4MDC · 18th Oct 2020, 4:07 pm

Bi Pak, at a couple of different addresses over the years in Baldock Street, Ware, Herts.
Their bits were typically unmarked exactly as you describe. Painful if you mix them up.

Maarten · 19th Oct 2020, 12:37 am

For educational use, likely points to production rejects. The datasheet should be similar to that of the corresponding 'normal' transistors but with some parameters wider or lower.

emeritus · 19th Oct 2020, 10:53 am

When I was at college in the second half of the 1960's the electronics lab had a supply of both small signal and power transistors for us to use that were completely unmarked. Presumably manufacturers' out of spec devices, but I never saw how they were packaged or knew who made them.

kalee20 · 20th Oct 2020, 6:30 pm

If they're OC200 series, they can be useful!

Normal silicon planar transistors can't take more than 5V reverse base-emitter. But the OC200 - from memory - is good for 15V or more. Useful for multivibrators or anything where reverse bias happens!

G6Tanuki · 20th Oct 2020, 7:25 pm

I've used loads of OC200-series in the past for DC switching, audio-amplification and the like. They were Mullard's cheap-and-cheerful silicons, working up to a few MHz - the Silicon equivalent of OC44/45/70/71/72/75/81.

Back then there was a 'thing' for symmetrical-transistors, where you could interchange emitter and collector and things would still work; entire telephone-exchanges were built around such stuff, where a "beta" of better-than-30 meant it was acceptable [Texas Instruments, and your BCY3x range, I'm looking at you!]

Ed_Dinning · 20th Oct 2020, 8:18 pm

Yes, the later and more modern looking Mullard BCY30 series, were a symmetrical transistor and used in industry as a replacement for OC200 types.
This allowed them to be used as an SCR facsimile, very useful in timers.

Ed

18th Oct 2020, 11:14 am	#1
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Early Mullard PNP Silicon Transistors In my stock I found a bag of 5 of these with a data sheet indicating they are "for educational use". No markings on the metal case (like an OC81) but the end is dipped in a purple lacquer. I also have some similar looking BCZ11 (Mullard) and I am wondering if the internal construction is similar to germanium devices of the period. Any info welcomed.

18th Oct 2020, 1:07 pm	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Early Mullard PNP Silicon Transistors Those will most likely be OC200 series. (OC20X). I have got a few salvaged ones with either no markings or OC200 numbers. Attached Thumbnails

18th Oct 2020, 3:18 pm	#3
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	Re: Early Mullard PNP Silicon Transistors It's worth checking the forward votage of the base-emitter junction with a DMM on the 'diode' test setting. If 0.2 to 0.3 V, it's Germanium. If 0.6 to 0.7V it's silicon. Martin __________________ BVWS Member

18th Oct 2020, 3:59 pm	#4
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Early Mullard PNP Silicon Transistors They are Si, confused about the typed sheet stating Mullard, probably out of spec OC200. I also acquired some old bags of surplus transistors a few weeks back, "Bi-Pak" all work, some low hfe, no manufacturer or numbers marked on cases. About 50 years back I made an amplifier using Ge devices, I remember the hiss on the mic preamp. Replaced with pnp silicon, much less noise !

18th Oct 2020, 4:07 pm	#5
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Early Mullard PNP Silicon Transistors Bi Pak, at a couple of different addresses over the years in Baldock Street, Ware, Herts. Their bits were typically unmarked exactly as you describe. Painful if you mix them up.

19th Oct 2020, 12:37 am	#6
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Early Mullard PNP Silicon Transistors For educational use, likely points to production rejects. The datasheet should be similar to that of the corresponding 'normal' transistors but with some parameters wider or lower.

19th Oct 2020, 10:53 am	#7
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,337	Re: Early Mullard PNP Silicon Transistors When I was at college in the second half of the 1960's the electronics lab had a supply of both small signal and power transistors for us to use that were completely unmarked. Presumably manufacturers' out of spec devices, but I never saw how they were packaged or knew who made them.

20th Oct 2020, 6:30 pm	#8
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Early Mullard PNP Silicon Transistors If they're OC200 series, they can be useful! Normal silicon planar transistors can't take more than 5V reverse base-emitter. But the OC200 - from memory - is good for 15V or more. Useful for multivibrators or anything where reverse bias happens!

20th Oct 2020, 7:25 pm	#9
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: Early Mullard PNP Silicon Transistors I've used loads of OC200-series in the past for DC switching, audio-amplification and the like. They were Mullard's cheap-and-cheerful silicons, working up to a few MHz - the Silicon equivalent of OC44/45/70/71/72/75/81. Back then there was a 'thing' for symmetrical-transistors, where you could interchange emitter and collector and things would still work; entire telephone-exchanges were built around such stuff, where a "beta" of better-than-30 meant it was acceptable [Texas Instruments, and your BCY3x range, I'm looking at you!]

20th Oct 2020, 8:18 pm	#10
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Early Mullard PNP Silicon Transistors Yes, the later and more modern looking Mullard BCY30 series, were a symmetrical transistor and used in industry as a replacement for OC200 types. This allowed them to be used as an SCR facsimile, very useful in timers. Ed