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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 30th Jul 2021, 8:54 pm   #1
Goldieoldie
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Default OC45 transistor.

Hi all
We all know about the issues with AF117 series of transistors.
I’ve always regarded the OC series to be ultra reliable ,until today !
Had a Philips radio with low gain.After the usual checks I found the 1st IF OC45 was low gain .
I’ve never in all the years of repairing radios had an OC45 fail.
Have others found the same ?
Cheers
Pete
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Old 30th Jul 2021, 9:01 pm   #2
G6Tanuki
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Default Re: Oc45

All parts have a propensity to fail; your OC45 could be 60 years old...

Legend has it that the OC44/45/71 transistors came off the same production-line but were then tested/graded for Hfe and Ft and got marked-up accordingly.

I've come across quite a few OC71 which - over six decades or so - have developed low-gain/fizzly-noises-at-AF.
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Old 30th Jul 2021, 9:27 pm   #3
kalee20
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Default Re: Oc45

Quote:
Originally Posted by G6Tanuki View Post
Legend has it that the OC44/45/71 transistors came off the same production-line but were then tested/graded for Hfe and Ft and got marked-up accordingly
OC44 and 45 probably were the same, the 45 is the lower-spec for ft. But I remember reading in a Mullard Outlook that the OC71 used a rectangular piece of germanium and the OC44 a circular, so it certainly wasn't the case that all three came from the same production process.
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Old 31st Jul 2021, 9:02 am   #4
Goldieoldie
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Default Re: OC45 transistor.

Yes I have had several OC71 go noisy.
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Old 31st Jul 2021, 9:48 am   #5
barrymagrec
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Default Re: OC45 transistor.

From memory OC41 / 42 / 44 / 45 were selected versions of the same transistor but entirely different to OC70 / 71 / 72 / OCP71 which again were all selected versions of the same device.

I think Mullard really only made two types of Germanium PNP signal transistor at the time but selected them into a complete range.
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Old 31st Jul 2021, 11:22 am   #6
kalee20
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Default Re: OC45 transistor.

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Originally Posted by barrymagrec View Post
I think Mullard really only made two types of Germanium PNP signal transistor at the time but selected them into a complete range.
Well... you could say that, but arguably you could also say that if process controls were better they would only need to market TWO transistors, the OC99 (with breakdown voltage of 30V, ft of 10MHz, gain of 100, and noise figure 3db; and the OC100 with gain of 100, breakdown of 40V, leakage 50uA, noise of 4db, and power dissipation of 0.3W.

The fact that they couldn't (at least at first) get the transistors to pass all the specs together meant that they really did have to grade them into the various numbers. Later on, it's possible that they did get the hang of making the super-chip which did the lot, and they just labelled them according to what orders they had. It would be interesting, for instance, if anyone has an OC45 which meets the OC44 specs.

Of course, the OC72 is an OC71 but in a package with metal sleeve, for better dissipation in output stages.
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Old 31st Jul 2021, 1:02 pm   #7
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Default Re: OC45 transistor.

Remember it was new technology then and rather pushing the limits of frequency capability.
No wonder they selected them it made for a more affordable line up, one 0C44 for the oscillator/mixer (about 2MHz needed) and the 0C45 for IF where gain at 450kHz or so was needed. Just take a look at the specs. for modern transistors and you will see a huge spread about the same as the whole 0Cxx series. Bit it doesn't matter now as they are used well within the limits.
 
Old 31st Jul 2021, 1:05 pm   #8
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Default Re: OC45 transistor.

...and it is 0 (a zero for zero heater volts) and C (triode) fits nicely into the valve numbering.
 
Old 31st Jul 2021, 3:01 pm   #9
kalee20
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Default Re: OC45 transistor.

Actually, it's not!

OC45 not 0C45. See the front cover, and the contents list, of my Mullard Quick Reference Guide, 1978, showing the OC series among the O's, not among the 0's. They're the folks who after all, made and labelled the things, they know what they called them!

(The opposite, of course, is apt to happen with the 1N4003, 1N941 etc, how many times do we see/hear this referred to as IN-whatever?)
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Old 31st Jul 2021, 10:11 pm   #10
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Default Re: OC45 transistor.

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Originally Posted by merlinmaxwell View Post
...and it is 0 (a zero for zero heater volts) and C (triode) fits nicely into the valve numbering.
Valve heaters always started with a letter in Europe, so that wouldn't fit at all.

Philips and a few other European manufacturers adapted the way they numbered valves for semiconductors and started using the O for two purposes: for cold cathode valves and also for semiconoductors.

While Pro Electron created a new numbering scheme using A..C for the band gap voltage of semiconductors, Philips continued with the letter O for internal use only.
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