OC45

[Fox]

Hi Folks

I'm building a Rangemaster TB clone, and after trying various Ge trannies for tone and gain  I've decided on a Mullard OC45 orange spot. Its the only orange spot I've got out of a bang of mixed, however I am wondering if anyone knows the significance of the orange spot. There are also blue spots available but the difference is a mystery to me, all I know is that the OC45 is an IF tranny normally used in superhet radios, the orange is normally used before the blue in the circuit. If anyone can shed some light on the matter then I'd appreciate it.

cheers
Fox

[foxfire]

i remember reading somewhere that the dots were used to indicate transistors that test in a certain range. i'm guessing that with the wide HFE values found on old GE's it was just easier to use the colored dots as an additional way to categorize them. if i'm wrong i'm sure someone well pop in soon and correct me... rylan

[newfish]

I have some Mullard OC45s with a blue mark on them.

Initially I figured this was just a way of denoting which pin was the Emitter or whatever.

Now Rylan's explaination makes sense, as they're not that hot sounding in a Rangemaster.

They *do* make a good Fuzz face though...

If there's anyone else looking for Rm trannies, I can recommend 'CV 7003' - the Mil.spec OC44 I believe - they work... 

[Paul Perry (Frostwave)]

Just to complicate things, some transistors from then were coloured to indicate high frequency cutoff. You can get away with slightly lower freq for the IF stage (455KHz) than for the RF oscillator/mixer.
I expect that the OC45s referred to were graded by gain, though.

[George Giblet]

>Initially I figured this was just a way of denoting which pin was the Emitter or whatever.

Many old transistors use that method of marking. (Often red for pnp and blue for npn, I'm not aware of orange for rf pnp so I can only assume it's like red.)

[maartendh]

Hello,

just had a peek in my old book on building radio's which in the last chapter also gives some attention to this phenomenon which has in so many ways pushed tubes aside, as they state it. In this chapter following explanation of colors is given:
red dot: denotes the Collector
blue dot: emitter
white dot: base
Instead of marked by a red dot, the collector can be connected (and therefore recognized) to the metal case.

Maarten

[Fox]

ok, I've confused people here...the orange dot or blue dot are on the top off the black encasement, they also have the red collector dot. Its like a transistor wearing a coloured hat

cheers
Fox

[Fox]

I found out that orange spots have a higher gain than blue spots, what the criteria I dont know.

cheers
Fox