2SC73 equivalent

[newlite4]

Anyone know a good equivalent for this NPN germanium transistor. It is the frequency converter in a Sony TR-7120 circa 1959. The original checks out OK on a Peak analyser at hfe of 200 but I suspect some deterioration when using a go/nogo led type tester.
Neil

[Herald1360]

2SC173 and 2SC178 come up as possibles, but they're probably no easier to find.

Unless the device isn't working as expected, I wouldn't replace it. Remember Ge devices can look pretty awful leakage wise compared with silicon even though they're fine.

Otherwise try any old silicon npn device- BC547 etc etc. Maybe need a tweak to the biassing..... drop the emitter resistor to about 1K from the 3.3k fitted.

[newlite4]

Thanks for the equivs, it looked as though this device had been removed before, it does appear to be leaky.
Neil

[Anthony Thomas]

My Towers International transistor selector (3rd update) suggests BC107 and A157 though I realise that the BC107 is not a Germanium type.

My Babani "second book of equivalents" suggests 2N168A-1086 and 2T73R. of these only the 2N168A seems to be a Germanium type. 2N1068 is a silicone type apparantly.

Checking the hfe listed for some of these transistors shows the 2SC73 as having a hfe of approximately 50. I wonder how accurate this data is?

Hope someone else can come with better suggestions, I do not have many Germainium transistor in my spares collection.

[newlite4]

Nice one Anthony, I nipped home lunchtime and fitted a BC107 in the frequency converter position and it fired up first time with room filling sound! It appears that the original suspect 2SC73 had been refitted incorrectly (C-E E-C) in an attempt to fix the original fault that I cleared last night - shorted tuning cap vanes.
Thanks all,
Neil

[Anthony Thomas]

Originally Posted by newlite4

Nice one Anthony, I nipped home lunchtime and fitted a BC107 in the frequency converter position and it fired up first time with room filling sound! It appears that the original suspect 2SC73 had been refitted incorrectly (C-E E-C) in an attempt to fix the original fault that I cleared last night - shorted tuning cap vanes.
Thanks all,
Neil

All's well that ends well Neil!

I wonder how many times attempts at repairs have totally backfired?

Quite often the collector is well marked on transistors either by a colour spot, spacing away from the base and emitter or other means. I always make small drawings of how things are before I strip down the set for changing of a faulty part, it is not allways the replacement part is identicle in configuration.

Tony

[don200002]

I wonder if the original would sill work if refitted in the correct orientation, especially now you have found the original fault, some of those germanium transistors were quite hardy.
Don,

[newlite4]

Hello Don, no, I did try that and the mixer-oscillator stage would not oscillate. Although it checked out OK on the Peak analyser, there was some reverse leakage visible when tested on the LED type tester. I can only suspect that the combination of age and a period of reverse biasing had taken their toll. These repairs can certainly be made more complex when someone else has been in there first and "had a go".
Neil

[don200002]

Hi Neil,
I agree, during my time in the workshop many an hour was wasted due to the "phantom knob twiddler" but I suppose we all have to learn somewhere, in fact, just by reading the posts in this forum I tend to learn something new every day.
Well done with the repair.
Don.

[jonnybear]

When I was working in the trade, we used to call them Thrombosis Finger, (clot with finger trouble), Two germanium NPN replacements according to Towers update 5 is asy28, 2N1306 if that helps.

[westcliff]

The information I found states that 2SC73 can be replaced by ASY28, 2N1304 and GT122A.

Gus.