Replace Component in Old Oscilloscope: Solutions Wanted

[Ravaner]

Hello. I have to replace a component at the input of an old oscilloscope. The reference is unfoundable ( 41R105 ? ) in fact it is 2 NFET transistors in the same package (TO-39). I guess Ft is >= 1 GHz. I'm just looking for a component of the same kind (of course not same reference) that iI can find with reasonable difficulties. Thanks by advance for ideas ...

 

[Enthalpy]

Why shouldn't you buy a small lot of single transistors and extract a matched pair through their Vth for instance?

Beware integrated circuits have been made in TO-39, including op amps and HF circuits.

 

[yungman]

I looked up some dual JFET in Digikey:

http://www.digikey.com/product-search/en/discrete-semiconductor-products/jfets-junction-field-effect/1377093?k=dual%20rf%20jfet

I don't know whether this is what you want.

If not, find a matching pair like Enthapy said, put them back to back with good surface contact, preferable put some heat sink goop between them and tie them together. This will give you good temperature tracking.

 

[Ravaner]

Thanks for your replies. That's probably what I'll do.

 

[Enthalpy]

Deeply buried memories...

Last time I considered using Jfet for HF, a good part was the 2N4416, and it's still available on eBay, both in TO72 AND TO92 which should ease a thermal contact between two parts.

I hope you speak sanskrit to read the datasheet, and have kept your tools of reindeer bones and flintstone.

At least a selection guide from National Semiconductor is there, where deepest layers aren't necessarily older:
http://www.alldatasheet.com/datasheet-pdf/pdf/50026/FAIRCHILD/J300.html
the J300 exists on eBay as well, the J300 and J310 being as fast as the 2N4416 with other Idss that may match your part better.

How did you know the component with obscure marking is a double Fet? Back then, the µA733 had a TO39 case as well, and this video amplifier would make sense in an oscilloscope.

 

[Ravaner]

Hello. Thanks for reply. I know pretty well 2N4416 I used in many HF boards ... I know that this is a double Fet because I own the schematics but unfortunately without any component commercial reference