need N-JFET data sheet

Hello John,

That sounds like an internal HP part number. They had many of their transistors custom made or at least custom labeled. Often they can be substituted but without that part of the schematic it is hard to see which one could be used instead. An audio oscillator doesn't seem too challenging in terms of capacitances etc.

I don't have a cross for that HP part, but here are some HP numbers I've compiled:

What's the model number of the signal generator?

Hello Michael,

Indeed they do. Thanks! Got it bookmarked, for the day when something goes poof in the lab and it's out of support.

If you have any that aren't listed, please send them to me. A 300 DPI GIF is preferred, so I can use my scan to text software to do most of the work.

BTW, if you right click and save the HTML file to your hard drive, you won't lose it if something happens to take me back off line.

Hello Walter,

Can't be the one they built in that famous HP garage.

My problem is a little tougher. Ye olde Rohde&Schwarz SMF generator has decided that 50 years is enough. I loved it for its low noise, not rivaled by any of the modern gear here in the lab. The cathode current of the oscillator tube faints after a few minutes of operation. Unfortunately that old EBF11 steel tube is unobtanium unless one is willing to pay collectors prices. John can probably substitute another JFET here but that tube is another matter :-(

Jeorg, check ALL of the coupling and bypass capacitors for leakage. I have a TS-382 military audio generator of that vintage, and every paper capacitor in it is defective, including the oil filled "Bathtub" capacitors soldered into sealed cans. Mine is so bad that it doesn't even get to warm up before one of the grids goes positive, and burns up three 10 Kohm, 1 W resistors in the screen circuit of the driver stage. I am restuffing the cans with metalized polyester capacitors that I bought from

Hello Michael,

Thanks for the hint. Although a grid going positive should lead to more cathode current. In the SMF case it just drops off. Looks like the cathode is just plain tired. But I'll go in there and measure again.