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Anyone have a Tek 151-1076-01 or 151-1076-00 (WN537B?) JFET to fix a scope?
scopeman:
Hi Guys,
I am working on a Tek Telequipment D34 small portable analog scopes. There is a JFET, TR302 in the CRT circuit that is a Tek Part 151-1076-01 or a 151-1076-00 aka WN537B N Channel JFET
I can't find any data on this part or a replacement for it. I have tried 2N5457's and 2N5459's and they work well but only for a few hours. Being in an HV circuit it's hard to quantify what is going on other than perhaps breakdown. It seems that JFETS, especially higher voltage ones are rare these days.
I was thinking about putting some 20V or so zeners from the Gate to Source and from the Drain to source to protect the 2N5457 parts but am unsure of how that would affect the normal circuit operation of the current source circuit.
I have included a schematic of the HV Section showing the TR302 and a circuit description and a picture of a working one from the web.
So if anyone happens to have any of these parts I would appreciate getting one or two. The scope was made by Telequipment in England a subsidiary of Tek and overall is one of Telequipment's better efforts as it has a really sharp Tek ceramic bell tube and regulated power supplies (something the earlier Telequipment scopes were not known for).
Thanks for your time!
Sam
W3OHM
floobydust:
With 150V on the drain, limited or no offerings for high voltage JFETs or depletion mode MOSFETS. Pretty rare bird.
It does not look hand selected though and estimating the operating point, you can calculate gate voltage but drain current is a bit complicated.
You could hit up Sphere for the part and see what they could dig up, talk to the bank for financing.
Maybe consider LND150 VDS 500V, VGS(OFF) -1 to -3V, IDSS 1-3mA.
scopeman:
Wow thanks for that. Now if I can find someone that has the To-92 version of that LND150 I think I'll be set.
Sam
uski:
Unless you have a reason to go with TO92 beyond ease of installation/soldering (such as thermal dissipation), if I were you, I would order a few of the SOT23 version right now while it is still available : https://www.digikey.com/en/products/detail/microchip-technology/LND150K1-G/4902831
You should be able to install it with small wires. Or if you want to get fancy, a small PCB adapter.
PS: You can keep searching for a better option and replace it later on. But at least it secures a solution immediately. With the current chip shortage and factories pivoting away from certain exotic parts, I think your best bet is really to secure that solution while you can.
Fungus:
--- Quote from: uski on January 05, 2023, 08:04:24 am ---You should be able to install it with small wires. Or if you want to get fancy, a small PCB adapter.
--- End quote ---
Search on Aliexpress for "SOT23 TO TO92" gives this:
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