Re: Type 284 TD Bias issues


I am reviving a long dead thread to say thanks for the help on this repair. I was able to get the 284 back to working 100%. The TD was good and this was a biasing issue with the resisters. If any one else has this issue 1206 surface mount resisters will fit inside the 54 Ohm back terminator and can easily be used you will need to form a lead on one sided to get the leg to terminate at the back of the air line but this actually helps a little as lead inductance is reduced. I cannot say how much of an effect this has cause my gear doesn’t go that fast.


-----Original Message-----
From: <> On Behalf Of Eric via
Sent: Sunday, February 28, 2021 1:59 PM
Subject: [TekScopes] Type 284 TD Bias issues

I have a type 284 that I am working on again to see if I can’t get the td pulse side working again. Where I am at now is the last time I was in the pulser I was able to confirm that D180 is good on a curve tracer. My issue seems to be in R184 B&C. R180 seems to be good as well as R184A R184 B&C is a 2 carbon comp series resistance that should be 660 Ohms mine measure 724 Ohms if my understanding of the circuit is correct the 2 resister combination was done due to size constraints along with parasite capacitance reduction. They are carbon 1/8 Watt resisters. The challenging part is they need to be inside R184 so space is extremely critical. I can get resisters from NTE that look like they might fit. Is there any reason that I can not play with the resistance values as long as the sum total is 660 Ohms? Also given that there are IN the tunnel diode air line is resister material an important consideration given the 70 Ps rise time of the TD. In circuit this is the negative bias driver for the TD. On the positive side of things R180 is reading 749.82 Ohms so that does not need to be changed.


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