Re: Resistor in series

Stephen Hanselman


I saw similar things when I was working on Silicon Valley 700W FM amplifiers. The physical orientation of the ATC caps was critical. We noted that sometimes two or three caps needed to be placed on edge or even stacked on top of each other.

RF is always fun but this added a new twist.


Stephen Hanselman
Datagate Systems, LLC

On Nov 27, 2020, at 14:50, Dennis Tillman W7pF <> wrote:

´╗┐There is another explanation for doing something like this which is not as obvious.
If you look at the schematic for the 067-0681-01 Tunnel Diode Pulse Generator designed by John Addis at Tektronix

There are three 1/8W 1Kohm resistors (R4, R5, and R6) connected in series going to the tunnel diode. Several years ago I asked him why he did not use one 3Kohm resistor instead. What he knew and I learned was that the body capacitance of each of these 3 resistors in series was far less than the body capacitance of one 3Kohm resistor. The TD is being driven by the collector of the transistor which is high impedance, and the three 1Kohm resistors in series reduces the time constant of the pulse going to the Tunnel Diode without adding any additional capacitance across the Tunnel Diode that would slow it down.

I doubt this had anything to do with Tek portable scopes since their frequency response is almost two orders of magnitude slower than the fast edge of the Tunnel Diode Pulse Generator but sometimes there are other explanations for why you might encounter things that are not obvious.

Dennis Tillman W7pF

-----Original Message-----
From: [] On Behalf Of Milan Trcka
Sent: Tuesday, November 24, 2020 9:09 PM
Subject: Re: [TekScopes] Resistor in series

Jeff, the resistors connected end to end are an attempt to make a required resistance that was not available as a standard resistor value. Shortage of parts? Engineering change? Select in test? Who knows. I have a few of those in my 453 scope.

Dennis Tillman W7pF
TekScopes Moderator

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