Re: Infamous D180 is it good or bad.


Eric
 

Hey Albert,

    I got the waveform measurements taken. I am thinking they look pretty good but I might be missing something. Photo is here this was taken unloaded the TD assembly was not even installed.

https://groups.io/g/TekScopes/album?id=248421

Eric

On 6/9/2020 6:25 AM, Albert Otten wrote:
Hi Eric,

A few messages ago I wrote that a drift in R184B+C has far less effect than a drift in R180. That's correct when Pulse Out is not loaded. I forgot that In normal use Pulse Out is loaded by 50R and then the situation is nearly symmetrically.
I did some TD current calculations based on nominal values, 50R load, and assuming 5R TD resistance, +/- 15V inputs, and then changed R184B+C to your 723R.
Nominal, 660R: 20.35 mA.
Your 723R: 19.39 mA.

Even with the TD tube removed you might probe the voltage wave forms at the base of Q135 and Q145. Assuming 0.7 V base-emitter drops that gives you a (slightly optimistic, ignoring base current) check of the input voltages to TD circuit.

Albert

On Mon, Jun 8, 2020 at 11:31 PM, Eric wrote:

Well given that the TD is good That means that the 284 has a bias or
connection issue. I pulled apart the assembly and I have and R180
measures at 746.1 close enough for me for a spec of 750. However R 184 B
+ C measure 723 Ohms when I expect 660, R184 A was not involved in the
measurement as the resister was removed from the air line at the time of
measure so the 50 Ohm R184A was open on one side.

But a 15V pulse in to 746 Ohms would lead to 20.11mA of current in to
the front of the TD unless I am missing something?

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