Re: Tek 464 - Confirmation on Z-Axis frequency response performance

Fabio Trevisan

Hi Raymond,
Thanks for the heads up. My thoughts after your comment.

On Mon, May 14, 2018 at 01:40 pm, Raymond Domp Frank wrote:
You may check adjustment 5 in "Display and Z-Axis Adjustment", Vol. 1 page
4-33 in my Service Manual. Adjustment won't interfere with 'scope calibration.
Yes, I've been there already.
In fact, the Z-Axis frequency compensation network (on my 464 at least) has none to very little effect on the rising edge, although it has a noticeable effect on the falling edge, to the point of presenting a distinct undershoot when I under compensate it.
From Lop Pol's answer, apparently his 468 has the same "poor" performance, but since he's the only fellow I remember having asked about this subject (on another topic some months ago), I was in the hopes that more 46x owners could corroborate if this is just normal to this design or if my 464 and Lop Pol's 468 only share a common defect.
And yet, although there's not a screaming difference on the waveform between the rising edge and the falling edge, indeed the falling edge is faster by - maybe - 20~30ns.
It seems that's why the freq. compensation has an effect there and almost none on the rising edge.
This morning I was looking at the output of my 7623A's Z-Axis amplifier and it definitely does a better job. Rising and falling edges are about the same, at around 55ns, and the freq. compensation trimmer has about the same effect on both edges.
It's difficult to assess if the problem is on the output stage or on the incoming signal because the input of this amplifier is current driven, but my guess is that this slow attack is already coming from the input signal.
I`ll try to confirm that inserting a low-value resistor in series with the emitter of Q1424, hoping not to trouble too much its operation (I don't have a current probe).

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