Hi Albert,
I tested your suggested setup and it does indeed have a positive effect. With a 7B53A in the B slot and set up to display a delayed trace, if I turn the B INTENSITY pot fully CW and then adjust the main INTENSITY control to see the trace without any observable highlighting. I can then rotate the B INTENSITY pot slowly CCW, I can start seeing the dual intensities and the highlighted one is not excessively bright. I can then make slight adjustments to both pots to where a clean, dual-intensity trace is displayed.
Is this the way the two INTENSITY controls should be used? I have been setting the A/B INTENSITY pots such that with the main INTENSITY pot at about 12:00 to 1:00 o'clock, the "basic" trace is visible and it was then if I elected to display a highlighted, delayed trace, I would see the excessively bright part of the trace. Perhaps this is merely operator error?
Thanks!
Barry - N4BUQ
toggle quoted message
Show quoted text
----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, November 19, 2021 8:11:48 AM
Subject: Re: [TekScopes] 7704A - Grid Bias
Hi Barry,
A month ago this was the "complaint" in your starting message of this topic:
If a any of my time bases are set to display a highlighted trace, the trace is
very much too bright. If I'm understanding this function correctly, the
plugins are setting a voltage on the AUX Z AXIS line. If this were one or two
plugins, I'd suspect the signal being set on AUX Z-AXIS being incorrect, but
since this is occurring on all of them, I suspect something is misadjusted in
the CRT circuit of the 7704A.
I suppose you used a dual time base like 7B53A in the A slot, though my same
remarks hold just as well for the 8B55/7B80 combo.
In both 7704As I tested with 7B53A the brightness contrast is *extremely*
influenced by the A INTEN setting. With A INTEN at maximum there is hardly a
visible contrast. But with just a slight amount below maximum the unintensified
portion vanishes. It's difficult to find a compromise. With 7B85/7B80 this goes
somewhat better.
In the fully CW position the wiper of the INTEN pot should make contact with
-15V. The pot is very well accessible if you remove the upper-right cabinet
panel. Maybe you have to exercise the pot a few times.
In my 7B53A the active intensifying voltage at TP620 is about -0.95 V.
[BTW Here is the simplified reason why A INTEN is so important for the contrast,
in stead of INTENSITY. In the Z-axis logic IC U2587<3> the effects of A INTEN
and Aux Z-axis are summed. The result (sink current) goes as Z-axis Signal to
the Z-axis board<14>. There the INTENSITY setting determines which fraction of
the Z-axis Signal passes via Q4175 (and really sets the CRT intensity) and
which remaining fraction passes via Q4163 (and gets lost). So INTENSITY effect
is not additive there to the A INTEN component but multiplicative to both
components].
