I once had an RM35 with double-peaking. The beam stayed focused across the initial peak and dip, and only broadened when I cranked Intensity to max.
YMMV,
Dave Wise
________________________________________
From:
[email protected] <
[email protected]> on behalf of Albert Otten <aodiversen@...>
Sent: Thursday, February 21, 2019 1:48 PM
To:
[email protected]Subject: Re: [TekScopes] Mechanism of CRT Double Peaking
On Thu, Feb 21, 2019 at 07:45 PM, Fabio Trevisan wrote:
Hello Albert,
I don't see the rationale behind this. With rising grid voltage larger rings
on the cathode disk take part in the cathode current. Moreover, the increasing
electric field strength in space just outside the already exposed smaller
rings makes it easier for electrons there to escape from the cathode. So I
would still expect a monotonically increasing intensity (or better, cathode
current).
Yep, as I mentioned... my rational may be (and probably is) flawed.
Back when I was still struggling with that 464 and romancing the chance there
could be some level of recovery to that CRT, I read a lot of things in a lot
of places... In many of them I encountered widespread use of the term "Double
Peaking" but in none of them I found explanation about the mechanism that
originates the behavior.
I agree that by my own rational, the intensity should always increase (maybe
not at an even, or linear fashion, but always increase).
Hi Fabio,
I searched around here and via Google and must say that nearly always cathode degradation is mentioned as the cause of double peaking. I hink now the explanation could be as follows.
The phenomena you describe lead to a quick increase of aperture when intensity is increased. Then the beam gets de-focused and that might produce a decreasing brightness for the observer, despite a monotonically increasing beam current. As soon as the aperture is at its maximum, the brightness might start to increase again.
Albert
