This topic is part of a project for a built in modulation scope going into the old Tucker transmitter, this is what I recently cut the 5" hole in a front panel for, etc. The scope is to be a high performance item, unlike cheap modulation scopes and old bench scopes hacked for the purpose (no offense intended).
Here is a detailed explanation of exactly what I am trying to do:
Please refer to the attached schematic.
I need fixed, accurate voltage drops of 50-500V. Devices can be put in series. They must operate on as little as 0.1mA and handle as much as 0.3 to 1mA. The exact voltage is not as important as stability over time, say 5000 operating hours. I can build up voltage drops if necessary from devices that drop 50-70V when conducting.
The DC current available from the section of the power supply that must be divided and regulated (-1450 to +500 section) is 2mA. This is divided between two voltage dividers so an upper limit of 1mA per each (in reality one will consume about 2/3 and the other 1/3 of whatever current is permitted). That is plenty as even the CRT anode consumes only about 100-200uA max. But there is a 2mA limit imposed by a reasonable size power supply.
The voltage divider current is expected to be stable, so the voltage drops across any neon lamps should also be fairly stable.
Increasing the CRT brilliance will not increase voltage divider current appreciably as the main load is from cathode to anode of the tube, with the intervening elements consuming only a few uA.
The attachment explains what I am trying to do with the neons, GV3A'a or whatever devices. I do not mind obsolete devices if I can buy a handful of spares cheaply.
The attachment shows Zener diodes as a placeholder device representing appropriate voltage drops.
I would like to use neon lamps or other non-solid state devices because the transmitter is made with late 1940's tech and I wish to keep it time-appropriate if possible.
Voltage regulating elements of some kind are important for this CRT. Not all of them have been shown in the schematic yet and it is subject to changes.
Even though cheap scope CRTs can be operated from almost haphazard voltages, There are many complex reasons for regulating and proportioning the various voltages for this CRT.
In short it will take better advantage of this high performance CRT and give me a set and forget display assuming RF and AF signals delivered to the deflection plates are repeatable. It will be similar to a Tektronix 545 oscilloscope in that the beam will be where you left it last week and when it is on it will be bright and sharp enough to see clearly across a well lit room.
That CRT is much more than a typical 5ADP1 or the like, primarily in the focus and brightness departments, as well as deflection accuracy and robustness against quick burns at high intensities. The acceleration voltage is 10KV on this one as opposed to about 4-6KV in many consumer grade scopes and 1-3KV in many modulation monitors.
I would have used a newer CRT like that in a 7904 mainframe but I had two NOS 545A tubes so there is the one and the spare.
please note the circuit is not completely analyzed so some voltages and resistances will be wrong, except the voltages marked around the CRT which are the target voltages.
I can answer in more detail about this mod scope project, and other aspects of it have kindly been addressed by valuable advice in other topics.
http://amfone.net/Amforum/index.php?topic=30071.0 (high level RF pick-off points to low-capacitance indicators)
http://amfone.net/Amforum/index.php?topic=29823.0(making a 5" hole in a non-removable aluminum panel)
If it can all be worked out, then it will be like having a 545A as a modulation monitor, except there will be no huge box of 60 tubes and there will only be a few possible display modes like:
*60Hz sweep-vs-RF
*60Hz sweep-vs-modulated B+
*trapezoid
*X-Y modulator grids-vs-plates
(I am shooting for a decent trapezoid and automatic beam killer as a first goal)
Other controls:
*intensity
*focus
*X position
*Y position
(astigmatism, beam rotation, & geometry will be screwdriver set)
The present topic of the CRT power supply is getting close to being built. I already tested the signal coupling and it works with a 1KW amplifier but may need hacks when put in the real equipment. I am waiting on some brackets for the 5300V power supply unit and to mock up that and the small power transformer before I make the power supply board, or maybe instead of a board, take those ceramic terminal strips from a Tektronix scope carcass here.
