Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:I don't have full data on the 5FP7A, only abridged, but I do on the 5FP7B. The difference is usually minimal and in most cases can be ignored.
As you'll note, it's again magnetically deflected and focused, more than likely developed for long-range radar applications as noted in the datasheet.
To eliminate some possible types, how many pins are on the base? (Including any missing ones, common on CRTs)
Steve A.
Steve Anderson wrote:I would forget what's on box, and if you are sure that the markings on the tube itself are clear enough, go with those. The box probably has simply been re-used.
Not uncommon with older stuff generally. Obliterate the existing box makings and add the correct one(s) when you are sure. Or find/make a new unmarked/correctly marked box and throw out the old one....so there's no confusion in the future.
The fact it only has 8 pins is also a pointer in the direction of it being at least a magnetic deflection CRT, possibly focus too. The datasheet I have for the 5AP1 and 5AP4 indicates it has an 11 pin base, all electrostatic, so I don't think you have a 5AP7(A) there. The 'A' suffix usually makes little difference...
Steve Anderson wrote:Here's a CRT I would love to have, excellent for demonstrations. you can see all inside...
In this case the deflection plates are brought out on dedicated terminals to reduce capacitance in the deflection circuits. In this case around 8 pins, maybe less, on the base should be enough...this is a Philips DG16-1 with a medium persistence green phosphor, for general oscilloscope and demonstration use. Its construction is just as the textbooks show, it's then those invisible electrons can be easily seen (well, they can't) doing something...producing a result on the screen...
Steve A.
Harry Dalek wrote:Yes the big pain on this one is more the focus coil which would have to be made i have some data on this in an old magazine ,the SSTV i made in the about 1990 i was lucky enough to be given a focus coil long gone now ..but i recall after some use the coil would warm up and and defocus a bit . Wonder if you could get a ring magnet big enough for some thing like this mmmm
kd2bd wrote: I'm beginning to think your tube may have been manufactured to specifications of a specific client and application, and may not have been available for general use. 73 de John, KD2BD
kd2bd wrote:I found some additional information on the 5AP7 CRT here:
You might be able to find more clues by carefully examining what you can see of the gun structure. Comparing the physical dimensions of your tube versus the 5AP7 datasheets might help determine if your tube is indeed related to a 5AP7, or is something else entirely. I'm beginning to think your tube may have been manufactured to specifications of a specific client and application, and may not have been available for general use.
Entirely possible. The radar CRTs that Decca used (9", 12" and 16") where made by someone (I've forgotten who) to their specification. The phosphor was P7-like, but also to their own 'special brew'. The type designation was nothing like what we're used to, 5BP1, DG7-32 and so on, but a unique 'house number'. (Also forgotten). I wish I had 'borrowed' a couple while I worked there. I also regret not 'spiriting away' a bunch of circuit diagrams.
kd2bd wrote:
As the temperature of the focus coil increases, its resistance increases and the current flowing through it decreases, changing the CRT focus. Since the coil's magnetic field (and level of focus) are based on current flow rather than voltage, it might be worth trying to drive a focus coil through an adjustable constant current source rather than an adjustable voltage source. With the coil being fed by a constant current source, the current flowing through the coil will remain at a fixed value, as will the level of focus, regardless of the coil's temperature. Many of the popular 3-terminal DC voltage regulators (LM317, etc) can be configured to serve as adjustable constant current sources.
[/quote]When my interest in SSTV first developed in my teen years, I liked the idea of using a fixed magnet for focusing much better than having to supply DC power for a coil (or a high voltage for electrostatic focus). I was lucky to come across what I believe is an old Quam Focalizer permanent magnetic focus assembly that worked well with my 7BP7. It would be interesting to see what might be constructed today using an array of small modern neodymium magnets.
73 de John, KD2BD
kd2bd wrote:Some information on the Quam "Focalizer" and its use with a 5FP7 and similar CRTs can be found here: https://labguysworld.com/5FPn_CRT_Tester.htm
Either a ring magnet or a series of small bar magnets can be used to build your own. The tough part would be to construct an adjustable magnetic "shunt" between the magnet(s) and the tube to simultaneously confine the magnetic field to a narrow "gap" of maybe 10mm or so, and to adjust its amplitude for proper focus. The article referenced above explains how this works.
73 de John, KD2BD
Users browsing this forum: No registered users and 21 guests