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Steve Anderson wrote:Not really 'off topic' as you're using tubes/valves anyway.
I agree with all the author puts forward. I have a valve/tube mic pre-amp I built for when I'm using Skype or similar...for no particular reason, I just fancied doing it!
Very simple, an EF86 in triode mode plus a 9002 tube as a cathode follower. The heater for the EF86 is fed from DC to reduce hum, but the EF86 is well screened internally, so one could say it's not really necessary, but again, it's a whim.
Originally the EF86 was in the conventional pentode mode, but it had too much gain, around 44db (x160-ish), now it's 28db (x25). That's one of the trade-offs with triodes, lower gain, but that's what I needed. Schematic below, the original pentode version, I haven't created the triode version (yet). I may have posted this before...
Steve A.
Harry Dalek wrote:I like your preamp went from the transistor ,ic type to Valve evolved in a direction as every one seems to prefer the valves amplifiers..
Steve Anderson wrote:I don't want to open 'a can of worms' here, but there's no magic, no mystique, or anything objectively 'better' with valves/tubes. They obey the laws of physics as everyone and everything does. Sorry to any valve/tube audiophiles here. I like valves/tubes simply as they are a link to my past, and a link to our collective past. Nothing more. There are applications where tubes/valves are still better suited, but as time goes on they are becoming less and less.
So really, in the context we're dealing with here (not audio, despite my earlier posting) there are applications where vacuum-state electronics still are applicable. Here it's primarily interfacing with electrostatic CRTs, though there are now plenty of semi's capable of doing the same job.
As before, it's whim, a fancy, choose your own poison...
[/quote]I concede that a bunch of glowing tubes is better looking than a batch of 2N3055s bolted to a heatsink...
Steve A.
Steve Anderson wrote:Hi Harry, the 'bunching up' of the lines (i.e. the raster is brighter on the left) to the left of the display is possibly caused by the capacitor feeding the horizontal plate(s) being too small. Increase the 0.1uF (100n) to whatever you have, 1uF being a good start. Watch the voltage rating though!...and NOT electrolytic!
That's assuming the input waveform is actually a 'straight' and proper sawtooth.
There are one or two other things I'll come back to later...
wo things that really p**s me off in circuit diagrams, 1) Components not being identified, e.g. C1, R2, TR25 etc. in this case I can't say "The 100n on the anode of the 6AU6" as there's two of them! 2) No 'typical', measured or design voltages/currents shown...here, what is 'B+'? Anyone wanna guess?, or work it out?, you can, but you shouldn't have to...simple laziness and no thought for those who may use the diagram...
[/quote]I do my best in this regard, but I'm not infallible...
An example...supply voltage shown, and estimated current too (to be measured on prototype). Items in red my change, the circuit is still under development.
Steve A.
Klaas Robers wrote:Harry, you should realize yourself that the deflection plates of a CRT should be steered both, and in opposite phase. For a constant focus it is needed that the induced 'mean' voltage at the position of the deflection plates is constant, not changing with the deflection voltage. That will say both plates should contribute to the deflection, one in positive way, the other in negative way. So the idea of feeding just one plate with a saw tooth signal, and the other with a fixed voltage that you can adjust for centering control, is not Ok.
If you feed just one plate, you will see that the spot may be focussed at beginning edge of the screen, but unsharp at the end side. Adjusting the focus control will not help you; if you make it sharp at the end side, then it will be unsharp at the beginning side. I re-realized myself these facts when yesterday I jumped into the circuit diagrams of one of my Heathkit waveform / spectrum displays, the SB-620. It shows horizontal deflection problems.......
Harry Dalek wrote:...I was looking at trying this one only the deflection amplifiers since there dual triodes and better positioning controls and perhaps the cathode follower also, i should just adjust Steve's deflection amplifier to work all hollow state would this be possible Steve doing away with the 12v supply and 2n2222's?
Steve Anderson wrote:
Klaas is quite right, driving just one plate isn't such a good idea. It saves components (cost) size, weight, power consumption, and improves reliability. However, it produces defocusing, even on tubes designed for single-ended deflection. Here's the result on my 1CP1/DH3-91 1" CRT, it's designed for single-ended drive on the horizontal deflection. Note the defocusing to the left, whereas the centre portion is quite good....but what can you expect on a 1" (2.5cm) CRT?
This was the best I was able to obtain and followed the datasheet to the letter. It's not really meant for picture presentation, but AM modulation monitoring in transmitters. With a tube not designed for single-ended deflection it'll probably be worse.
As for the transistors, they could be replaced by a single resistor, BUT you'll also need a high voltage negative supply similar in voltage to the positive, but negative. Or replace the transistor with a pentode current source which will also need a high voltage negative supply and a separate insulated heater supply - take your pick!
There is a reason why 99% of CRTs use symmetrical deflection (as per above) and it doubles the sensitivity...and reduces the bandwidth requirements of the deflection amp(s), though that's not an issue here...
Steve A.
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