Moderators: Dave Moll, Andrew Davie, Steve Anderson
Harry Dalek wrote:Studying the circuits below can the Thyratron's be replaced by normal valves in this circuit ?
Steve Anderson wrote:[
Sorry, no. They do need to be gas-filled Thyratrons. I do have a book somewhere devoted solely to valve/tube timebases, not only Thyratrons, but normal (hard) tubes as well. If not too big I'll post it up later...
Steve A.
Later...Hmm, too large, nearly 40MB. I'll think on it...
Harry Dalek wrote:...! don't like the no transformer idea but the time base could adapted looking at that part...
Steve Anderson wrote:Harry Dalek wrote:...! don't like the no transformer idea but the time base could adapted looking at that part...
What's called a 'hot chassis' in the UK, though a very old term. I suggest no-one follows anything vaguely similar, it's simply unlawful these days due to safety concerns, DON'T DO IT!
Parts of the circuit could be adapted though it is designed for oscilloscope use. The B+ voltage was probably quite low being half-wave rectified from 110/120V, around 150V maybe...it's not an unreasonable starting point though...the 12AT7=ECC81.
Steve A.
Steve Anderson wrote:I have no idea what is being done in the first cct., an error I think...mainly around V5 and its heater...so dump that...
My own version, the transistors could be simply replaced with resistors, though to a somewhat higher negative voltage, not as linear, but probably good enough, say around -150V. The 1k's (Rxxx) would become 68k or 82k (1W) as a guess. Your power supply is becoming more complex...sure you want to continue? Especially if you don't want to use semiconductors in that too...
As for the last circuit...it's such a mess I'm not going to bother with it...guys, learn how to draw, it's not that hard!
Steve A.
The DG7-32 is a comparatively modern low-voltage CRT, if you're really serious in continuing with this, that's probably the CRT I'd select.
Of more concern to me would be the sync ccts, the video to the grid/cathode and the general size/weight/bulk and hidden expenses of this...but knowing you Harry, you'll manage it...it's something I wouldn't leap at, but good luck...
Steve Anderson wrote:Right, now, assuming you've decided to go with the DG7-32 the next hurdle is a suitable power transformer, something from an old radio as a start, 250-0-250V and a 6.3V winding. You'll need to add more to this in the PSU, but the HV bit is the most important. Current, if it's plundered from an old valve/tube radio, more than enough. alternatively as I have done in the past, use two transformers back-to-back. Look at old radiograms, old tape recorders[1}, record players, even jukeboxes[2}, anything with tubes/valves in it. Old TVs, though unless of historical value, rip 'em apart...
[1] Though plundering them I find a bit (more than a bit) upsetting...I have a 'thing' about tape recorders...
[2] Though probably worth a lot more if properly restored.
[/quote]Really, anything from the late 50's until the demise of tubes/valves is of no real value, though there are exceptions...
Steve A.
Harry Dalek wrote:..I think I have a Mu metal shield just see if it fits the neck of the DG7.
Steve Anderson wrote:Harry Dalek wrote:..I think I have a Mu metal shield just see if it fits the neck of the DG7.
I get around that problem by separating the required transformers into a box placed some distance away from the CRTs, then having an umbilical to the display itself. Not that elegant, but when you can't get the stuff (Mu-metal) there's not much of an alternative. The transformer box on the floor, the display itself a metre or more away on a two metre multicore cable, or individuals to get what you need...it solves a problem...when needs must...
Plus if you're clever the same 'transformer box' can be used for more than one display device...plug and play...
Steve A.
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