The Mongrel

[Harry Dalek]

OK, a pair of ECC85s and a pair of EF80s, that makes more sense than EF86s...I forgot about clicking the image, yet I often mention it! Your 6BX6s are the same as EF80s, just with US type number instead of European. As for the EEC85s, I think you have substitutes (or near) for them...I'll check.

Its nice to post a larger image i like the zoom great for schematic's like this ..Still need glasses i do .

Assuming this was for standard 625/50 (European language used on the circuit and 230V transformer primary) there'll need to be a few changes to component values for 32/12.5, I'll re-draw the circuit with suggested changes tomorrow....(Friday).

OH thanks Steve it sounds like this one is an easier solution adjusting this circuit ,i was interested to see if it was any good for the idea ,never have much luck with internet circuit posts..

Mid Europe job by the looks of it i think it was Czechoslovakia ,does the country still exist!

I assume you're not bothering with audio? Though it's no hassle if you are...

It was on my mind i have never made a monitor with one ! more than likely not but its always some thing i can add but have not had a need so far since learning to control the CRT has always interested me more .

I sent you some 630V or 750V capacitors a few years ago, I think they were 1uF or 470nF, can you try and find them and let me know? They could be very useful here...

Steve A.

I have used them a bit over the years in past monitor i must have some left they were the 470nf from memory have to check my capacitor tub

[Steve Anderson]

...never have much luck with internet circuit posts..

No surprise there!! The majority are dubious at best, many have no chance of working without some 'adjustment' (preferably with a hammer). Best to use datasheets/application notes from the device manufacturer, or something from a well respected publication, though even "Wireless World" made the occasional slip-up. Other sources include service manuals/datasheets from TV/radio manufacturers, things you know were made and sold in quantity, and therefore had to work.

Something that's a one-off, designed and built by a single individual (I include myself here), should be supported by waveforms, screen-shots and perhaps videos to show the validity of the design. A demonstration is a great addition, but when you're remote from most others (Harry and I) that's a non-starter. For those in or near the UK the NBTVA Convention is/was an ideal venue...one can only hope it resumes once we're through this pandemic.

Publication, or posting here, is another way of getting peer review. But remember, "Publish and be damned." There's also the NBTVA Newsletter, but like all printed matter it's S-L-O-W. Six months if you're lucky to receive feedback. That's just the nature of all printed publications.

Steve A.

[Harry Dalek]

="Steve Anderson"
No surprise there!! The majority are dubious at best, many have no chance of working without some 'adjustment' (preferably with a hammer). Best to use datasheets/application notes from the device manufacturer, or something from a well respected publication, though even "Wireless World" made the occasional slip-up. Other sources include service manuals/datasheets from TV/radio manufacturers, things you know were made and sold in quantity, and therefore had to work.

I was trusting of magazine circuits till the 73 magazine a few years ago showed me they didn't check if the schematic was correct ,i am sure the original worked but the drawing of the schematic was wrong .

Something that's a one-off, designed and built by a single individual (I include myself here), should be supported by waveforms, screen-shots and perhaps videos to show the validity of the design. A demonstration is a great addition, but when you're remote from most others (Harry and I) that's a non-starter. For those in or near the UK the NBTVA Convention is/was an ideal venue...one can only hope it resumes once we're through this pandemic.

mmm Yes proof of it working and waveforms show and tell do help ...same any where these days a design read and perhaps copied by some one at great distance magazine or internet site ..so all we want its a correct schematic .

Publication, or posting here, is another way of getting peer review. But remember, "Publish and be damned." There's also the NBTVA Newsletter, but like all printed matter it's S-L-O-W. Six months if you're lucky to receive feedback. That's just the nature of all printed publications.

For sure the old way is pretty slow these days this is sort of like an undated Newsletter but live to the seconds if want or need be ...

[Steve Anderson]

I was trusting of magazine circuits till the 73 magazine a few years ago showed me they did check if the schematic was correct ,i am sure the original worked but the drawing of the schematic was wrong.

That happens. Often an author sends in an item to be published following the editors instructions, typed and double-spaced. no problems there. Diagrams are different. Previously the majority would have been hand-drawn and the text within the drawing done by hand too. There's generally the source of errors and ambiguity. That's assuming the original/intended diagram is valid in the first place.

Preparing diagrams for magazines or books via a printing-press is a slow, time consuming, therefore expensive and an error prone process. Until now. With computers there's no excuse. Magazines may 'Pretty them up' to suit the publications 'style', otherwise the onus has shifted back to the author. And in my opinion that's a good thing. Proof reading is reliant on the proof reader understanding the subject matter, with something as specialised as electronics, that's not always the case. Especially where there may be some heavy mathematics involved. (Often). The same proof reader may have a gardening magazine next, maybe they do know something about that (not me).

So genuine errors do creep in, it's a fact of life. However, there's a lot 'out there' that's simply published to fill up pages with supposed interesting, accurate though erroneous articles, merely to keep the circulation numbers up (or 'likes' etc.) and the advertisers happy.

Steve A.

[Steve Anderson]

Some data on the original CRT used in the display that Harry posted a while ago...sadly most/all of the information is in Russian (maybe)...

The original schematic is a bit confusing until you see the comment near the CRT symbol, "Obrazovka je otocena o 90 (degrees)", I'm assuming that means, "Tube rotated by 90 degrees". If so, it all then makes sense...

Note the deflection plates are brought out through the side-glass and not the base to minimise capacitance. Designed for some serious high frequency work...in its day...

I've made a start on re-drawing the original schematic, but I doubt I'll complete it today...just interruptions...

Steve A.

13LO3I.pdf

(1.05 MiB) Downloaded 194 times

http://lampes-et-tubes.info/cr/cr016.php?l=e

[Harry Dalek]

That's ok Steve no worries we have 3 Birthdays in a row so i can't get near a soldering iron for a while yet .

[Steve Anderson]

Currently working on the deflection amp(s) for this. Below is the load-line when using the ECC85s, now I have to get the tubes you have to behave similar. Also the original CRT must have been quite sensitive regards deflection, and/or it was run at the minimum possible voltages. The ECC85 load-line is in red, and the operating point approximately where the blue circle is. I'm not saying it's ideal, but gives you an idea of what has gone before...the result isn't as linear as I would like though...maybe the original designer had limited tube choice also...

The ECC85 was really intended as a R.F. amplifier and an oscillator...

Steve A.

[Harry Dalek]

Currently working on the deflection amp(s) for this. Below is the load-line when using the ECC85s, now I have to get the tubes you have to behave similar. Also the original CRT must have been quite sensitive regards deflection, and/or it was run at the minimum possible voltages. The ECC85 load-line is in red, and the operating point approximately where the blue circle is. I'm not saying it's ideal, but gives you an idea of what has gone before...the result isn't as linear as I would like though...maybe the original designer had limited tube choice also...

The ECC85 was really intended as a R.F. amplifier and an oscillator...

Steve A.

Thank you Steve ,Looking it up the the ECC85 used in front end stages of FM radio receiver's VHF tube for use in b/w TV sets mine would not have to run that high ,i am not sure with this valve if there's a lower range it works on ,i have 6BM8 Audio Dual Package, Triode,12AT7 twin triode Audio ...from a quick look .

My side first day i could touch the case for a few days i have been looking into making a panel plate for this , it was a case of redoing CRT mounting face plate behind it cutting another big hole , needed to do this to let me add controls to the panel when needed ..an on off switch for the Ac supply is a good start ! So getting that out of the way for the time i can work on the circuits and powering them .
Least this is done but need panel control holes more drilling .

[Steve Anderson]

As it turns out the 12AT7/ECC81 is quite close to the ECC85, near enough anyway...though I'm still troubled by the nonlinearity...

The first stage (also an ECC85) can be replaced by many others, here with NBTV it's really just an audio amp, nothing special...note the input is a grounded grid arrangement, low impedance. Fine for video sources of 75 ohms, but not audio gear. So that'll need modifying...to get around the inversion of a grounded cathode stage, we'll make it grid modulation of the CRT rather than cathode...it also means that you're not driving the CRT transformer capacitance with video...

Also the sync polarity becomes inverted and somehow we need to deal with the 'missing sync' rather than conventional 625 frame/field syncs...

Steve A.

[Harry Dalek]

As it turns out the 12AT7/ECC81 is quite close to the ECC85, near enough anyway...though I'm still troubled by the nonlinearity...

The first stage (also an ECC85) can be replaced by many others, here with NBTV it's really just an audio amp, nothing special...

Steve A.

OK so that's good the 12AT7 useful then ,nonlinearity here we are talking it in the deflection amplifier circuit i see its used there and the input amplifier ? i was thinking it was more of a problem in the ramp generator if that ones going to be used ? I would be lost here trying to correct that .
CRT Grid modulation sounds good to me ... i am used this .

[Steve Anderson]

...I was thinking it was more of a problem in the ramp generator if that ones going to be used ?

The ramp generators I plan to 'breadboard' (the EF80s/6BX6s). Trying to analyse them on paper...no thanks! However the breadboarding make have to join the queue of other stuff...all non-NBTV/SSTV...

Re-read my posting above, submissions 'crossed'...

Steve A.

[Harry Dalek]

...I was thinking it was more of a problem in the ramp generator if that ones going to be used ?

The ramp generators I plan to 'breadboard' (the EF80s/6BX6s). Trying to analyse them on paper...no thanks! However the breadboarding make have to join the queue of other stuff...all non-NBTV/SSTV...

Re-read my posting above, submissions 'crossed'...

Steve A.

You do well working it out on paper as much as you do 1 am hopeless at all that ,when you can Steve ,making it as a working circuit will show how well it works ,i know all this takes longer .I still have a bit to do just to get the AC side up and running i hope by the end of the week i have wired it up .

[Steve Anderson]

Harry, I wouldn't start on the power supply yet, we still don't know what voltages and currents are required. I understand you wish to get on with this, but patience is required unless you're happy to re-work things over and over in the future...

Steve A.

Interesting link found here, though you can forget the RF, IF & detection parts...even so, it shows what you're set yourself up for! It's worth following the link at the end to view the hi-res photos...and it was written from an Australian perspective...

https://www.cool386.com/5BP1/5%20inch%2 ... eiver.html

[Harry Dalek]

Harry, I wouldn't start on the power supply yet, we still don't know what voltages and currents are required. I understand you wish to get on with this, but patience is required unless you're happy to re-work things over and over in the future...

Steve A.

No i was not starting any DC construction Steve i just want to get to the point to power up the Transformer ,i had no front panel so i was just working on that so i can add a mains switch and perhaps an indication on off lamp for a start .
I know its a bit pointless starting the DC supply till you know what the circuits need .
Just thinking about ways to mount the boards stuff like that till i get some thing to build ... So no problems this end .

[Steve Anderson]

...till I get some thing to build...So no problems this end .

All OK, though I think I'm going to need some help with sync separation and a few other matters, we'll see...that's if it has to be tube based, semis, no problem...

One thing I have never done is a P7 CRT type SSTV monitor. I guess I should really do it so I can 'experience' what those in the 60s had to go through...I have (so my last stock-check tells me), two DP7-5 CRTs, the same idea as P7 CRT and 3" diameter. Not as low voltage as a DG7-32 (DP7-32) but no real hassle either...as before with the DG7-32 NBTV monitors it'll be a hybrid.

The only thing I'm concerned about is the quoted line-width at 0.7mm which means you'll lucky to get maybe 100 lines of resolution...but then again the old 72-line DG7-32 didn't seem that bad, however, this is a step-up from that...

Steve A.

If I do go ahead with this it'll be in the SSTV section...anyway, I've got a bucket load of other stuff to do, so don't hold your breath!