Notifications
Clear all

"Like peeing in a wetsuit" design

 
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

In case you hadn't heard the term the follow-on is "It gives you a warm feeling but nobody notices".

As a design engineer I've always had an interest in why certain design features were added when no-one can tell the difference. Sometimes I suspect it's to support a marketing claim.

Like this example from Philips Australia in the early to mid 60s that modulated the focus voltage so that you could have good focus at the sides as well as the centre of the picture..

Now with a 23 inch CRT you'd have to be within a metre or so of the screen to see the difference, and then only if it was pointed out to you.

T301 performs the magic, deriving the signal from across the B+boost cap.

I think the TVs that had this circuit also sported a "Power Focus" badge. Maybe they also had stickers on the screen that encouraged showroom visitors to compare the difference?

Anyway, has anyone ever seen this on other designs?

I have a few more examples if anyone is interested in this train of thought. Like the modulated horizontal S correction used on the first (110 degree delta gun) Krieslers. You could only tell the difference by carefully examining a test pattern, again knowing what you were looking for! Yes, all the crosshatch lines were indeed ruler straight and evenly spaced, all over the screen!

 

ReplyQuote
Topic starter Posted : 25/07/2020 5:11 am
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

Here's the circuit, I hope. Got blocked by Wordfence from attaching it to the edit (it's only 157k)

Power Focus

 

ReplyQuote
Topic starter Posted : 25/07/2020 5:22 am
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4143

I can’t remember if TV’s I worked on altered the focus with the scan, but expensive colour displays did use this technique. They also had CRT’s with finer shadow masks, or so I was told. These were expensive monitors for special use, not the usual desktop computer monitor.

The operator was no more than 18 inches away from the screen not the usual TV  viewing distances.
I never had to repair these devices, just saw them in use.

 

ReplyQuote
Posted : 25/07/2020 6:18 am
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4143

@irob2345

I would be interested in those designs, I can’t guarantee to remember if they were used in the U.K. sets though, seem to have forgotten so much about the sets I used to fix.

 

ReplyQuote
Posted : 25/07/2020 7:54 am
peterscott
(@peterscott)
Prominent V-Ratter Registered
Posts: 971

Could have done with that in the very earliest B&W sets too. (see here)

ReplyQuote
Posted : 25/07/2020 9:18 am
Lloyd
(@lloyd)
Noble V-Ratter Registered
Posts: 1523

I'm sure I have 2 examples of this, one is in the Samsung Slimfit, and another is in a Sony flat faced Trinitron PC monitor, they all have 3 pots down the side of the LOPT.

Regards,

Lloyd

ReplyQuote
Posted : 25/07/2020 5:31 pm
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

Here is another circuit, this time from an early Oz HMV F3. What's interesting about it is that it avoids the need for a vertical linearity control and any high voltages on pots. HMV continued to use this circuit in various forms even into the days of the hybrid sets, in this case replacing TR5 (the current to voltage transformer) with a transistor.

HMV in Australia was a very different animal to HMV UK, but I wonder did this idea appear in any UK designs? The use of current sensing feedback is pretty standard in solid state designs but this is the only example of its use in valve circuits that I know of.

Note also the split secondary on the vertical output transformer. This was to cancel out horizontal crosstalk through the yoke that would have degraded the interlace performance.

HMV Vert

 

ReplyQuote
Topic starter Posted : 28/07/2020 2:08 am
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4143

@irob2345

I have not seen that before, one reason I think of it not being popular is the cost. A wound component as opposed to a few R and C’s and a cheap pot. UK set makers liked to trim the build costs to a minimum.

 

ReplyQuote
Posted : 28/07/2020 7:33 am
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

Yes that's what other setmakers here did too. HMV TVs had a lot of wound components (that model had push-pull audio and two filter chokes), all made in-house so that might have had something to do with it. It did result in a reliable design that held its settings despite valve aging. And of course a trim pot with a Kv pulse on it was never going to be a lasting proposition.

ReplyQuote
Topic starter Posted : 28/07/2020 7:44 am
Till Eulenspiegel
(@till)
Famed V-Ratter Registered
Posts: 4526

Early dual standard KB TV sets employed a line eliminator circuit to remove the apparent line structure of the 405 picture.  There was no modulation of the CRT focus electrode voltage but by applying an adjustable  negative voltage to the focus electrode to alter the shape of the spot.

Circuit used in models  VV30, VV70 and VV80.

From the 1963/64 Radio and Television servicing book:

Line Eliminator Circuit

KB VV30 Line Eliminator

 This device is fitted to models VV30, VV70 and VV80 to provide a means of softening the line structure, mainly on 405 lines. Rectification of the line flyback voltage provides a 500 volt negative voltage which is applied to the picture tube focus electrode.

Till Eulenspiegel.

ReplyQuote
Posted : 28/07/2020 10:36 am
Nuvistor liked
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

Otherwise known as "spot wobble", this was a feature of the special monitors that were used in Telerecorders that allowed early television programs to be recorded on film. Although the way this worked was by feeding a much higher frequency (ca 10MHz) into the vertical deflection yoke.

This became more important because, to record onto film, you needed to allow for the film pull-down time between frames. So as to allow enough time for this to happen without ripping the film to shreds, each alternate frame was blanked, leaving only 202.5 lines of vertical resolution.

By running the image on the monitor as a negative, you could use the developed print immediately, without having to perform a contact print.

To see what this looked like, you just need to watch some very early episodes of Dr Who or the Queen's coronation.

ReplyQuote
Topic starter Posted : 28/07/2020 12:17 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered
Posts: 4143

@irob2345
Ekco TV’s in the middle 1950’s used that spot wobble technique, it could be switched off and I don’t think many customers I had used it.

I didn’t know about the KB circuit, not surprising in that we didn’t see very many for repair. 

There we were trying to get the sharpest picture and along came these designs to soften things up. At normal viewing distances I didn’t have a problem with the 405 line structure on most sets, only the larger screen 21inch and above starting to show the problem. I am still of the view that the content is king, I would rather have a less than perfect picture on content that interests me then a perfect 4K one with dross. I shouldn’t call it dross, some one some where must like it.

 

ReplyQuote
Posted : 28/07/2020 7:22 pm
irob2345
(@irob2345)
Reputable V-Ratter Registered
Posts: 289

Yes a PM5544 displayed perfectly looks nice, but terribly boring!

I'm gradually building up period-correct (and worth watching) content for my small collection. I must admit I try for content that originated on videotape, like the early 60's Crawford Productions "Homicide".

ReplyQuote
Topic starter Posted : 29/07/2020 2:01 am