TV to watch Queen's Christmas Speech on?

[bobhowe]

Hi Trevor David has more DAC90s than me

[FERNSEH]

Hi Bob,
I counted the collection DAC90s and DAC90A sets today and found I only have eight.

DFWB.

[FERNSEH]

Even after completely disconnecting the EHT overwind from the circuit the picture width fault remains and is the only obstacle to having the set ready for Christmas Day.
There's nothing to lose by removing the EHT winding because the tripler works very well in this set.
The video waveform to the CRT cathode is AC coupled thus causing the DC component to be lost but as the EHT regulation isn't very efficient it's better to leave the circuit as it is.
The line hold is rather critical. Very simple direct line sync coupling employed in this set.
A small value capacitor between the anode of the sync separator valve (12AX7) and the anode of the blocking oscillator valve, the triode section of a PCF80.

DFWB.

[FERNSEH]

Yesterday, the EHT winding on the line output transformer was removed.
Results are encouraging. The EHT at normal brightness is 17.5KV rising to 19KV at zero beam current. As mentioned before the EHT regulation in this set isn't good.
With EHT voltages like this and supplied from a tripler the peak voltage at the anode of the 50CD6G line output is very close to maximum permissible for this valve. That is, 6,600V for 15% of the scanning cycle and not more than 15microseconds duration.
After the overwind was removed the set was allowed to display the test card for thirty minutes.
Later KB TV sets including models with 110 degree CRTs employed the PL81 as the line output valve. The huge 50CD6G fell out of favour with set designers.

DFWB.

[bobhowe]

Hi David how did you manage to remove the EHT winding ?

[FERNSEH]

"Hi David how did you manage to remove the EHT winding?"
Hi Bob, Used a hacksaw. The overwind put up a fight and working close to that huge tube was a bit scary.
Switched the set on this morning. EHT measured 17.5KV. Turn the brightness control fully up and the EHT falls back to 15KV, the same figure as it was before the overwind failed.
A beam limiter will be introduced into the CRT circuits.

DFWB.

[bobhowe]

Hh David please post some pictures

[FERNSEH]

The off-screen pictures were taken yesterday evening.
The 405 line structure is very prominent and looks even worse because the camera captures only one field.
Viewed from a distance of ten feet the picture looks absolutely fine.
Interlace has to be perfect with such a large screen.
Other jobs to do. First, get rid of that chassis support frame.
Second, raise the shelf in the cabinet to compensate for the removal of the frame.
Third, shorten the pre-set controls cables. See first attachment.

DFWB.

[peter_scott]

David, The second screen shot looks like it captured the full frame. Would your camera not extend its shutter time if you just reduced the brightness of the screen?

Peter

[bobhowe]

Originally Posted by FERNSEH

The off-screen pictures were taken yesterday evening.
The 405 line structure is very prominent and looks even worse because the camera captures only one field.
Viewed from a distance of ten feet the picture looks absolutely fine.
Interlace has to be perfect with such a large screen.
Other jobs to do. First, get rid of that chassis support frame.
Second, raise the shelf in the cabinet to compensate for the removal of the frame.
Third, shorten the pre-set controls cables. See first attachment.

DFWB.

Hi David great picture you are on the home straight

[FERNSEH]

Originally Posted by peter_scott

David, The second screen shot looks like it captured the full frame. Would your camera not extend its shutter time if you just reduced the brightness of the screen? Peter

Hi Peter,
I use the Samsung A12 to take the pictures. Should be possible to change the shutter speed so that both picture fields can be taken. Reducing brightness will help also.

Hi Bob,
now it's those cabinet alterations to attend to.
I'm hoping when the pre-set controls cables are shortened the stability of the line sync will be improved.

DFWB.

[bobhowe]

Hi David glad it was just the EHT winding at fault

[murphyv310]

Hi.
The HMV 2807 is getting closer to its first test. If there is life in it we then will need to see what tube to fit to the set to obtain a watchable picture on. This part will be the biggest challenge.

[bobhowe]

Originally Posted by murphyv310

Hi.
The HMV 2807 is getting closer to its first test. If there is life in it we then will need to see what tube to fit to the set to obtain a watchable picture on. This part will be the biggest challenge.

Hi Trevor got Beer in for Davids Queen Speech set hope to see yours done for the New Year Countdown as I Will get some more Beer for your set

[The Philpott]

- Don't forget the Royal Institution Christmas Lectures! No-one else in the household will watch them so i will slope off upstairs despite any protest...it has to be done. Unfortunately this year it's about viruses (for crying out loud!!)
Dave

[FERNSEH]

Earlier in the discussion about this set I mentioned it was my intention to remove the metal framework attached to the underside of the chassis.
It's not a KB component so it should not be in the set.
Removing the chassis support will entail repositioning the shelf inside the cabinet upwards 20mm.
The blockboard shelf was chopped out yesterday evening. Note those nasty nails. A new shelf will be made from 12mm plywood, a material one would expect to be used in a TV cabinet.
A much larger loudspeaker should be fitted. the original unit was a tiny thing, a 10 X 6 'speaker will be fitted.

DFWB.

[murphyv310]

Plenty of acoustic wadding in there David, a tweeter, crossover and a hidden 3-3 amp for good quality.

[its ur aerial]

Originally Posted by rambo1152

I wonder what HM herself watches them on (the ones she didn't do live).

I always imagined she must have a Dynatron with the Royal Warrant.

Looks like it's been discussed before.
https://www.vintage-radio.net/forum/...d.php?t=109247

I know Dynatron had a Royal Warrant, but so did DER, but I can't remember now who in the Royal Family it was for, I actually think DER had two, Prince Charles and possibly the Queen Mother, I am really not sure now.
I know I applied for the Royal Household job when a vacancy came up, but didnt get it ! From memory there was 3 DER Engineers and a Aerial Rigger
working out of Apex House, looking after about 200 sets ! Spread over Windsor Castle, Buckingham palace, Kensington Palace and St Jame`s Palace.
It was considered a right cushty little number.
Ken, G6HZG.

[FERNSEH]

The metal framework has been removed from the chassis, only to reveal more horrors. The brackets that attach the chassis to the cabinet shelf have been almost cut off.
The wires between the chassis and pre-set control panel have been shortened.
Apart from looking a lot tidier, inter-reaction between the control functions is no more and the interlace is perfect irrespective of frame hold control setting.
Third attachment shows the tiny sound output transformer.

DFWB.

[murphyv310]

Hi.
The 2807 is now very close to completion bar one thing...... The CRT. I'm collecting one on Thursday through Edinburgh's busy streets which I never look forward to. So let's hope there is at least a glimmer from this tube. I can see watching Her Majesty with the blinds and curtains closed, even the Christmas tree lights will be turned off!!
At least it'll be watched on her father's favourite TV Receiver.