The MW6-2

[Murphyv310]

Hi.
After I posted up the photos I made up a Ramp Generator with a 555 for line drive, I tapped off the sync from an LM1881 for the line generator and have also fed frame pulses from it to the TDA1170S. A quick lash up amp shows the line locks perfectly and the picture is the right way round!!!!
I also have greatly improved contrast by using a 1j29b rod pentode, its all strewn over the bench and as we say up here it "looks like a pound of mince" not to worry as I have some ideas for the completed project.
EHT though will need to be increased and I'm actually wondering if the Chinese EHT unit will really be up to the job. I'll get a little more time tomorrow with it but not on Wednesday.

[`FRANK.C]

Hi Trevor
Your making great progress. Those small tubes produce incredible pictures. looking forward to see how it works out.

Frank

[Murphyv310]

Hi.
A long time since I did anything on this. Too many changes have happened since October 2018.
The recent B16T restoration and the use of the MW6-2 for testing has confirmed that this tube will run perfectly around 6 to 7kv EHT.
My idea is to resurrect this but using rod pentodes especially the high power ones that are good for pulse operation.
I've already confirmed that a 1j29b works perfectly as a blocking oscillator for both line and frame frequencies. I've suitable frame output and line scan transformers so this will definitely work.
So I'll update this thread over the next week.

[Murphyv310]

Hi.
The shortwave TX test project has now been dismantled and the board will be used as the timebase panel with video output and sync. I will be mounting this on an alloy box chassis underneath. the Line and Frame output transformers will be mounted above the chassis along with the power supply items. I intend to run this with the two DC to DC I used on the TX project certainly initially.
Once the timebases and video section has been tested and found to be satisfactory or other I will then decide to either make an RF stage or not. If this initial work is good then I will need to decide whether I should go the route of a TRF or Superhet, again using rod pentodes.
May start next week.

[Geordie McBoyne]

The MW6-2 shown in the attachment was taken out from the Philips 600A projection TV set I've been working on during the lockdown period. After finally getting the line timebase to work and sorting out the tube protection circuits a very dim picture could be seen on the screen when the workshop lights were extinguished. 
A replacement tube was found in the shop and duly fitted. Picture is slightly better but it's still a lights out job to see anything on the screen. A vivid picture can be seen on the CRT screen.

Geordie McBoyne.

[Murphyv310]

I've never seen one as bad as that. I've one with a distinct spot but otherwise very bright.
I've another couple with a burned in 4x3 section that is from years of use. This burning reminds me of cctv monitors that have displayed the same picture for ages.
Somewhere I read it was down to X radiation which I very much doubt.

[Murphyv310]

Hi.
Well as line oscillator and output rod pentodes will and do work. Using a 1j29b as a blocking oscillator and two 1n24p as output, BY223 as a recovery Diode. Although this works it is pushing the 1n24p as a pair quite hard. The line output tx is a thorn 900 jelly pot.
See this video.
https://youtu.be/k-Q3IpiEOK0

[Geordie McBoyne]

Even when operating with an anode potential of 25KV the deflection power requirements of the MW6-2 are quite modest, I can affirm this by the fact the timebase circuits of the Philips 600A projection TV set are very similar to the 12" CRT direct view models 385U and the like.
I believe the deflection power requirement is a function of the square of the EHT voltage so if the MW6-2 is operation with say, 5KV it won't be the simple matter of the deflection power being five times less than 25KV is.
The MW6-2 has a smaller neck diameter compared with the direct view tubes so that helps to reduce the deflection power demands.
Anyone know the deflection angle of the MW6-2?

Geordie McBoyne.

[ppppenguin]

For magnetic deflection the required field increasers with the square root of EHT, not the square. There was once a time that I could derive that from first principles. So four times the EHT, only twice the deflection power. Unlike electrostatic deflection where the deflection voltage is proportional to EHT.

At high EHT voltage, the electron volocity will be high enough that the electron mass will increase significantly due to relativistic considerations. This will raise the deflection power needed. I don't know (and can't be bothered to work out) if this makes any significant difference in any domestic CRTs.

[Jac Janssen]

Anyone know the deflection angle of the MW6-2?

Geordie McBoyne.

A Philips datasheet specifies it as max 67.5°.

   

Jac