Morning all...

       it's ten to four on a Tuesday morning, and I'm at work. This is not right. Ah well....

       I may need to look in to the possibility of changing the tube on the Avant; does anyone know where to get one from, or a good place to take it to? Simon of AVA services in Coulsdon (beneath the B&O shop there) has been recommended to me...

       Thanks -

               Alex.

Hi Alex,

I would think the staff in the B & O shop above Simon will have heard whether he  'cuts the mustard'.  Ask them & then ask Simon for a quote if their answer is favourable.  I have a feeling the answer will be 'Yes!'  Good luck!

John

Tube cost is circa £350 from B and O ... budget for about 3 hours of work.

Neil

....That is, if it's a 100 Hz (type 83XX), a 50 Hz (T81XX) becomes even more expensive because they put a different type of tube in which requires an adapted deflection board.

Now to my knowledge Philips lowered the price of new tubes to about 200 euro but B&O increased the prices....but so far i didn't find an alternative source to buy the Avant tubes, maybe someone knows ??

Perhaps I should look further into the problem... the picture is fine except for the green channel, which appears to be completely out of control - when no image is being displayed the screen has a dark green tinge all over with faint lines through it. Is this repairable? My knowledge of TV control mechanisms isn't fantastic, but I presume that that means one of the electron gun focusing/scanning plates has died. I have a horrible feeling that that isn't going to be the kind of thing that can be changed separately...

Any thoughts, guys?

Alex 

Not so fast.......   with a little patience and a Sencore CR-7000 CRT analyzer this can likely be fixed.  Now, it could be a heater to cathode short as well, which CANNOT be burned away with the sencore.  BUT....  I have had great success by overheating the cathode by momentarily increasing the filament voltage to 150-175% of normal.  Let cook for 30 seconds to a minute and cool.  Test the tube.  Repeat if needed.  It's a last ditch effort IF a replacement CRT is not available or prohibitively expensive.

Anyhow... I repair broadcast video monitors for a living, and sony trinitron tubes are the most difficult tubes to reclaim.  I have had great success overall.  Most other types respond a lot better.  The Beovision uses a non trinitron tube, so prospects are better.

So you'd need someone with a CR-7000 to look at it.  The tube is un-usable as-is, nothing to loose by trying.

Good luck!

Marc
 

Actually, you want to use a variable DC powersupply to heat the tube.  I am not sure myself why this often works, but my theory is that the much higher temperatures causes the cathode and filament to over-expand.  When it cools back down, often the filament has been pushed just enough away from the cathode to "not short".

The sencore is used to find out WHAT the problem is to begin with, as well as life-test the tube.  Often a low level cleaning run on the cathodes will also bring back the full brightness of the tube.  I have both a CR-70 as well as a CR-7000.  The main difference is that the CR-7000 can test all 3 guns at the same time and it's GENTLER on the cathodes.  I used to strip trinitron cathodes with the CR-70.  I had to buy a 7000 after sencore assured me that this won't occur with this model.  And it hasn't.  Although I can still wipe out the tube on the higher settings.

I repair and calibrate broadcast studio monitors, so still have a need for the Sencore.  Flat panels still cannot be used for color critical editing, so I have a great niche market.  Especially in Los Angeles.  

Anyhow, the point is that tubes are getting VERY scarce.  If you can save the tube, it's fantastic.  If all fails, the tube was bad anyway.  But to do nothing......   Personally I'd rather try it first.

So, on a 6.3 volt heater I'd go up slowly to as much as 11 volts and let it bake for 60 seconds.  Then test.  Rinse and repeat as needed.  Tube is shot anyway, even if you blow out the filament.  Nothing to loose.  

Maybe a 3rd option, and this doesn't work on all sets.... a filament/cathode isolator.  TV shops used to use them for this.  It's a transformer that is wired into the filament leads to isolate the filament VOLTAGE from the cathode.  The potential remains, but it can't bias the cathode on, so you loose the green (or red or blue) background.

Well, glad to help, so ask away anytime.

Marc 

Many thanks, Marc! Now, where did I put my Sencore 7000?

I'll pass this on to Simon, see if he thinks it's possible and whether he has the tools - if this works this could be a very useful procedure, as you say, there are many sick and dying Avant's out there and it would be nice to be able to expand their lifespans. It's either this, or find out whether there is any other tube (eg Philips) that can be used to replace it.

Don't forget.... this takes a certain "feel" to do, as well as knowing what the particular tube type can take.

As to replacements, similar tubes can be swapped.  I do this a lot.  They have to be in the same family, but it's also possible to

make a custom socket adaptor if the pins are different.  The basic voltages need to be close to avoid modifications to the set itself.

A good "old school" tv guy should be able to do all this.  Pity that modern techs are mostly board swappers.  

Yes, you can heat and tap it as well.  But not too hard.....

Some people face the tube down, the theory being that any contaminant will fall harmlessly into the bell.  However, between the cathode and the front of the tube is still the entire electron gun structure, so this probably doesn't actually work.  I never do this.  I shoot tubes with the back off the set sitting normally on my bench.  Worked fine for 20 years.  The only difference is that I have modified my procedures over the years to reclaim heater to cathode shorts which "cannot" be removed by zapping it.  (A high current discharge between the cathode and filament WILL burn away the short, but blow open the filament at the same time.)  Anyhow, you have nothing to loose.  In cases where a CRT is still "OK" but a bit soft, I refuse to shoot it.  Since it's still entirely watchable, the risk is too high.  But if it's really hosed..... sky's the limit.

Marc