Introduction and questions re TV22

[HamishBoxer]

Having restored a few TV22s,it is difficult to get a raster on some with no signal fed in.

[G0PKH - Pete]

If some heaters appear very bright, and the tube heater quite dull, could it be possible that you may have missed a capacitor hidden in the heater chain somewhere which maybe leaking.

[Geoff 555]

Thank you Hamish and Pete fed in a signal and have a strong test card tone but no tube action, the valve heaters seem to be All bright, but I have nothing to compare them with so may be that is how they are, the tube heater is just an orange glow that can only be seen properly in complete darkness. I probably wouldnt know if I had missed a C but I will have a look.

Cheers.

Geoff.555

[SWB 18]

Hello,

Just wondering if you discovered that capacitor that Bush fitted under the tag board which is installed underneath the centre of the main deck.

Could you confirm the type number of the crt you have fitted, please?
I would expect you to have an MW22-16, 6.3v 300mA heater with a B12A base, but wonder if a Mazda CRM93, 12.6v 300mA heater also with a B12A base, might have been substituted over the years?

Regards,

Phil.

[Geoff 555]

Hello Phil It has a Mw22-16 S/No N 10543. Struggling a bit now, not only dont I know what I'm doing so keep finding things that dont make any sense, but without a glimmer from the tube am not only daft but blind as well.

Cheers and ta.
Geoff 555

[Geoff 555]

PS. Phil yes I did find the 0.1 under the tag board but that is one of the things that dosnt make any sense , one end to tube side of the metrosil and the other side to chassis, if I've read things right except that it isnt to chassis?? see what I mean?
Cheers.
Geoff.

[Sean Williams]

try running the tube from a seperate 6.3v transformer, see how bright the heater is...

Might also be worth measuring the heater chain current, as it is easy to get the wrong tappings on the dropper...

[Geoff 555]

Hello Sean thanks for the reply I dont have a 6.3V transformer but the nearest was a 5V DC supply and it was quite bright. For the heater chain current I disconnected the green lead from the dropper, which was the only way I could think of doing it. It was 0.31 A (AC)
Green lead tag J
Red lead tag F
Mains supply 245V.
Cheers.
Geoff555.

[Sean Williams]

Ok, have you tried to measure the Heater Cathode resistance? - you can do this cold, and once again when it is hot (you need to run the tube to temperature, remove supply, and quickly measure the resistance)

I would be inclined to try running the set with the seperate heater supply - you will need to install a suitable resistance across the tube heater wiring - once you have done this you will be able to see if the tube has emmission problems - I would be very suprised if it was that flat!

Cheers
Sean

[Courtney Louise]

OK I am far from being an expert. Are you trying to get a raster with the Tuning panel still connected? Try disconnecting the HT feed to the lower deck incase there is something there pulling it down. You should be able to get a raster from the upper deck if all is ok. If your really stuck and you dont mind the travel I can have a look at it for you. I am in birmingham

Andi

[beery]

Hi Geoff,
can I ask some questions?
What type of meter are you using to measure the A1 voltage?
You will need a modern digital meter here as a moving coil meter will load the circuit too much.

Have you changed the 0.001uF and 0.003uF wax caps that go across the heater chain in the RF unit? If you have left them in place, see if they feel warm or look shiney. As a stop gap you can just cut them out of circuit at one end. Leaky caps here cause the tube heater to be dull and the timebase heaters to be extremely bright.

Also (though not normally a problem with the MW22-16) some Mullard tubes suffer from internal heater short half way along. Carefully tapping the tube neck with the back of a screwdriver whilst the set is on can sometimes clear this fault.

Cheers
Andy

[Geoff 555]

Gentlemen so much help and I cant thank you enough for your replies.
I will try my best to answer your questions as much as I am able. Sean measure heater cathode. (The new meter may be playing about as the reading on the 20M range takes some time to settle.) Cold 85Meg Hot 77Meg.
Andi (Jarl)I may well be paying you a visit if thats OK, it depends on the answers to a couple of questions.
Beery hello.All the caps have been changed but if necessary will check them all!! The meter is a DVM but I have a suspicion that all is not well, based on no more than a gut feeling,really. As regards tapping the tube,well , there is what I thought initially was a crack, that runs from the tube base to under the scan coils, it's deep enough to feel and stop my thumbnail from moving across it. So tapping it,umm no ta.


In an idle 5 minutes when I stopped because confusion was happening, I had a sudden horrible thought, have I actually got a 'hybrid' IE: a non matching main chassis and RF unit. I ask because I have never seen this set working and apart from it being in the family for many years, I dont know it's history. So far it's consumed over £300.00 and as such there is no light as yet, so could someone Please confirm what I have, I am not giving up, just need to know what I am getting in for.

Main chassis numbers. A6. 33840 round disc. 83 - 30759. (PZ,PL,ECL etc.)

RF unit. A22 28892. on disc.(EF and EB's)

Long post but I must get things clear.Thank you I await your comments etc.
Cheers.
Geoff 555.

[PJL]

I know nothing about tellies but this is as I understand it:
* 0.31A in the heater chain (OK)
* 3.1V AC across CRT heater? (should be 6.3V)
* Heater dim and much brighter when 5V DC applied

Which leaves two possibilities: something is bypassing the current (faulty capacitor or chain wiring error); CRT heater has internal short.

So next step is to break the CRT heater connection and measure the AC current at the back of the CRT...Peter

[Sean Williams]

Geoff,

Sounds like a normal TV22 to me.

Dont panic, or stress out yet - it will be a simple problem I am sure.

The resistance readings from the heater and cathode sound fine to me, so I would think the tube is ok

We need to find out why the tube heaters have such a low voltage across them.

I will dig my set out and have a look around it - perhaps I will get inspiration!

Cheers
Sean

[Heatercathodeshort]

The Mullard tubes are very prone to a partial short circuit in the heater. Its as simple as that. With the set working normally approximately 6.3v A.C. will appear across the heater pins when measured with any normal meter. A reading below this usually around 3v, will prove the shorted heater.
While the set is working, tip it back somewhat so that the neck is slanted backwards.
Note the brightness of the tube heater and gently tap the base of the tube. You may well see it brighten slightly and tiny hot debris fall from the cathode assembly.
When you have the heater glowing normally you should be able to adjust the ion trap and obtain a raster.This will only prove the point but will not be a permanent repair. It may last only a few minutes. This is common with all Mullard tubes from the MW22-16 right through to the AW43-80 some eight years later. Its not as such a common fault as Mullard tubes are very reliable but the partial shorted heater was the way most of them failed usually after many years use. Regards, John.

[Station X]

That sounds reasonable. Half the volts across half the heater means half the power so the intact half of the heater will survive.

However Geoff says he's powered the heater from a 6.3V supply. That means twice the volts across half the heater or half the resistance. That would be a 4 fold increase in power. Would the heater survive that?

[Heatercathodeshort]

It certainly would survive that. As a lad that heater fault occurred on a Mullard MW43-64 tube fitted in our family Ferguson 236T. I was only 12 at the time working in a television shop after school. I fitted a crt transformer and the heater lit like a torch bulb. It continued like that for over a year before finally going O/C! I fitted a second hand tube provided by my generous employer and returned the set to full use.
The whole heater remains INTACT. One half of it shorts out due to the insulating coating wearing away where the 'M' is formed by the tightly packed filament assembly. This produces the effect of a .6amp load to the series heaters and results in a very much reduced voltage drop. Happy Days! John.

[Station X]

Does anyone know the resistance of the heater? 6.3V at 300mA equals 21 ohms. That's with the heater hot of course.

[Geoff 555]

Hi all. OK measured the current without the heater 0.3 Amp and with the heater 0.31 . I have tried the lean back and tap method, just bouncing a rubber handled screwdriver on the tube. 3 tiny silver globules of something in the neck, but no change. Seems that a shorted heater could be the answer.
Andi (Jarl) has suggested breaking the HT to the RF section as a try, so how do you do that please? As a last try before calling it a day with the tube,I confess that I am convinced it's duff, cut the HT to the RF section and give the tube some volts whether it likes it or not, theres nothing to lose.
Thank you once again.

Best wishes
Geoff 555.

Apologies, not so much stressed as limited as to how much I can do, money wise a bit but mostly physical, 10 minutes at a time and then having to stop but that is how it is,

[Heatercathodeshort]

Hello Geoff,
The series heater chain current is .3amp. Say for instance a .6 amp valve is inserted in the chain. [The voltage is not that ctritcal] The total current flowing remains at .3amp but the voltage across the .6amp heater will be HALF of what it should be because only .3amp is flowing through it. Likewise if a .15amp valve were inserted the chain current would again be .3amp but the .15amp valve would be passing TWICE the current and would therefore have twice the voltage across its heater.
When the CRT heater develops a short it appears like a .6amp load and passes HALF the voltage hence its dim appearance. The total current of the chain remains at the nominal .3amp regardless. Its Ohms law and never changes. I think your tube is U/S unfortunately and I wish I had read this thread earlier to save you all this hassle. If your ever around West Sussex way please feel free to give me a call and I will demonstrate this for you. Regards, John.