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What to do with a Philips T-vette...

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Lloyd
(@lloyd)
Noble V-Ratter Registered

...With a duff tube!

The CRT in this nice little set has finally decided enough is enough, and the heater has gone O/C. Back in 2005 when I got this set the tube heater was O/C but I managed to 'weld' it with high voltage from one of those little CCFL inverters that were available from Maplin for not very much, it then gave a pretty good picture, and continued to do so until yesterday! I did try the same again, but this time using my Ekco TMB272 as my source of high voltage. It didn't work! I thought it had at one point when the Ekco's line stage sounded strained, and the heater in the T-vette's tube started to glow, but there was still no continuity afterwards.

So what to do? use it as a doorstop? Probably all it's good for now! I know I'll never find a correct replacement tube, and of course it's an odd size. I have a 9" tube that I'd bought to replace the nearly dead one in my JVC Videosphere that I haven't used yet, maybe some sort of mask to hide the gaping hole around it, and some brackets to mount it?! That could work, although it'll look very odd! There is a CRT on some sort of monitor chassis on ebay, looks about the right size, just need to ask the seller to measure it for me! Any replacement tube is going to probably have a 6.3v 300ma heater, which will be better long term as it's less likely to just give up for the fun of it, but it'll require some messing about with the CRT heater supply.

Does anyone know of any more common sets with a tube of the same, or at least very close to the same size as these? roughly measuring the CRT hole in the cabinet, it's about 10 and a half inches, so the tube must have been 11", I'm pretty sure I can't squeeze a 12" in there, which is a shame since they are more common! A 10" tube might be OK with a bit of something round the edge, were there any black and white tubes made to 10"?

Regards,
Lloyd.

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Topic starter Posted : 12/04/2016 8:21 pm
PYE625
(@pye625)
Famed V-Ratter Registered

I believe there is a T-vette on e-bay at the moment :qq1

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Posted : 12/04/2016 9:04 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

I saw that one :bba

Very tempting, but then I'd end up with another one to play with! Or knowing my luck, that one will have a duff tube as well :bbd

Regards,
Lloyd.

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Topic starter Posted : 12/04/2016 9:16 pm
crustytv
(@crustytv)
Vrat Founder Admin

Well you can always.............. :aah

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Posted : 12/04/2016 9:20 pm
Rebel Rafter
(@rebel-rafter)
Active V-Ratter Registered

Hi, Lloyd, RR here, I have the same problem. I also have a little T-Vette with a tube full of air! It's got a brand new gun and I never got to use it as I recently set about repairing a simple sync. fault and I had to remove the tube socket to get the board out and when I tried to put the socket back on the little tube one of the pins somehow got bent and it cracked the glass. How absolutely rotten is that! But Chelmer valve have got a suitable tube but it's a bit pricey at about £75 including vat and postage, it was a bit too pricey for me unfortunately and I also missed a Sanyo set on ebay that had a similar tube. I can't remember the model number but it had the number 11 in the number and it was almost definitely 11"and 90 degrees just like the T-Vette tube and the set was battery/mains so the tube would almost definitely be the narrow neck type but try finding another one close enough to home, I've found odd similar sets on ebay but they're always far too far away for me to collect them. There is another T-Vette on ebay at the moment but I can't remember where it is in the country and of course there's no guarantee the tube would be any good. RR.

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Posted : 12/04/2016 9:21 pm
crustytv
(@crustytv)
Vrat Founder Admin

On a more serious note I repaired one of these a couple of years ago. The advice I followed at the time with a set of unknown state is to not just power it up as this could be a short journey to the scrappers. The AD149 can fail s/c and thereby send the 11V rail high enough to blow the CRT heater.

I removed and tested the AD149 prior to powering up, then when I did, I powered with the CRT base disconnected whilst monitoring the 11V rail which can be adjusted by a preset.

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Posted : 12/04/2016 9:33 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

:aak
Thanks Chris! Actually, it looks quite good with fish in it...! I did have a print-out of test card F somewhere, that I used to stick over the screen of some sets, maybe I'll have to find it and put it on this one!

Hi RR, That's awful! I nearly lost a tube in a small Hitachi portable once, because silly me thought it'd be a good idea to take it apart on my workshop chair, I had the front half of the set including CRT on the seat, and balanced the rear cover on the back of the chair. I knocked the rear cover off and it bounced off the base of the tube, I thought it'd be knackered at that point, but it had just bent the pins. I started carefully straightening them when all of a sudden there was a ping and a piece of glass shot off the base next to one of the pins! What was surprising was that it hadn't gone all the way through to inside the tube, so the tube still survives even now! I do wonder if it will eventually give up with heating and cooling, but so far (touch wood..) it's OK. I'll keep the little Sanyo sets in mind. The other T-vette on ebay currently is located in Essex.

Regards,
Lloyd.

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Topic starter Posted : 12/04/2016 9:46 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

I did wonder about the LT rail going high, this set had been suffering from some voltage fluctuations, sometimes the picture would shrink down to a 4" square then come back again. Someone has previously replaced the adjustment pot for a rather large wirewound pot at some point in the set's life, it's not brilliant, but the LT rail can be set with it to 11v, I had a play with it today, not that there was much point, but the LT was sitting at 10.8v. If only I could just take it along to the re-gunners and get a new gun for not very much... Not much chance of that happening these days!!

Regards,
Lloyd.

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Topic starter Posted : 12/04/2016 9:53 pm
TVJON74
(@tvjon74)
Honorable V-Ratter Registered

Hi all,
I remember some time ago and I can't remember by who or when, but a mod was devised to blow a fuse if the heater volts went skywards due to the regulator transistor going s/c. I think it involved a zener diode and a maybe a suitable series resistor across the heater supply, but I might be completely wrong!

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Posted : 12/04/2016 9:57 pm
Rebel Rafter
(@rebel-rafter)
Active V-Ratter Registered

Hi from RR. I know that circuit for over voltage protection. you can find a suitable one in "television" magazine june 1982, it was actually devised for protecting an old Betamax VCR but it can just as easily protect a little 11 volt tube heater. I couldn't agree more about not powering up any T-Vettes that you find, and the same goes for almost any old battery/mains black and white portables out there with bog standard power supply design, there are exceptions of course like the Indesit T12EGB which I seem to remember had a rather unusual design to say the least but that's another subject, and I know where there is one of those in a loft... And I have a friend who goes round loads of car boot sales and I've given him some detailed notes on how to spot an 11" set with even a cardboard screen template! And I've made the most important note of all in his instructions NOT to power up any he might find along with details of why. RR.

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Posted : 12/04/2016 10:43 pm
AidanLunn
(@aidanlunn)
Member Deactivated Account

I have two of these, a partially working Stella-branded set and a completely non-working Philips.

So your set may come in useful for spares Lloyd, either for yourself or for others

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Posted : 15/04/2016 3:50 pm
Terry
(@terrykc)
Famed V-Ratter Rest in Peace

Hi all,
I remember some time ago and I can't remember by who or when, but a mod was devised to blow a fuse if the heater volts went skywards due to the regulator transistor going s/c. I think it involved a zener diode and a maybe a suitable series resistor across the heater supply, but I might be completely wrong!

All it needs is a fuse in series with the heater supply and a suitably rated zener across the supply on the CRT side of the fuse.

If the voltage goes high, the zener conducts, both protecting the tube and blowing the fuse. Simples!

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Posted : 15/04/2016 4:06 pm
slidertogrid
(@slidertogrid)
Reputable V-Ratter Registered

Hi Lloyd
I think may have a spare CRT for a T-vette (somewhere :ccg ) I'll have a look over the weekend and let you know.
Rich.

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Posted : 15/04/2016 7:42 pm
slidertogrid
(@slidertogrid)
Reputable V-Ratter Registered

Hi, I have found the tube. The emission is good. There are a 3 very small shallow scratches right in the middle of the screen, they may well polish out with patience. ( other glass polishes are available.. :bba ) They are very shallow and only visible with daylight directly on the screen. I doubt you would see them when the set is working.
Let me know if it's of interest and I will remove it from the scrap set.
Regards,
Rich.

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Posted : 16/04/2016 4:18 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

Hi Rich,

That would be fantastic, thanks! A few scratches are nothing to worry about. Please let me know what you would like for it!

I'll look after this one better, firstly by re-vamping the PSU, and fitting the zener mod, I've heard of that mod before, seems like a very good idea to me. I've also just this week got myself a little Perdio Portorama (is that how it's spelt?) which also has a tube with 0.06A heater at 11 point something volts, so that could probably do with the same modification, I've only powered it from a bench PSU so far, limited to 11V.

Regards,
Lloyd.

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Topic starter Posted : 16/04/2016 8:14 pm
slidertogrid
(@slidertogrid)
Reputable V-Ratter Registered

Hi Ok I will get the tube out tomorrow. Do you want to collect from Peterborough? If you are not in a particular hurry I can probably get it to Boston as I have to take a clock to a shop there for repair in the next few weeks.
I recon it may be a bit dodgy to post apart from the cost.
Is £10 Ok ? (I paid a fair bit more than that for the set but have used a few parts from it myself).
Probably best if we arrange by P.M?
Regards
Rich.

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Posted : 16/04/2016 11:18 pm
Lloyd
(@lloyd)
Noble V-Ratter Registered

It's been a while since this set expired! I'd actually forgotten about it until a couple of weeks back when Rich sent me a PM asking if I was still looking for a tube, as he had one from a scrapper! I went and collected the tube  last weekend (many thanks again Rich!) and set about pulling the set apart to check it over and get it ready for it's transplant.

I remember there were a few faults present when it did work, the sudden shrinking of the picture to about 3" square was one, which probably accounted for the demise of the old CRT. The pot for setting the 11V rail had been replaced sometime in the past with a rather large wirewound pot! It was also badly fitted, soldered to stubs of stiff wire inserted into the PCB, one connection had actually broken, so I decided to replace the pot with a new preset, and fit it a bit better. The new one was very much smaller, so I ended up drilling the PCB to accommodate it.

Whilst I was in there I thought it'd be a good idea to check and replace any resistors in the regulator circuit, The first one I looked at was R4049, a 10 ohm one right near the edge of the board, one leg had a duff joint, and the resistor read high too, so i replaced it, and a couple of others.

I finally came to show the set some power, minus the CRT! All seemed well, but the system switch wasn't happy, especially on 405 lines, so that was taken out and cleaned up, one of the springy contacts was a bit out of shape, and the fixed contacts were scored and blackened, I cleaned them up, and swapped the loose springy contact with another from the other end of the switch and re-tensioned it. Checking with a meter showed the contact resistance was now around 0-1 ohm, whereas before I was getting anything between 4-20 ohms! The set was much happier with the newly cleaned up switch.

Now back to testing, I have the multimeter hooked up to the 11v line, and a small bulb connected where the CRT heater would be, at first I was able to set the 11V line nicely, but the longer the set is on, the more it creeps up, getting to 11.6V, I have found that the AC128 transistor is getting hot, and heatsinking it with a croc clip is bringing the voltage back down again, so I think I need to find out why this is happening. It's worse on 405 lines than it is on 625, where the lowest you can set the 11V line to is 11.3V!

I've taken out the AC128 and bunged it on the Chinese component tester, where it told me it was some sort of P-MOS (or something like that!), and it doesn't seem to be shorted at all. Not sure where to go from here!

Regards,

Lloyd

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Topic starter Posted : 23/10/2021 6:27 pm
Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator

I'd swap that AC128, if it were mine! - I'm also wondering if it's possible to 'crowbar' the 11V with a decent zener diode to prevent any future over-volt incidents.  I may be talking nonsense, but I'd be happier if the 11v supply can be clamped, one way or another.

Do you know why the picture shrank?  If not, I'd probably want to investigate that before doing much else. My guess is that the HT rail has been pulled down by a faulty component.  The trouble is, unless you have some expected voltages to look for, the only visual guide is to have the CRT installed while testing, so everything needs to be doing exactly what it's supposed to - We don't want any nasty surprises to take out your replacement CRT.

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Posted : 23/10/2021 6:44 pm
Lloyd liked
sideband
(@sideband)
Famed V-Ratter Moderator

You should be able to get the supply down to below 10V when it's working. Mine is set to 10.8V. Check the zener (think it's an OAZ202). I've got a scrap rear panel from my own set that has a broken corner where the contrast pot was). I've since replaced it with a good panel supplied by a forum member. However it is minus the set LT pot (which is now on the replacement panel). You are welcome to it for parts only (since that is all it is fit for). You could look at the thread I wrote up for mine (I'll find the thread and link it here). I had a few supply problems with mine one of which was a leaky AD149. Worth checking all those old germaniums in the PSU now. I do know that the ones on the spares panel are good.

Don't reconnect the CRT base until you have that supply down to around 10.8volts

 

Here's the link to the story of mine. The last page covers the transplant of the replacement PSU/frame/sync rear panel.

Philips TVette (11TG190AT) – Black & White Television – VRAT Forum (radios-tv.co.uk)

 

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Posted : 23/10/2021 6:50 pm
Katie Bush and Lloyd liked
Lloyd
(@lloyd)
Noble V-Ratter Registered

Cheers for the replies!

I'm fairly confident the picture shrinking was a by product of the loose connection to the 10 ohm resistor, and also possibly the duff joint on the adjustment pot, as it would come and go with giving the cabinet a rattle! Rich also gave me a 12V zener diode to make up a crowbar, which I have yet to implement, just nee to find a suitable place to stick it across the 11V rail, with a fuse before it to disconnect the CRT in the event of the voltage rising.

Interestingly, I now have the set on mains (I was on 12v before, I've lost the mains lead!) using a death trap croc clip lead arrangement, and an isolating TX, and I'm able to set the LT to 10.8V on both standards, the AC128 is still heating up, and the volts are rising. I've done some voltage measurements on the AC128 and they are as follows; C=0.63V, B=16.15, E=16.28.

I think I've got another AC128 somewhere, but if not I'll drop you a PM!

Regards,

Lloyd

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Topic starter Posted : 23/10/2021 7:27 pm
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