Philips T-Vette

[Kat Manton]

Hi,

...it seems my original thread has been hi-jacked... still, it means there's a lot of fault-finding info for this set ending up neatly in the same thread, one for the archive later.

Anyway, since I've ended up nocturnal again and the neighbours wouldn't appreciate me attacking cars with angle-grinder and MIG set at 2am, I've revisited some of the items lying around in bits.

So, a progress report on my T-Vette... I took the case off and found some crumbly debris inside, a bit of detective work determined this to be the remains of thermistor R4118. As it's across a 3R3 resistor (R4134), I'll give the set a try without it; I'll try it on a 12V supply first before I go so far as to attempt to run it off mains - and I'll have the CRT disconnected until the health of the 11V regulator is proven.

First, I need to restock on fuses, one of them was absent, a bit of wire was found wrapped around the tags instead. Once the set appears to show signs of life, I'll ignore any problems with field size/linearity until I've sourced a replacement for this thermistor.

Any ideas on replacements?

Cheers, Kat

[dazzlevision]

Hello,

The thermistor is a Mullard/Philips type VA1077 - quite widely used in transistor circuitry of this era.

It is of rectangular shape with three coloured bands - from the leads end: orange:red:black. There is brief data of it in the Mullard pocket data books of that era.

Regards,

Dazzlevision

[TNC]

Well I finally got to "Can-A" and was able to see a problem cap. - C 2073 (5.6pf) which actually looked "cooked" - although at such low voltages I can't really see how it can have been affected in that way.
Anyway, it measured less than 500 ohms on my Avo 7 so out it went. Since taking the trouble to remove Can-A, I thought it worthwhile to check all the other caps. and spent a happy hour with the solder-braid lifting legs and actually removing one of the coils to get at a cluster of caps. They were all fine and looked new - distinctly different to C 2073 which I now replaced with a new cap from Farnells,
Re-fitting the can requires three hands - one to hold the can against the pcb, one to hold the soldering iron and one to feed the solder - it's more difficult with two!...but well worth the trouble when the result is a really cracking Test Card C - in either 405 or 625.
A quick tweak on the linearity and height, final re-set on the 11v rail (creeps up by about .25v in the 15 minutes from switch-on) and that's it. Just left to clean the case and re-assemble.
Should I have checked Cans B &C - well maybe but the performance is so good I decided to let sleeping dogs lie!
So that's one more done!

Many thanks -to all for helpful input (esp. Dazzlevision)...hope you get your one sorted Kat.
Trevor.

[Mersey_Swimmer]

Originally Posted by ppppenguin

This is nothing like the AF114-7 series as it's a video output transistor which can withstand relatively high voltages while still having good HF response. That was a difficult trick way back then. Probably liable to tin whiskers and not so easy to substitute.

The AF118 does belong to the same group of transistors, but presumably specially selected during production for their 70v Vc max (the 114-117 are all 32v max). I've got a few NOS AF118s and can confirm they suffer from the same pathology as their lower-voltage brethren.

Equivalents are listed as AFY19 and 2N1017 Type AF128 is not at all suitable as its Vc max is only 9v.

Pete