Ekco TC267/1

[acottrell]

Hi Guys
I have recently purchased this set and it is totally untouched.
When switching it on using a variac in the VHF radio position the valves lit up and I had sound. Winding the variac up I had a burning smell and smoke then it went completely dead.
Taking the chassis out top side looks like two thyristors towards the front under the dropper by the HT cap. The one has completely burnt out . I have now replaced the wax capacitors in the set and replaced what I think is the remains of a thysistor with a wire wound 75ohm resistor . Switching the set on the resistor gets very hot straight away and starts smoking again. I know there will be a short any ideas where to look? I don't have a circuit diagram for this set which doesn't really help me.
Thanks

[nigelr2000]

I think the thyristor is a top hat diode looking at the diagram from the 1957/58 RTVS book, just done a quick scan of the main diagram there are others covering the IF and tuning parts. If you replaced the "thyristor" with a resistor I doubt the main smoothing electrolytics were happy about it !!

[Heatercathodeshort]

Having replaced all the wax capacitors without reference to a circuit, you may have generated a few problems. There are also capacitors in this model that look like resistors.
The original metal rectifier in Ekco receivers is manufactured by Automat. It is extremely reliable and if the 'thyristor' is in fact a diode, it may have been upgraded for no good reason. Please post some pictures.
Before going any further I would suggest you check the physical condition of the line output transformer 'plastic' case. They tend to break down giving off a sickly sweet smell. If it appears to be breaking down a new case can be fabricated from Paxolin sheet.
Many articles dealing with Ekco receivers have appeared on this Forum covering the 200 and 300 series chassis that have many similarities and fault symptoms. John.

[FERNSEH]

Ekco TC267/1: Is this the later version of the original TC267 which employs a single 0.3amp heater chain instead of the separate 0.1 and 0.2amp chains?

DFWB.

[acottrell]

Hi Guys
Thanks for your replies. Will post some pics tomorrow . The wax caps I have changed were all normal wax caps 0.1uf x5 350v working and one 0.5 boost capacitor so no worries with that. Also two 0.01uf caps.
Interesting about the diode. It was so far burnt and reduced to charcoal Hope I haven't caused more damage now with the resistor in its place!
The line output transformer physically looks like new under the dust. In fact the chassis has no rust on it so I am hopeful it might be ok.

[acottrell]

Hi Guys
please see pics hope this might help. The white resistor is what I put in place of the diode. Cant take a photo of the diode as it really had turned to dust just the two legs left!!
Thanks
Ade

[beery]

Hi Ade,

It seems it was actually a resistor, R120 on the trader sheet, the value is 51 ohms and it is in series with the heater chain, between the large thermistor (the dark grey rod near it in the photo) and the heater tap changing lead.

Cheers
Andy

[beery]

Hi again Ade,

I also notice from your photos that you have not replaced the brown Hunts caps. These are the ones with the red or white paper labels. They look like nice modern plastic things, but in reality they are waxies on the inside and very unreliable.

If you have smoke so soon after switch on you could have a short in a 0.001uF heater decoupling capacitor.
To check for short across the heater chain use a meter on ohms range with the set unplugged from the mains. Unplug the CRT and measure between the chassis and the heater chain. If you find a shorted 0.001uF cap then you can simply snip it out for the moment and replace it later, however if one has failed then others will follow in the first few hours of operation.
Be sure to remember to plug the CRT back in before you power up the set.

Cheers
Andy

[SteveCG]

Ade,

Could you oblige with a close up of the voltage selector panel which is in photo no.3 of post no.6 please?

It looks suitably complicated for the AC/DC era !!

[acottrell]

Hi Guys
Thanks so much for your responses. Interesting about the small hunts caps didn't know that. I will check for shorts as you have said across the heater
Thank you

Will keep you posted.
Will also get a close up pic of number three photo
Ade

[acottrell]

Hi Andy
Just quickly put I meter between heater and chassis and you are right I have a dead short! will follow the heater trail find the shorted cap
Will let you know how it goes not able to look at in now for a few days

Steve here are some close up pics

[HamishBoxer]

Dont check small brown Hunts capacitors just change on sight.

If they read ok remember they breakdown under load more often than not.

[acottrell]

Thanks Guys
I have learned something today. Will find the shorted cap out of interest and then replace all the brown hunts ones.
Thanks
Ade

[Freya]

Originally Posted by beery

It seems it was actually a resistor, R120 on the trader sheet, the value is 51 ohms and it is in series with the heater chain, between the large thermistor (the dark grey rod near it in the photo) and the heater tap changing lead.

Hi Andy,

That value is only if the set is a T293. The T267/1 the resistor is 29 ohms
I have marked the positions of the 0.001uF decouplers in the heater chain.

[acottrell]

Thanks.
Need to change my 75ohm now.

[Freya]

These snippets from the genuine Ekco T267/1 may help, zoom with keys ctrl and +

[beery]

Hi Stephen,
thanks for clarifying the value from the original Ekco manual. Trader sheet 1278 is very confusing on this point and indeed shows the 29ohm as only applicable for the T293 which is clearly a mistake as it should have stated also for the TC267/1.
Sorry about that one.

Ade. It is interesting to note that the lower value is because your set inlcludes an extra valve for the spot wobble circuit which is something I have only read about. It will be interesting to observe the effect on the picture when you have the set working.

Andy

[dazzlevision]

Originally Posted by beery

Ade. It is interesting to note that the lower value is because your set inlcludes an extra valve for the spot wobble circuit which is something I have only read about. It will be interesting to observe the effect on the picture when you have the set working.

Hello,

I had an Ekco TC267/1 in the late 1960s and I recently restored a TC267, which also has spot wobble. The Spot Wobble does actually do a good job of diffusing the line structure when switched in.

Regards,

Dazzlevision

[acottrell]

Thanks Andy/Guys
Looking forward to getting this set working. I will order myself a 29ohm or nearest value resistor while changing the hunts caps I hope once the caps are done the lopt and tube will be ok. The lopt physically looks really good, fingers crossed!
Thanks again for your help guys still have a lot to learn but seem to struggle my way through restoring my collection of radios and tvs thanks to your help and advise and this forum!
Ade

[Freya]

To avoid mistakes in the very tight areas of the RF/IF strip I recommend just doing the decouplers first, get a raster up then work through doing a few at a time monitoring the output with test card up.
Its a good idea to pass some current through the overwind on the lopt, this drives out any moisture and you get the full EHT, to do this you need a 1 amp bench power supply with about 24 volts. Leave it connected for 12 hours ideally. (it gets hot but not enough to melt the wax off)