GEC BT1156 First Light & Vidor CN4216

[oldticktock]

Morning Steve, errrr evening

Tell me about it with regards to the tuner valves!

This set is a greedy it's taken all the valves I got from Malc and then some, lucky I had the spares. The only original valves left are V5,V7,V10 & V13. I've a good mind to just give it all new and be done with it, however I only have EB91's for V7 & V11 I don't have any more 30F5's or 30P12's left.

Trevor,
Thanks for the tip so as per my pic?

As for the Diode in series resistor would a 10R or 33R be better, it's not going to kill more valves is it? will be stuck then.

[GrimJosef]

Originally Posted by oldticktock

The GEC & Vidor arrived after being dropped off by Grimjosef, nice fella.

Decided to do what everyone seems to do and select one for plug-in.

The Vidor has a lot of wires chassis interconnects removed and the EHT unplugged so someones been at it. Not confident of this one.

GEC looked tidy so that was selected, so found my rubber pants, a broom handle and powered on.

Thats what i got, not much wrong with this then.

Hi Chris,

I thought I'd give it a week then ask if you'd had a chance to get them out of their boxes. But it looks like I'm a couple of hundred posts too late

Good to see that they're keeping you busy though ! By the way, thanks for the chocs. They're going down very well (literally) with SWMBO. And the bottles were very welcome too, if way too generous !

Cheers,

GJ

[oldticktock]

Hi GJ,

The GEC ws out of the box and on the bench the same day glad you enjoyed the goodies and it was a pleasure to meet you and the boss

Chris

[G8KBG Tony]

Assuming the correct value dropper sections have been fitted, the photos on post #138 show the voltage is set to 220v. Could account for the valve failures…

[oldticktock]

Ahh, I left where they were when I received it, I was not sure what how to set for 240

the two RS dropper sections are 66R which must be R136 & R139
the Blue ceramic is 82R
the silver/grey is 1.2k

One of the 66R is duff, the other reads ok, the ceramic reads 85R and the silver/grey is not on circuit...... Oh dear more bodging to unravel.......not another!

[G8KBG Tony]

The silver/grey item is a thermister - R133 on the circuit diagram. I can't reliably advise on the rest of the dropper from the photos, so I'll have to leave that to you to work out.

[murphyv310]

Hi
Things have been happening! I see there may be an issue with the mains tapping and dropper values. Now although we have a nominal mains of 230v, guaranteed it never is!
All my sets are set to 240v, so lets assume thats where we want to go. All we need to do is to add up the dropper resistors that are in circuit for 240v and then check that is what we have.
Tony is quite correct in saying that the wrong tapping could cause a valve to fail, it's really like asking a 60 year old man that sits at a desk all day to run a marathon!
Chris there are so many tips that I and many others use it would take an age to tell you and sometimes even remember in giving these old sets the kiss of life. One thing I do is to run the set at 220 actual volts (tv set to 240v) for a day or two before going to full mains, for some reason it "runs in" the TV and all seems fine after. To much HT or heaters can be sore on the set, and will often show up whats weak anyway possibly not a bad thing though, but like you I like to conserve my valve stock!

[oldticktock]

I need to replace a 66R section as its only ready 1.2R the other sections are ok.

I've made a map of the wiring so as to be certain and serve as a reference point, I'm too tired to continue now so will leave it for now.

Chris

[oldticktock]

Originally Posted by murphyv310

Regarding your comment "I wont be beaten" Please never get cockey, everyone will be beaten sometimes! You wouldn't be asking all these questions if you knew it all!!

Only just noticed this comment, Trevor it was meant in a tongue in cheek humour way, you know a Basil Fawlty moment, whacking the GEC with the probes whilst shouting " I won't be beaten you swine" makes me you thought otherwise it was not meant in anyway to be cocky. Please lets not miss judge

Chris

[VideoJunkyard]

Have you read the 'blue' RS 66R section with the voltage selector removed? Looking at your diagram it is blatantly obvious that the section is shorted out by the links - hence it reading low!!
Remove all the voltage selector links and read the dropper again - droppers never (to my knowledge) go faulty low resistance - usually O/C. It may be open which is why the set is configured for 220v - but at this point you won't know.

[Techman]

Hi Chris,

Just a few thoughts on this set - BTW, it isn't the same as one that I used to have many years ago, mine was the model before with the flat wired chassis & not the PCB version.

On off switches that haven't been in use for a long time tend to get 'resistance' in the contacts. I find that they can have up to 50 ohms reading across the contacts when they should have zero. For this reason, I've found it best to by pass the switch until everything else is up & running & then work the switch as said before with some contact cleaner until the resistance goes down. The possible resistance in your switch could have been causing the lower voltages, although I would have thought it would have started to burn out by now if it had - but you never know.

The other thing that I would have done after replacing the rectifier diode & series resistor, would have been to clip a test meter onto the HT & wind the set up on a variac while continually monitoring the HT voltage. Then with all valves warmed up & conducting I would set the HT to the 'book' voltage with the variac & then look to see what my mains input (out of the variac & making sure NOT to go above normal mains) was. If my HT voltage was still too low with an input of 240 volts, then I would lower the value of my series resistor & try again until I got the correct voltage. If it was still not possible to obtain the correct HT voltage in this way, then this would indicate some other fault causing too much current drain. Doing it this way would have avoided the problems you had earlier. If you found that regardless of reducing the series resistor you were still not getting any more HT than with the old metal rectifier, then you may as well go back to the original blue metal rec.

Now for some possibly bad news - turning the dropper down to a lower mains tapping was a very common practice used by 'old time' TV engineers to get a last few months out of a failing tube. It would be turned down to 220 volts & often down to 200 volts. Sets would run for quite a while like this, even up to a year or more with out valve failure, but when their time came, that would be the end for the TV & time to smash the neck off the tube with a hammer & skip it.

So you may find that the set won't want to run too well when you set the mains tapping back to the correct voltage. On the other hand, you've changed all the valves that would have gone low emission from being over run & it's only likely to be the tube that has suffered & it probably wasn't that good anyway, therefore the reason for the dropper being turned down in the first place. I could be wrong & the previous owner turned the tapping down due to an open circuit dropper section & it hasn't been run for too long like that. If the tube is a bit low, then you could run the heater from a separate heater transformer, say 7.5 volts to give it a little electrical 'kick' in the teeth...it's not as if it's going to be on all day & every day like it would have been when it was 'newer'.

So just a few thoughts. You may find it'll all come right, but best to be aware of what you might find if it does turn out that the dropper has been wound down to 220 volts back in the 60s when the tube started to go flat. Having said that , it is only set on 220 volts & NOT 200 volts like a lot of them were when they were one step away from the tip - back in the day

Good luck with it.....can't wait for that Vidor

[Techman]

Just skipping round the threads & coming back to this one again...it may not be as bad as we think. Looking at previous pictures of the dropper - as has been pointed out by others...sections have been bridged by those wonderful 'RS' round dropper sections. It could be that the engineer that did the work may have had too high a value in stock, so turned the mains tapping down to compensate.

I think someone has already said to measure the total resistance of the dropper 'as is' with the mains selector left in the 220 volt position....then go from there.

[murphyv310]

Hello Chris
I was just thinking you have a 30P19 in your set as a line o/p valve, Is the correct equivalent not a PL36? one valve is a beam tetrode and the other a pentode!
Although they can be swapped often you see a difference in width and EHT.

[FERNSEH]

Hi Trevor,
Original line output valve used in this set was the GEC N308 which is equivalent to the Mazda 30P4. All the valves used in this set were sourced from Mazda. The 30P19 is the successor to the 30P4. The PL36 will certainly work OK but there is a possibilty that there will be internal connections on pins 3 and 6. Best check the PCB for any connections to those pins.

DFWB.

[DangerMan]

Hi Chris,
Techman sums it up when he describes why sets are often on the wrong mains tap, and what it does to the set.
Another reason the practice was common was failing selenium rectifiers. It brought the HT back up and gave a full picture... for a while.
Sounds familiar ?
Pete

[MALC SCOTT]

Hi Chris, what valves do you need?

[oldticktock]

Hi Malc

2x30F5
1x30P12

One of the 30F5 NOS had a busted pin.

I have EB91's

Kind Regards
Chris

[murphyv310]

Originally Posted by FERNSEH

Hi Trevor,
Original line output valve used in this set was the GEC N308 which is equivalent to the Mazda 30P4. All the valves used in this set were sourced from Mazda. The 30P19 is the successor to the 30P4. The PL36 will certainly work OK but there is a possibilty that there will be internal connections on pins 3 and 6. Best check the PCB for any connections to those pins.

DFWB.

David.
You are correct of course, Twas too early in the morning for my heed to be working

[oldticktock]

Hi guys, an update on where i'm at.

The on/off/volume switch is now working as it should, thanks for the WD40 tip.

I replaced the U25 with a NOS Mullard.

As recommended I replaced the U25 heater resistor as the one I used may have caused some corona and arcing at a later date.

Thanks for the information Techman, I do hope it's not what you fear but the probabilty is there.

I have measured the dropper with all selector plugs removed, the total is 276R, with it set to 220, the value is 178R and finally set to 240 the value is 249R, this is where it is now. With the HT measuring at 172V about 33V down if I'm right that HT should be 205V.

For the second time I clipped in the IN4007 with a series surge resistor value of 47R, I had the meter attached to monitor the Voltage. I had the variac down at about 120V (this is not precise it may have been more) powered on and I observed the the initial voltage just over 300V but dying back quick soon thereafter, I juggled the variac trying to set 205V for HT which I did but the mains was about 150V.

To cut a long story short I tried two other resistors, a 33R and a 10R, without success. Thinking I could be causing more harm than good, I decided to put the old metal rectifier back in circuit. I did this but the set was now dead, here we go again. This time instead of the two tuner valves dying it was the 1Amp fuse.

I understand that the silicon has a lower forward voltage drop than the old metal but should it not be ok with what I did, any clues as to where i'm going or what I'm doing wrong. I have read a bit more on the matter and I noticed that others have put a cap in parallel around the silicon (see pic) would this help?



All the best
Chris

[murphyv310]

Good Morning Chris.
What you did was 100% OK, the cap across the silicon diode isn't necessary at this stage. You will get a higher surge with a silicon diode than with a metal reccy, the set remember was designed around a metal reccy, fitting the 47 ohm slows down the charging time of the smoothers, but the charged voltage will always be higher until the heaters let the valves conduct and the load appears on the ht line. I do think your metal reccy has had its day so I would fit the IN4007 as a permanent fitting, I also would make sure the smoothers have a 300v or more surge voltage and if necessary replace them. You could wind the set up again on the variac but remember on the old days in the field when we fitted 100's of BY100's and 47ohm surge limiters there were no variacs to wind them up with.
Good Luck