Working on a set with a shorted G1 per the sencore CR-70 (no control over brightness fixed and too much brightness).

I followed the directions, checked after each try, max of 3 tries, no improvement.

Any tips? Its a very nice set (this is the one near Disney that TVdude1 was asking for someone in the area to check on.

its a 21CEP4. the set is MINT!! older RCA upright, did not not the model but looks just like a mini version of my CTC-9

Must be a bad short, try a tester with a higher power short clearing function. Or discharge a 3000uf 150v cap through it.

I was thinking about something like that but afraid it may burn a connector (of course the tube no use now anyway). I was going to try it again, but this time with the face of the tube down and tapping the neck as I hit the button. I was getting a good arc so something was happening, but it did not clear on the 1s few trys. I do not have the set currently but the owner said he would bring it back so I can try again.

The CR70 is known for being gentle, that's why you should try one that's not. The B&K testers seem to have a cap discharge short clearing function, do you have one of those? I can't remember the value of the cap in my 466, but it was around 400 volts I know that much.

I think I have a 440 somewhere out in the garage, stopped using it when I got the Sencore

You have nothing to lose really, the tube doesn't work anyway.

Got the 440 out, checked the caps, had an old partially shorted 5mf 250v, replaced that, used it to check some of my tubes seems to be working, so will use in on the 21CEP4 when it comes back in to the shop.

I have a fairly good book on this. Ill have to read up on it. My question is what is g1 shorted to? G2 or the Cathode? I would hate to blow that little think cathode wire open. From what you told me about the set I bet it was a factory defect and a customer return.
Maybe you could ask Timmy if he has any tips on clearing the shorts...?

routine short cleaning maint 101 :yes:

I have a fairly good book on this. Ill have to read up on it. My question is what is g1 shorted to? G2 or the Cathode? I would hate to blow that little think cathode wire open. From what you told me about the set I bet it was a factory defect and a customer return.
Maybe you could ask Timmy if he has any tips on clearing the shorts...?

Cathode to G1.
Speaking of shorts, a cathode to filament one would be worse as you can't clear those. However, with the use of a Brightner/Transformer they can be isolated.
You should be able to clear yours.

Hmmm, my Sencore book says G1 to G2, it turns the filament off and removes it from the circuit to protect it.
It also says bang away, if there are sparks there is hope. No sparks indicate a mechanical short.

Cathode to G1.
Speaking of shorts, a cathode to filament one would be worse as you can't clear those. However, with the use of a Brightner/Transformer they can be isolated.
You should be able to clear yours.

I had a 1959 Motorola 21" with an intermittent heater-cathode short that you could clear temporarily by tapping the neck. The pix would wash out, go dim and show retrace lines. Putting on a Brightner/Transformer did cure that problem. When it shorted after that, the picture then only got slightly smeary. Maybe the Brightner/Transformer winding coupling capacitance was attenuating the higher frequency video information. Rewiring the video circuit to feed positive-going video to the grid could probably remedy that. The cathode would be at a DC-only potential instead of G1. I just gave up and put the set with the other "almost-perfects":sigh:

Hmmm, my Sencore book says G1 to G2, it turns the filament off and removes it from the circuit to protect it.
It also says bang away, if there are sparks there is hope. No sparks indicate a mechanical short.

Wow...I know you mentioned about laying the set on it's face, but something must have lodged itself good to cause a short like that. Yes, sparks are good but I'd also consider putting the set upside down, sideways etc. in your attempts!

I have a fairly good book on this. Ill have to read up on it. My question is what is g1 shorted to? G2 or the Cathode? I would hate to blow that little think cathode wire open. From what you told me about the set I bet it was a factory defect and a customer return.
Maybe you could ask Timmy if he has any tips on clearing the shorts...?

now really why would anyone ask me how to remove g1 shorts or is it you forgot how to and your hopeing ill post how to remove them and you feel funny that someone here might find out that you may have forgotten, how to remove g1 shorts, lol,lol. well ok ill do it for you ctc17, here goes, on a bk 440 plug unit into outlet turn on let warm for a moment then check heater voltage first and set it . if it b@w then you leave the rgb switch on red and proceed with setting up for emissions test then turn switch from emissions to clear shorts but dont go to far as you may wind up with the switch landing on rejev low, so be careful now. and for best results turn the selector switch from emissions to clear shorts quickly and press the red button and watch the fireworks but the key is to switch to shorts and press the button befor the filiment light disappears, as the hot element expands things and brings them closer, ah the shorts, because if you wait like it tells you to its not as effective. oh and if its a color tube you would have to clear shorts on each gun, ah that would be red, green, blue, boy i wish i was as smart as you but then again why did i have to explain how to do this rather simple vintage task.:drool: good day

oh and yes i agree isolating the short would be a great idea, what do you think ctc17? oh and if its a cathode to filiment short..................................

Ohh Timmmmmmy, Relax! Cant you handle a shout out? a name drop?

lololololol...................................

I agree with Marty you should try turning the tube an all directions and try zapping it. But I think an hour or so with a good bright light, and carefully inspect the neck of the tube to see if there is anything visible as far as a shorting item goes..... Use an ohm meter too, check it to see if its short at 0v. operating voltage, or does it short only on full operating voltages. And at last resorts don't forget to remove the socket if the short is there at 0v. It could be a mechanical short outside the glass envelope.
I don't think I would do the 3,0000uf cap at 400V, you could weld with that much current. I would offer this: Tap the end of the tube, tap it harder, possibly vibrate it with a cell phone motor on the tube neck. And turn the tube, put the bad gun top, bottom. But I would still keep the gun horizontal, not lay the tube face up or down.
But that is just me. I got a lot of tubes going again with heating the tube, and wacking it good with a screw driver. Just don't break it, I bet you will run the possibility of making progress fixing this as long as you take your time and think it out.

roger all the ideas, currently the set is back with the owner, I am waiting to see when he can bring it back. I wonder if moving it may have caused something to break loose?

I was fighting with a stubborn G1 short over the weekend. The basic 'clear G1 short' function on my CR70 just wasn't clearing it out.
So, I re-read the full manual and discovered there's an 'Extended G1 Short Removal Procedure' ! It's not even mention in the abbreviated manual inside the lid.

You can download the relevant pages here: http://www.bobandersen.com/images/scanned%20manuals/Sencore/SENCORE%20CR70%20Remove%20G1%20Short.pdf

The basic idea is you disconnect G2 to reduce the chance of damage, heat up the short using 'Manual Restore 2' and blast it with 'Clear G1 Short' before it cools down.

Good luck - it worked for me :)

I am going to print that out and keep in in the case.

Bob, should we be expecting a video on clearing the g1 short?

Bob, should we be expecting a video on clearing the g1 short?

Maybe. I'll see what I can put together.

Unless you have a direct heater to cathode short of which a isolation transformer will cure, other type shorts are usually a minute speck of debris lodged in the gun assembly somewhere. Many times you can clear a short of this type by using a tesla coil "sparker" by running it around the pins on the base. In rebuilding tubes you would normally do this if a tube was showing signs of internal arcing due to impurities. (Not a continuous arcing, just a flash every now and then) Try sparking the pins and see if this will work. These types of tesla coil hand sparkers are normally used in vacuum work to look for leaks. This same type of device is also found in 1930-40's medical cases that had ultra violet tubes of various sizes to rub on your skin. If you have access to one, just stick a wire in there and run it around the pins.