[gennet2]

I have an new problem. Recapped 42-380 Philco. Including electrolytic caps. Had it on bench and have been playing it for several days on and off, worked good no problems. Decided to put it back into the cabinet and hooked up antenna leads. Turned on, it played for about 2 min. and it quite when I looked in back 6X5 tube was glowing blue unplugged unit imeadiatley. pulled tube and checked and of course it reads bad now. Only other thing I could find was transformer was quite hot. A quick plug in confrimed other tubes still lite as does the dial lights. Ordered another tube and hope that was the problem. Or should I be looking for anohter reason for this to have happpened.

Bob

[codefox1]

There has been a lot written about the notorious 6X5. The 6X5GT is less prone to failure. Personally, I'd use a couple of silicon diodes, a dropping resistor, and if you want, you can leave the 6X5 there, just disconnect everything except the filament.

[Arran]

The 6X5GT is fine as far as I know, I have several sets that use a 6X5GT and there is no evidence of any problems, some still have the original tube, the ones with the X pattern plates seem the most robust. I guess it may depend on the internal structure and how much current load is put onto the tube. Before you power the set up again I would double check your work and also see if maybe there is a short somewhere down the line after the rectifier, when they glow blue or spark that's often the cause. It could be a failed newer component, it does happen, or it could be a blob of solder they got into the wrong place. I'm not suggesting that the tube didn't fail but it isn't the only thing that could fail.
Regards
Arran

[gennet2]

Thank you both for your responses. I will look things over to see if I see anything out of place and try this first. When I get new tube I will see what happens. Hopefullly it was just the tube gone bad.
Bob

[gennet2]

Put new tube in and played for several minutes than boom!! 6X5 overheated and turned blue again. I checked wire all seemed good. also looked for solder etc that may be shorting out 6X5. could it have anything to do with the tow electrolytic caps I replaced. both are !0s one rated for 450 volts the other 500. Can caps be my possible problem?

[Arran]

Put new tube in and played for several minutes than boom!! 6X5 overheated and turned blue again. I checked wire all seemed good. also looked for solder etc that may be shorting out 6X5. could it have anything to do with the tow electrolytic caps I replaced. both are !0s one rated for 450 volts the other 500. Can caps be my possible problem?

It has to be, it's highly unlikely that you would end up with two failed 6X5s in a row if the second one was new in the box. If one of the electrolytic caps was hooked up backwards by accident it could cause a problem. Even if you didn't it still isn't unknown for one to fail right out of the box. I would suggest using your ohm meter on the cathode side of the 6X5 to see how much resistance there is between it and ground/B-.
Regards
Arran

[gennet2]

Thanks Arran for the reply. I have an ohmeter but can you explain how I can tell which is cathode side of socket. I assume If I ground to chassis I should not get a reading at all??
If I get a reading it would be a dead short to ground?
Also would it be wise to replace both electrolytics to tube 6X5. (exisitng are connected correctly with ground). And can I assume a regular cap even if bad would not have the ability to blow tube 6X5 on there own. Since it played well for several days before, I figuire everthing was hooked up correctly or it wouldn't played for several days. I did check wires from socket and replaced any that had cracked wire that may have been shorting out.
Bob

[Raleigh]

The cathode of the 6X5 is pin 8. You can get a pin-out diagram here: http://www.nostalgiaair.org/ Click on "Tubes" and then type 6X5 in the search box that says "Type" over it.

Looking at the bottom of the socket with the chassis upside down, you count the pins clockwise from the slot in the socket. Pins 4 and 6 are not shown in the diagram because nothing connects to them, but they are there in the socket, so count 'em anyway. Pin 8 is the pin to the right of the slot if the slot is pointing right at you.

If all caps are good, and if there are no shorted wires, you should get infinite resistance between the cathode and ground. (Somebody correct me if I'm wrong about this.) Your reading might be lower for a few seconds while the electrolytics charge up, but after that your reading should be infinity or "OL" on a digital ohmmeter.

If you see any path to ground (resistance other than infinity), you could test all three electrolytics by disconnecting the positive side and measuring resistance across the cap. It should be infinite. This is not a perfect measurement for leakage, since in operation there is high voltage across them (depending on which cap) but it is better than nothing.

If your multimeter will measure capacitance, try that. Are the electrolytics rated for 450 volts?

There are a few possible sources other than the electrolytics for B+ shorting. I'm pretty sure that each of the IF transformers has rubber wire inside which could short. I always take the IF cans out to replace all the wires and test any components inside. If you read a short with your meter, you might try wiggling the wires going into the cans to see if it makes a difference. If it does, replace or re-insulate the wires.

It is unlikely, but the plate or screen grid in another tube could be shorted. It might be a good idea to test all of them. I've had tubes short spontaneously, and I once caused one to short by putting it in the wrong socket. It is not unheard of that a tube will short when it is handled, even gently.

Sometimes shorts show up when a chassis is moved, even when it operated correctly beforehand. I remember a restorer on another forum whose radio (not a Philco) would operate fine on the bench but shorted every time he put it in the chassis. Because of the rubber wire, your chassis is probably especially vulnerable to intermittent shorts.

[Arran]

Actually the rotten insulation theory make a lot of sense, since you were trying to recap the radio it's very possible that some of the old wiring was disturbed, the insulation flaked off, and it is now shorting to the chassis. Since the IF cans from this era have the same crappy rubber wire as the rest of the radio, and one side of the IF cans is connected to B+ anyhow, this could be another place to look. The wiring to the IF cans should be replaced anyhow, the last early 40s Philco I worked on needed it too. Just make sure that if you do replace the wires do it one at a time and copy the route and length of the original wire, it's a bit tricky to do but not as bad as changing the micas in an IF fro the 1950s.
Regards
Arran

[gennet2]

THank You so much Arron at least I have something solid to go on now and will check the wires very carefully. I have a hunch there is a bad wire somewhere. I will keep you posted on my progress as this has become a chalenge to me now!! I am not going to let this radio beat me. I did recieve a book I ordered online, Antique radio repair by A Corbin .
MAYBE I'll learn something from it.
Regards Bob

[gennet2]

Hi Arran, well I think problem is solved. Radio now is working fine agian. had it on for about 10 min. and no 6X5 tube blowing out. I checked some of the wires and there were two questionable as far as rubber insulation goes, both off tube 6X5, replaced them I checked pin #8 for continuity to ground and didn't read a thing. Only other thing I thought of was radio worked fine till I put in the dial bulbs. Looked the sockets over for dial light and the hot lead was bare where it comes out of the socket. that may have shorted to ground. (Don't know if that would cause problem or not.)
Or maybe new tube went bad. But seems unlikely original tube burned out as well as new one.
Anyway thanks for you help.
Bob

[Ron Ramirez]

This is why I tell everyone that all of the rubber insulation on the wires of the 1939-1942 Philco models must be replaced! If it hasn't dried out and started crumbling yet, it will.

A dial lamp lead shorting to ground could have damaged the power transformer. I do not know why that would cause the 6X5 to blow, however. How are the leads connecting to the 6X5 socket?

[Ron Ramirez]

To emphasize my point:

[Image: http://www.philcoradio.com/tech/images/rubber3.jpg]

Would you trust these wires?

I have revised my page on rubber-covered wiring in my site's Tech Section, adding several photos.
http://www.philcoradio.com/tech/wiring.htm

[Arran]

Hi Arran, well I think problem is solved. Radio now is working fine agian. had it on for about 10 min. and no 6X5 tube blowing out. I checked some of the wires and there were two questionable as far as rubber insulation goes, both off tube 6X5, replaced them I checked pin #8 for continuity to ground and didn't read a thing. Only other thing I thought of was radio worked fine till I put in the dial bulbs. Looked the sockets over for dial light and the hot lead was bare where it comes out of the socket. that may have shorted to ground. (Don't know if that would cause problem or not.)
Or maybe new tube went bad. But seems unlikely original tube burned out as well as new one.
Anyway thanks for you help.
Bob

Well thank John Honeycutt as well, he actually pointed it out before I did, the only thing I had to add was that during the recapping you may have disturbed some wires causing the insulation to flake and the wire inside to short to ground. I would still do as Ron suggests and replace the rest of the rock hard wire, especially if it's coming out of the power transformer, if it's cloth covered it can stay as long as it isn't moved to much, even cloth wire can be a problem if it gets hard and stiff.
Regards
Arran