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Was working, now trying to burn up! - Printable Version

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Was working, now trying to burn up! - BenWA - 09-12-2014

I bought a Philco 41-608 yesterday and it already has been restored with modern capacitors by a past owner, but I admit some of the wire in the chassis should have been replaced but wasn't. The speaker wire and such is original and also needs replacement.

The radio was working nicely but suddenly when I was testing a pair of wires running with each other trying to find the power for the record player with a multimeter, it began starting to smell burning and a couple tubes got bright. I quickly unplugged it.

I never saw any smoke nor did anything seem to burst. I pulled the chassis out and I don't see any burned wires or capacitors underneath. but something is burning for sure.

With the chassis out of the cabinet sitting on plastic and plugged in to an outlet on a switch so I don't have to touch the chassis or radio at all, the dial light bulbs blinks some at first during the 'warm up' period, then there is a sizzling sound from the big power transformer and it gets very hot. There seems to be no leakage from it (yet..).


The small transformer next to it looks trashed. Is it the record player motor one?

[Image: http://img.photobucket.com/albums/v222/illiop/Philco%2041-608P/trouble1_1.jpg]



A vac tube directly behind it looks like it went bad. Could that be why?

[Image: http://img.photobucket.com/albums/v222/illiop/Philco%2041-608P/trouble1_2.jpg]

RE: Was working, now trying to burn up! - Mondial - 09-12-2014

Remove the 7Y4 rectifier tube and power up the set again. Doing this will remove the high voltage load from the power transformer. See if the transformer still sizzles and gets hot. If it does without the rectifier tube installed then the transformer is fried.

You may have a shorted 41 output tube which could be loading the power supply, but try removing the rectifier first. If all is well with the rectifier removed then reinstall the 7Y4 and try removing the 41 tubes next.

RE: Was working, now trying to burn up! - BenWA - 09-12-2014

Thank you very much for the reply. I pulled the 7Y4 tube and switched on the power to it... no sizzle, no burning.

That's what the problem was. I guess that's the tube just suddenly decided to kick the bucket. I hope it didn't take out the other tubes with it. The 7Y4 tube has the mirror finish in the top of it and several others have it too. However, after about 2 minutes turned on without the 7Y4, the rest of the tubes are very dimly lit so they may not be totally dead.

RE: Was working, now trying to burn up! - Mondial - 09-12-2014

Removing the 7Y4 and no sizzle does not necessarily indicate that it is bad.

Pulling the 7Y4 removes plate voltage from all the tubes, so there still could be a shorted 41 output tube or a short elsewhere. Reinstall the 7Y4 and remove the 41's and see what happens.

Did any of the tubes show a blue glow or sparking inside?

RE: Was working, now trying to burn up! - Warren - 09-12-2014

Removing the tube and not having a problem from there doesnt necessarily mean its the tube, but somewhere in that part of the circuit. Should check the rest of the caps, resistors, etc in that part of circuit. Check the tube with a tube tester also. Then you will have an idea.

RE: Was working, now trying to burn up! - BenWA - 09-12-2014

Yes... the 7YA did blue some after i started smelling burning.

I had the chassis installed when i first started smelling burning. One or both 41s, i don't remember now... I think got bright. Then I unplugged it. (before moving it to the outlet on a switch).

Then I pulled out the chassis and saw the 7YA flickering blue some. I mentioned it in another thread, saying quote:

"one of the front vac tubes is flickering blue inside like lightning some"

Then I realized I needed to just create a separate topic on the proper board for help with this, rather than continue in my introductory thread on the "home Radios" board.

RE: Was working, now trying to burn up! - BenWA - 09-12-2014

I pulled both 41s and reinstalled he 7Y4... the dial bulbs half-dim flicker some but I don't hear sizzling and the transformer doesn't seem to get excessively hot.

EDIT: I take that back! It began to sizzle and get hot on the second try.

RE: Was working, now trying to burn up! - BenWA - 09-12-2014

Of all the good luck I could have, this company is LOCAL! http://www.worldtubecompany.com

Although, the address seems to be the guy's house.. a home office business. Not an actual store front. But that makes sense. There can't be much money in old vacuum tubes.

His website offers free tube testing. Normally you have to mail the tubes to him for test... but since he's a mile and a half away from me.... I could just drop by and have test the tubes while I wait. He also says on his site he sells tubes so perhaps he'll have a reasonable price on his tubes if they check out bad.I sent him an email... so I'll see if he replies in a few days. If not, I'll give him a call on Monday.

RE: Was working, now trying to burn up! - Phlogiston - 09-12-2014

Over the years I have restored many radios "recapped" by others. In about half of these, the reason the radio did not work was because of the work done - or not done. Do not trust an unknown "technician's" work. Any repairs should be verified prior to operating the device (radio). If you continue to run the transformer into an excessive load it will fail.

RE: Was working, now trying to burn up! - BenWA - 09-12-2014

Oh, don't get me wrong. It WAS working fine until today when I tried checking voltage on a pair of wires. That was probably just a weird coincidence, however. I had nothing crossed and I didn't tamper with anything except connecting an un-powered (no battery needed) analog multimeter to a pair of wires that may have been badly wired up by someone who had it before. That shouldn't have caused a mess of trouble since the multimeter didn't get fried, and it was on the setting for AC voltage metering.

And trust me, I'm not trying to burn it up. Icon_lol It hasn't even been plugged in since the second test with the 41's removed and the 7Y4 in, when I found it was overheating on that second check. I'm gonna try to get the suspect tubes (7Y4, both 41's) checked out and replaced if needed before it gets plugged in again.

Frankly, I think the 7Y4 rectifier tube just decided to bite the dust at the same time as I was checking those wires for voltage. After all, it may be a 73 year old tube! The 7Y4 one is Philco branded. One of the 41's is a Westinghouse and the other is Sylvania. The only other Philco tube still in it besides the 7Y4 is the 7C6.

Although, I know less than nothing about vacuum tubes right now. Icon_wtf

RE: Was working, now trying to burn up! - BenWA - 09-13-2014

I went on the local library's website and found two books and placed them on hold for pickup:

How to repair old-time radios / Clayton L. Hallmark (1979)
Old time radios! : restoration and repair / Joseph J. Carr (1991)

Those should be most helpful, if only for understanding how these old beasts work.

RE: Was working, now trying to burn up! - BenWA - 09-13-2014

I got an email reply from the guy saying basically "sure!" to bringing by the tubes for free testing. I have the chassis totally out of the cabinet now... maybe I'll just take the whole thing for him to see. Then I can get all the tubes tested by pulling one at a time. Perhaps he'll also be able to help diagnose the problem if the tubes somehow check out all good, since he's most likely an antique radio hobbyist also based on his website.

I figured out to unplug the speaker cable (it's in HORRIBLE shape with bare wire showing! I need to redo that ASAP!) and I ended up cutting 4 long, small wires but I marked them with black marker in such a way I know which was which. It 's old original wiring that needs replacing anyway due to insulation deterioration, like the speaker wires are.

I have done extensive repair and new wiring in my camper van so I'm comfortable with that aspect of this work. Icon_lol

RE: Was working, now trying to burn up! - BenWA - 09-13-2014

I may have crudely found my 7YA tube as bad.

I found the pin out of it online from several sources:
http://tdsl.duncanamps.com/show.php?des=7Y4
http://www.mif.pg.gda.pl/homepages/frank/sheets/121/7/7Y4.pdf
http://tdsl.duncanamps.com/link.php?target=F7255F82

As I understand it, 1+8 should have continuity, 3+6 should also, and 7 should be isolated(?). However, with my good multimeter with audible alarm continuity setting; 1+8 connect to 3+6 and to 7. All 5 pins are connected to each other inside the tube.

I found a topic over on AntiqueRadios.com where someone had the same problem ad came the same conclusion on the same tube:

Quote:I found a short between pin 7 and 1/8. I checked a 7y4 tube I had laying around it showed continuity between 1 and 8 but not 1/8 to 7. So the 7Z4 tube is shorted. It was a NOS tube from a local shop. My previous (original tube) became shorted also.

A comment from someone else states:

Quote:If you are able to measure continuity from pin 7 of a 7Y4 to pins 1 or 8, it is definitely time for a new tube.

I'm still gonna take my tubes to the guy for testing tomorrow.

The thread I am quoting from: http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=175997

Further reading I have done, I see that some people wire in a fuse to protect the transformer in case of a rectifier tube failure. This sounds like a very good idea to me. Had I been out of the apartment to go check the mail when the tube died instead of being right there with it checking for voltage, I might have come back to the apartment on fire from this!

I am definitely interested in wiring in a fuse folder to protect it from catching fire.

RE: Was working, now trying to burn up! - BenWA - 09-13-2014

Even if I find that that it was a bad tube, I need to go back and re-restore it. It was only half done, in my opinion. Lots of rotten insulation wires are left in the chassis. In a few months, I will get around to buying a small workbench a work light as well as an adjustable arm lamp. Trying to work with a flash light, even just to look into the chassis, stinks. The chassis on this radio is so cram packed that it's hard to make heads or tails out of things. It might be due to poor restoration or maybe it's just the nature of the beast.

RE: Was working, now trying to burn up! - sam - 09-13-2014

hey ben
I find the magnifying glasses with lights on side, head band type work great
and a heat gun on low to heat stiff wires work great to move them with out cracking them
before turning on again recheck every thing replace all bad and bear wires if you don't have variac use dim bulb set up
sam