[Paul Philco322]

I have no tube tester, poor widdle wold me, boo hoo. I usually use the old tube hunting strategy. I do have a question for those who have been at this stuff for a while. When a tube tests OK and then is playing in a set does it tend to degrade slowly over time or go pop?  I have had sets play fine and then sound weak and erratic fairly suddenly. Often a rectifier or audio output is the reason. Do these tubes tend to just blow because of higher voltages? Even after being fine today then poof tomorrow. I am imagining the other tube types may just get weak and then fail.

By far most tubes I change out are rectifiers or outputs. Another reason to go to the swap meet, tubes reasonably priced. 

Your thoughts appreciated.

Paul 

[morzh]

Depends on a tube, depends on a cause of failure.
A rectifier can go weak, or can go short, or can have filament open, or.....any device can have more than one failure mode. Some more popular than others.

[Radioroslyn]

Are we taking transformerless sets? Series strung jobs? I find that the rectifier and the audio output do have a higher failure rate. When the heaters don't light those are the first I check. Sometimes there is a paper cap between the plate and the heater on the rectifier that will blow out the tap for the dial lamp if it is bad.
Terry

[Paul Philco322]

Yes sir, AC/DC. I have a lot aof the little guys and find I go through rectifiers and outputs to the point where I do stock them when I get a good price as I did yesterday from a pal at the NEARC meet. From what I have been told some folks moons ago viewed radio as entertainment when the evening slowed and then turned on their set. Then there were people who listened all day long, background to life was radio, news, soap operas, cooking shows, sports, and all the OTR shows we listen to now. So some folks burned through tubes before other problems came up in the set. So maybe retubing was needed sometimes.....I do listen to sets and leave many to play for a while. It seems the 35Z5s and 50L6's go first and when I hear a reception issue, sound issue in a recapped set I look there first. But it seems at times they are good today and fry tomorrow, like a light bulb almost....

Paul

[Radioroslyn]

Well two things come to mind. Use a bucking transformer to lower the line voltage a bit like 12v or so. And be sure to use the proper dial lamp #47. It's a 150ma bulb that match the current of the heater string. A #44 will work but it's a 250ma bulb. May tend to imbalance the heater string at the rectifier tube.
Time for Jack Benny for WNAR via the web.

Terry

[Arran]

 In a restored set I have very seldom had any problems with tubes, didn't seem to matter whether it was a series string AC/DC set or a transformer type. In an AC/DC set if a tube blows something, like the heater or a cathode, there is usually an external cause like a heavy current load. I've bought sets that had tubes with an open heater but I've never had one fail in service once I overhauled the set. In one case I had the 35W4 die in a Canadian Pye radio, but I bought that set as working, the previous owner recapped it other then the audio coupling cap between the 50C5 and the 12AV6, but since I never checked the tubes it may have been on it's last legs when I bought it. In the other case of a tube going bad it was also a 35W4, but in this case it was the cathode connection that popped, the reason being is that the 50C5 was loose in it's socket and kept cutting in and out of circuit whenever the radio got bumped, it ran fine as a daily driver for ten years before that though.
 As for AC tubes, I've never had a rectifier fail whilst in service, in fact many of the sets I get still have the original rectifier tube in place, sometimes worn out but often they are fine. In my latest restoration job, an Electrohome, it uses a 6X5GT, the strange part is that one diode tests fine but the other tests weak, and it is clearly a replacement since the original would have been either a Westinghouse or a Marconi brand tube not a Rogers. The set still had it's original filter caps in it, so that may explain why the 6X5GT was replaced with the Rogers one and why it's weak on one side. On the other hand the 6K6GT that sits next to it appears to be an original, and tests quite strong, the 6SQ7 that drives it seems to be borderline.
 From what I can tell this was a set with a high number of hours on it, or at least medium high, every resistor is either drifted or open, the 6SA7 is a Japanese GT style replacement, and someone stuffed a 6SJ7 where a 6SK7 should be. It could be that the original 6SA7 may have died due to a lightening strike, as the B.C band antenna coil was burned up, but 6SA7 tubes tend to be driven hard anyhow since they act as an oscilator-mixer and first detector.
Regards
Arran

[David]

Looking at AC/DC set bad E caps are hard on the rect tube and the output tube. I have several set from around 1946-1960 and the only tubes that have been replaced are one or both of the above. Using a bucking transformer will help things out. I try to run my AC/DC sets 105-110 volts my line voltage runs 119-125 volts. David 

[codefox1]

Agree that many rectifier failures are due to faulty filter caps or shorts, and output tubes do age less gracefully than small signal tubes. And weak mixer/oscillator tubes may work fine in some sets, and not at all in others. A decent tube tester will help you identify complete duds and help somewhat in selecting matching pairs for example. Nothing beats having a stash of "known good" examples for first level differential diagnosis. Taming higher line voltage is always a good idea.