Posts: 4,377
Threads: 411
Joined: Jun 2011
City: Boston
State, Province, Country: Massachusetts
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
Tubetalk1
Posts: 15,691
Threads: 551
Joined: Oct 2011
City: Jackson, NJ
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.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 7,283
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
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
Posts: 4,377
Threads: 411
Joined: Jun 2011
City: Boston
State, Province, Country: Massachusetts
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
Tubetalk1
Posts: 7,283
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
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
Posts: 4,682
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
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
Posts: 1,183
Threads: 23
Joined: Jan 2014
City: Wellborn Florida
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
Posts: 2,128
Threads: 18
Joined: Oct 2008
City: Merrick, Long Island, NY
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.
Users browsing this thread:
|
Recent Posts
|
Jackson 715 not working
|
Mrfixr55, its working now. I cleaned the switches and sockets with spray cleaner. Thanks for helping on this one.daveone23 — 06:26 PM |
Jackson 715 not working
|
Now that you posted the schematic, I don't know why that Sprague electrolytic cap is across the meter, as it is not indi...MrFixr55 — 05:51 PM |
HiFi (Chifi) tube amp build - but my own design.
|
What may be lacking in the PP Tube amps may be the 2nd harmonics, which some, especially RCA back in the day called &quo...MrFixr55 — 05:32 PM |
Jackson 715 not working
|
Usually in an emission tester, the tube under test is measured as if it were a diode. So, some testers connect all the g...RodB — 04:17 PM |
Restoring Philco 37-604C
|
Yep. F5 is green, D5 is Red.
Red is Bad.
Green is Clean.morzh — 01:30 PM |
Jackson 715 not working
|
I did start to do that but I stalled out because I could not figure out how the grid and plate get voltage. In this diag...daveone23 — 11:52 AM |
Restoring Philco 37-604C
|
(Insert Homer Simpson "DOPF" Here.)
When all fails, look at the can. Took the Ron Ramirez advice, red Caig D...MrFixr55 — 09:23 AM |
Philco 91 Speaker Replacement
|
From your text I am not sure if you intend to use the existing speaker with a resistor instead of the field coil.
It wo...morzh — 08:44 AM |
Philco 91 Speaker Replacement
|
My field coil is bad. I am still hoping to find an original, but if I can't I will go with a fitting Philco speaker, 125...dconant — 08:34 AM |
Philco 91 Speaker Replacement
|
As Rod said, it is OK to use a fitting speaker, and then look for an original one.
If you buy a Hammond 125 output tr...morzh — 08:15 AM |
Who's Online
|
There are currently no members online. |
|
|