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37-116 odd noise/distortion - Printable Version

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37-116 odd noise/distortion - poulsbobill - 07-12-2022

Now, On start up i get a "blurp" sound (say it out loud---thats it)  after about 5 seconds and then the radio warms up and plays after about 15-20 seconds. I am also starting to get some distortion at the higher sound frequency's. (singing)  This has been hit and miss and less the longer the radio is on.

All this is new in the last 2 weeks.  The radio was recapped/resistored about 3 years ago by someone known to me to be reputable.  I play it about an hour every day.  I can hear something is going on, changing in the sound.  Yes this is AM radio and my reception varies greatly day to day but this is beyond that.

Since i believe the caps are ok and it does play well other that this occasional  higher frequency distortion/blurp, i am thinking a tube going bad?  

I dont have a tube tester.  All heaters are on, but i do have a few metal tubes.  They are warm,  not hot.
Start on the  Rf and Audio section?

http://www.nostalgiaair.org/Resources/199/M0013199.htm

Thanks

Bill

RE: 37-116 odd noise/distortion - RodB - 07-13-2022

Hi Bill, you are correct in focusing on a bad tube. I would change the 6J5 second detector tube first. But don't rule out a phlaky tube pin connection.

RE: 37-116 odd noise/distortion - poulsbobill - 07-13-2022

I took the 6J5 out ( its a metal one), cleaned the pins and cleaned the socket with contact cleaner and a airbrush brush i got at harbor freight. Put the tube in/out 3 times wiggling it each time. Fired up the radio and no "blurp" and no distortion. I will try again tomorrow as the "blurp" was only on cold tubes, but....

Thank you! Good call!

Bill

RE: 37-116 odd noise/distortion - poulsbobill - 07-22-2022

It's been a few days and the "blurp" has gone away, but while i was spending time in the back of the set i noticed this.
This is one of the 6b4g power tubes, they were purchased as NOS set about 2 months ago. You are looking at the right tube and the left one is in the frame.  I know it is dark but i wanted to capture this blue/purple glow.  It is about this bright with normal ambient light.

What is happening?  I switched the tubes and the glow follows the tube and not the circuit.  I have 2 heater circuits one with about 6.1 volts and one with about 6.6. You can see at the end of the vid that a small area stays blue once the tube warms up, but  it is not evident in the other tube.

I use a fake name for youtube.

Thanks

Bill

 [Video: https://youtu.be/llSyscjRO4A]

RE: 37-116 odd noise/distortion - klondike98 - 07-23-2022

My thought would be that the tube has become gassy, air leaked into the tube.

See:
https://philcoradio.com/phorum/showthread.php?tid=11962&pid=87101#pid87101 and
https://www.russoldradios.com/blog/previous/10 and
https://philcoradio.com/phorum/showthread.php?tid=16648&highlight=gassy

RE: 37-116 odd noise/distortion - poulsbobill - 07-23-2022

What symptoms would i be looking for as/if it gets worse? The getter is not white but light grey.

Thanks

Bill

RE: 37-116 odd noise/distortion - morzh - 07-23-2022

Why wait? Change it.

Also, if you have a tester, a good one, they test for gas.

RE: 37-116 odd noise/distortion - poulsbobill - 07-24-2022

i dont have a tester but i do have an old spare. What are the downsides of leaving it in? Of course anything is possible, but most likely bad things that could happen? I guess just trying to understand the failure...sure sound would suffer , have to replace but until then... is this a likely transformer ending event kind of thing/or...? Again, just trying to understand what is going on here.

Thanks

Bill

RE: 37-116 odd noise/distortion - morzh - 07-24-2022

Well, it might be an engineer in me talking, but the downside of leaving a faulty part in a device is exactly it - there is a faulty part in the device, and Gosh only knows what it might do and in what way it will fail (it will) and what the consequences might be.

One thing is a weak tube: it is a natural thing, it works worse than a good tube but it is safe and simply is not performing as good as it should. A gassy tube has a timebomb in it.

RE: 37-116 odd noise/distortion - poulsbobill - 07-25-2022

That's my question...what's the timebomb? What does a gassy tube do to the set on failure? Just trying to understand here.

Thanks,

Bill

RE: 37-116 odd noise/distortion - morzh - 07-25-2022

Gassy tube could develop large leakage and simply short something, or overload. Gas basically creates the conductivity where there shouldn't be any. Thus changing bias in unpredictable way.

Here's one account.

https://rec.audio.tubes.narkive.com/hPonD07A/tube-failure-mode-gassy

RE: 37-116 odd noise/distortion - poulsbobill - 07-25-2022

Ok i get it. I pulled the tube and for now replaced with an older one. Talked to the seller and he will replace the gassy tube.

Thanks

Bil

RE: 37-116 odd noise/distortion - Paul Philco322 - 07-25-2022

For the cost of a tube even a not so usual tube
worth doing.

Good luck.

Paul

RE: 37-116 odd noise/distortion - mikethedruid - 07-25-2022

OK, so, now you know why those of us who get into restoring antique radios buy a decent period tube tester. You will want one which tests all the early sizes, 4, 5, 6, and 7 pin base, as well as octal and locktal base at a minimum. They can be found on eBay. They are not as cheap as they once were, but are still worth the money if you really get into this hobby. Once you get one, replace any paper and electrolytic condensers in it.

RE: 37-116 odd noise/distortion - morzh - 07-26-2022

600A Hickok to me has the best price/performance ratio.
Of course 539 is better, and then there are some better still, but 600A will do most, if not all, that you need for restoring radios.