top of tube blowout

[dirtyjob]

well title says it all, just got delivered a ft101e, used it with tube heater off :finals not engaged" for the 1st night since i didnt have a mic wired to it anyways, no issues cause the tube finals were not engaged, 2nd day i wired up a silver eagle and followed the manuals tuning procedure to the letter, talked to a friend for 30 min, he reported it sounded excellent, we were on am and i was seeing 10 watt dead key modulating to 50-60 watts.

Now this is my 1st ft101 series radio so i have no idea what they should be doing on am, is the output i stated normal ?? I usually inspect the tubes 1st thing when i get a radio delivered, this time i did pop the top and did inspect the driver tube but slacked when it came to the 2 finals "they as you prolly know are incased in a protective cage and i didnt open that up as I should have"


Anyways, as stated I was talking local for 30 min or so, seeing 10 watt dk with 50/60 watt modulated and my pal said he would brb, I said ok and was left alone, while he was gone I wanted to key up to again see the output on my external meter, well expecting to see that 10 watt dk I instead had nothing, no output, zilch, well I was like wtf.. so i looked inside and saw now that the only tube lit up and functioning was the single driver tube.. the 2 finals were not lit, so theres why i had no output, but why.. so I popped the top of the high voltage cage after I shut it down and here is what I saw:

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A Huge chunk of one final was totally gone and now resides at the bottom of the socket in one big piece.

Now Im like "that sucks" but what do ya think caused this?? Improper tuning ?? or do ya think it was damaged in shipping ??

Also, i need to take it out of the socket but dont want to get belted, How do I discharge this, someone in a fb group said to take a screwdriver and touch the top of the tube to the chasis.. is this correct ?? I dont want to do more damge to the rig or myself.

and what about replacing the set, how do i neutralize ?? any help on all this is more than appreciated.

[MDYoungblood]

To discharge a cap safely look up a "Salisbury Capacitor Discharge Stick" , it will save your life.

You can make one fairly simple with a metal pointed plastic probe, a 5 to 10w resistor, (a light bulb will work too), wire and an alligator clip. Wire it all together in that order, attach the clip to the chassis and touch the caps on an exposed leg, hold it for a couple minutes (or the bulb dims out), do all of them.

3's

Greg

['Doc]

The 'quick-n-dirty' way of doing it is by shorting a screwdriver from the chassis to the tube plate cap. That's gonna 'eat' a speck out of the screwdriver blade, probably, but it's about the most common way of dong it. It's chasis contact FIRST, then the plate cap! Otherwise be prepared for a nasty surprise.
So why did your tube give up it's ghost? Wooo, lots of possible reasons, no idea which one is the right one. If the tuning was done correctly then I would have to say that the tube was just ready to die. It happens.
- 'Doc

[Skipper 169]

I "grew up" in my Dad's shack, right after WW2 with all that surplus stuff, tube stuff, and never saw this happen. They call these things vacuum tubes for a reason though, and it had to have broken like that, maybe even when you were opening it up. If it had been cracked earlier, in shipment, it never would have lit up if it had lost vacuum, it would have burned out the filaments. And if it had blown the top off during operation, you should have smelled it. Probably heard it. Did you hear the glass rattling around in there as you were opening it?

[dirtyjob]

thanks for the responses thus far, I was able to get the tube out, prolly not the smartest way but i used a automotive insulated test light, put the ground clip to the rigs chassis ground and touched the top of the connected tube. No sparks or any indication voltage was present "Hope nothing else is wrong"

as far as why it blew/broke, ya i guess its a mystery, no pop/boom/smell at all, one minute i was talking the next no output/broken tube, btw i removed the broken glass, it was all in 1 piece, no small bits, just one big piece of the puzzle to grab which i find strange too.

What about when i replace the tube, should I replace all 3 "driver and 2 finals or just the 1 final or a set of finals ?

Also the previous owner had writen on the inside of the case top "Use American Tubes" is that due to a mod he may have performed or is he just on a buy American kick ?

Then there is also neutralization, is this another possibility to get me killed ? Should I skip that and hope for the best or should I do like the manual suggests?

[721HACKSAW]

It was probably just asking too much from a rig several decades old, AM operation is the hardest on all of those old components, especially those 6JS6Cs.... That was a lot of output wattage on AM for that rig in my opinion. The tuneup procedure is very critical on this rig also.
Originally the radio was supplied with a very high quality Toshiba tube, which hasn't been made in a long time, other manufacturers have produced this tube also, but with small differences that must be accounted for in the radios circuitry when replacing the originals, apparently your radio has had these changes done, hence the written note. Those later tubes are the only ones you're going to be able to find anyway.
Different tubes can be retrofitted to the rig but the changes are extensive.
They made a lot of those radios, they were very popular, sites like this link have a ton of info... Such as "neutralizing" newly replaced tubes.
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I sold the one I'd had for several years because of the lack of tubes available..
Good luck and enjoy.

[dirtyjob]

thanks hacksaw, i have been to that site, there registration is bugged but i managed to email the admin and they manually registered me there, good info on the 101 series there for sure.

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Sunday, 06 April 2014, 12:11 PM

ok, installed and neutralized a new pair of finals in my 101e, now perhaps someone can offer me their tune up procedure on this rig, it's new to me and I dont feel like blowing up these finals.

[Skipper 169]

Mark, did you get this tuned up OK? I have watched this several times and have it on good authority that this guy is one of the best.

Yaesu FT-101B; Tune Up Procedure.

The good authority is the guy I bought mine from, on the truck as I type and be here Friday.

I am interested in how you did the tube neutralizing.

[dirtyjob]

i love that guy and that is exactly who I messaged on this subject, I did what is called a cold neutralization and the rig has been working great ever since with full output without issues.

[Skipper 169]

Where did you find the steps for the cold neutralization? In the service manual?

[dirtyjob]

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