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Rejeuvenating 813's




 
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WU2D
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« on: December 11, 2009, 09:47:26 PM »

I have one lighting up the bench tonight - nice lamp.

The idea is to grab a Variac, an 18-24 VDC, 5-10 Amp Transformer, a meter and a soft 813 and bring back its emission.

I assume that you have a tube that is not gassy (no smoky getter) and has some emission. My tube is not a dud. It is a good quality USN marked 813 by RCA. In my case I had an 813 doing 100 Watts out in my ART13 with 1500V on the plate. Grid current was about half into the acceptable drive range (center paint on the meter). This experiment will see if we can bring the power up a bit.

First the tube is set right side up and the clip leads are attached from the large pins to the transformer secondary. The meter (AC) is used to monitor the voltage at the filament pins.

Step1 Light the tube up at normal voltage  10 VAC

Step 2 Increase the voltage slowly to 15 VAC - yes 150% of 10VAC and leave it in this bright scary condition for 60 seconds.

Step 3 ASSUMING YOU DID NOT OPEN THE FILAMENT:  Reduce the voltage to 11VAC and leave it there for 2 Hours.

Step 4 Let the tube cool and install it back into the radio and test.

I will let you know how I made out on this fun little test.

Mike WU2D






The sources of such dangerous behavior are:

http://amfone.net/AMPX/67.html (AM PRESS EXCHANGE ISSUE NUMBER 67, DECEMBER 1988 / JANUARY 1989)

and

http://www.antiquewireless.org/otb/rejuve.htm
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WU2D
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CW is just a narrower version of AM


« Reply #1 on: December 12, 2009, 12:38:49 PM »

The results after doing two tubes show that something is up in the ART-13. My output power and efficiency is down. It is modulating nicely and the scope looks fine but I am stuck at around 100 Watts out with normal grid drive. I should be closer to 125W out on 75M. I will have to do a tip to tail check in the PA compartment. The clincher would be an eyeball from Al, W1VTP who has a couple of fresh 813's he has offered to bring over for a visit (they must go home).

Tube 1

813 RCA USN 1942 

I have been using this used war vet tube for 1 year.

Initial Conditions:
Grid 40% above min Normal range, 1400 VDC 150 mA 210W input Power - 90 W out

After Treatment

60% above min normal range 1400 VDC 160 mA 224W in 100W out

Only slight improvement.

Tube #2

RCA RadioTron from 1950's

Very beat up with a loose plate cap - bounced around 20 hamfesters- nasty. Grey ring showing around top of base and glass.

Initial conditions:

Grid below acceptable, 1400V, 95 mA, 133 W input, P out 35 Watts! A beauty.

After Treatment:

Grid now in middle of range, 1400V, 170 mA, output Power 110W.

Emission pretty much restored.


Thoughts?  Mike WU2D   







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KC4VWU
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« Reply #2 on: December 12, 2009, 12:39:54 PM »

I've messed around with heater type tubes and was quite surprised that emissions can be improved, but I'd say that 75% of the time, they wouldn't bounce back. For those types, the process is sketchy at best.

The information is very good as a starting basis, and it is well worth trying. Let me know how the 813 works out; I have a few soft ones that i'd like to add to my lengthy "to do" list.

Speaking of "to do" list; how are you doing on that monster you posted earlier? Please don't feel alone by any means; I'd almost trade with you!

Phil 
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WA1GFZ
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« Reply #3 on: December 12, 2009, 03:31:33 PM »

I bought an 813 from a friend for Bob RKW. Then I noticed it had an X on the based. I showed it to the guy who sold it to me and he offered to give my money back. I suggested we test it to make sure. I noticed the pins were nasty coated with a nonconductive crud. Bob cleaned it off and it worked ok. I have a weak 4CX3000A that would make a good test case.
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WU2D
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CW is just a narrower version of AM


« Reply #4 on: December 12, 2009, 03:54:27 PM »

Again this information was from the AM Press exchange cited...

By the way I ran both tubes key down for 15 minutes with 100W out and air on the tube just to be sure that I had in fact done something permanent.

Tubes with the oxide coated cathode used in almost all modern receiving tubes, and in transmitting tubes such as the 807, 6146, 8874, 4CX250, etc. are not candidates. This type of cathode runs at a dull red heat. Unfortunately, you cannot rejuvenate this type of cathode.

The type of cathode you can possibly rejuvenate is the thoriated tungsten type, used in tubes such as the 805, 810, 813, 833, and 4-65 through 4-1000 series tubes -- filamentary cathodes that operate with a bright yellow-white glow. The thoriated tungsten filament is made by dissolving a small amount of thorium into the tungsten filament material, which forms a layer of thorium on the surface about one molecule thick. It is this thorium which does the bulk of the electron emitting when heated.

Mike WU2D
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W1RKW
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« Reply #5 on: December 12, 2009, 04:59:28 PM »

I bought an 813 from a friend for Bob RKW. Then I noticed it had an X on the based. I showed it to the guy who sold it to me and he offered to give my money back. I suggested we test it to make sure. I noticed the pins were nasty coated with a nonconductive crud. Bob cleaned it off and it worked ok. I have a weak 4CX3000A that would make a good test case.

Yep, it's still in the rig and working!

Nice bit of info Mike. Thanks for sharing.
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Bob
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His fear was when I turned it on for the first time life on earth would come to a stand still.
w1vtp
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« Reply #6 on: December 13, 2009, 09:41:39 AM »

Mike

I have an 813 that has a a couple of grey pieces that are floating around the inside.  No other alarming stuff to be seen.  What are the chances this is an OK tube?

Al
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WU2D
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« Reply #7 on: December 13, 2009, 10:10:05 AM »

Al,

Put it in the dishwasher - that seems to be what everybody is doing...

Dunno - let me ask the magic valve.

After rubbing the magic valve in my hair and gently blowing mist on the side, this is the message that came up:

"Does it say RCA?"

Mike WU2D
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W2PFY
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« Reply #8 on: December 13, 2009, 12:51:56 PM »

Quote
gray pieces

That's what we all get when we get older Grin Grin Grin

Maybe air,usually white means air so gray may mean not quite so much air but if you lite it up, the whole inside may fill with a white smoke, indicating air has seeped into the envelope.
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KM1H
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« Reply #9 on: December 13, 2009, 01:44:17 PM »

Quote
Tubes with the oxide coated cathode used in almost all modern receiving tubes, and in transmitting tubes such as the 807, 6146, 8874, 4CX250, etc. are not candidates. This type of cathode runs at a dull red heat. Unfortunately, you cannot rejuvenate this type of cathode.

Sure you can and its been published many times in the rags; and I used to recover soft 6146's at a good percentage. I took a quick look and couldnt find the info. Its my birthday and the family is taking me out so I havent time to look more but you guys are resourceful. Roll Eyes

I believe the one I used was in a Non QST rag of the 50's or 60's. It took momentary zaps of HV to boil of the cathode contanimation layer, probably based on picture tube rejuevanators.

Carl
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w4bfs
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« Reply #10 on: December 13, 2009, 10:08:05 PM »

happy birthday Carl ... please continue looking as this could be interesting .... how did your 860 type tube search turn out ?
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KC4VWU
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« Reply #11 on: December 13, 2009, 11:13:37 PM »

Carl is right and I'd like to read the info he's referring to. What I found was in the AWA archives; but from what little playing I did with it, I found it's kind of like rolling the dice. However, is it worth trying? Definately. I'd say the success rate was probably around 50%.


Phil
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W2PFY
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« Reply #12 on: December 13, 2009, 11:24:14 PM »

I wonder if big glass tubes were always a throw away after the tubes life? Were some of the large ones like 1000T 1500T and 2000T ever rebuilt??
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WD5JKO
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WD5JKO


« Reply #13 on: December 14, 2009, 12:08:23 AM »

happy birthday Carl ... please continue looking as this could be interesting .... how did your 860 type tube search turn out ?

  Carl,

   I'm pretty sure I have one of those. Contact me privately if interested. I had it on a board for years and years as part of a tube collection. Now it sits in a box. The filament was good 30 years ago. Undecided
If I ever finish this business trip, I can dig it out and look it over.

http://tubedata.milbert.com/sheets/049/8/860.pdf

Jim
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w1vtp
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« Reply #14 on: December 14, 2009, 07:46:45 AM »

Al,

<...>
"Does it say RCA?"

Mike WU2D

Yes but what difference does that make.  I guess I should just put the fil volts to it and see if I get a smokey the bear version of the Christmas ball with the snow (just smoke instead)

Al
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The Slab Bacon
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« Reply #15 on: December 14, 2009, 10:01:10 AM »

Mike,
       I have done this in the past with older receiving tubes (filament type) like '01As, 71s, 26s, and 45s. But especially '01As. The method I was taught was even more brutal, sometimes doubling or higher the filament voltage to boil up some new thorium. I have had a 50% or better sucess rate. If you toast it, it was trash anyway, so nuthin from nuthin leaves nuthin. I have even had some '01As that had absolutely no measureable emission test good as new after the torture. It just messes with your head seeing the filament literally "light up like a lightbulb".

the principal of the "rejuvenation" is to get the filament hot enough (right to the melting point) to bring some of the "fresh" thorium up to the surface of the filament wire. It does work if done right. But just like grandpa's secret BBQ sauce, everyone has their own special recipe for doing it.

                                                         The Slab Bacon
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K1ZJH
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« Reply #16 on: December 14, 2009, 10:02:08 AM »

Carl is right and I'd like to read the info he's referring to. What I found was in the AWA archives; but from what little playing I did with it, I found it's kind of like rolling the dice. However, is it worth trying? Definately. I'd say the success rate was probably around 50%.


Phil

Here's a question for the group. They used to sell picture tube rejuvinators. Why
couldn't one of those be adapted to drive electrons to the surface on cathodes in
receiving and small TX tubes?

Pete
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W1RKW
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« Reply #17 on: December 14, 2009, 05:30:56 PM »

does it matter if the filament is powered by AC or DC?  I wonder what effect would occur if at DC the polarity was switched like using a low frequency square wave.
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Bob
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Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
KM1H
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« Reply #18 on: December 14, 2009, 06:46:21 PM »

I just started looking and this is what Ive found sofar on the Internet.

http://www.freepatentsonline.com/2413707.pdf

IF I remember the magazine article tied screen to plate, about 250V B+ between plate and cathode and a momentary touch of the grid pin with the 250V.

The problem with 6146's and other TX tubes is that many are fried from excessive grid and screen dissipation and no amount of cathode zapping will fix that.

I'll keep looking.

Yes, Im still looking for a 860 and also a 861. Jim I'll drop you a PM later.

Carl
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WU2D
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CW is just a narrower version of AM


« Reply #19 on: December 14, 2009, 08:20:50 PM »

Al,

Bring your tube over for THE TREATMENT.

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w1vtp
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« Reply #20 on: December 14, 2009, 09:04:53 PM »

Al,

Bring your tube over for THE TREATMENT.



Sounds like a plan!  I'm off Christmas week.  Or maybe we could do something this weekend

Thanks, Al
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KB0HFX
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« Reply #21 on: December 29, 2009, 08:17:22 AM »

Hello all,
Finally found the info I had for "flashing" tubes. The technique was originally to recover a good tube that had its ratings exceeded. IE: making your graphite plates glow. According to the info the surface layer of thorium should replenish by diffusion from inside the filament thru the course of normal operation untill the end of life. As in it wont fix a soft tube just make it quit all together most likely.

Only for directly heated thoridated filaments 
As per sterlings radio manual.
Remove all voltages from the tube except filament
Operate filament at normal voltage for 20 minutes
If not recovered proceed as follows
Operate filament at 300% voltage for 30-60 second
Season at 150% for 10 minutes
restore to operation if still low-discard.

Austin
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