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 Post subject: Re: Jefferson radio tube rejuvinator
PostPosted: Oct Wed 30, 2019 12:11 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8949
Location: Long Island NY
The thread you are posting to is 13 years old, and Ken Owens, who was a good friend, passed away a number of years ago. Curt Reed and Alan Douglas are gone too.

The device Ken was talking about was a filament transformer that would deliver about 7.5 to 8 volts to an 01 or 01A. It is essentially what was in the old Jefferson (and other brand) tube rejuvenators. About 5 to 6 volts would be used on a 99. The process works with the thoriated tungsten filaments of 01 tubes by driving more thorium to the surface of the filament and replenishing it; with the oxide coated filaments in the 01As and 99s, it works by burning off the outer layer of the oxide coating and exposing fresh material. These measures can usually only be done to a tube one time with any degree of success, after which they may do more harm than good if you boil off the last remaining thorium or oxide. If somebody rejuvenated the tubes in the past, doing it a second (third, etc.) time could make them worse or kill them altogether. For that reason it should never be done on weak tubes that still work, only on ones that are so weak they cannot be used any more. People had many theories on how long the high filament voltage should be applied, or how many cycles should be performed, but most recommended no more than doing it one time for four or five minutes.

In any case results are iffy and you should be happy for whatever improvement you get--if any. There is no way to know how long a rejuvenated tube will last before its emission falls off again.

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 Post subject: Re: Jefferson radio tube rejuvinator
PostPosted: Oct Wed 30, 2019 5:20 pm 
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Joined: Mar Sat 14, 2009 5:56 pm
Posts: 4442
Location: VA 22602
I sold one of the Jefferson units here on ARF a few years ago with it's original carton. It worked well enough but I didn't feel warm and fuzzy using a nineteen-twenties device with any regularity. I had no room to put it on display in my workshop at the time so I chose to sell it to someone that would use it or display it. I just use any of my tube testers to cook 01A's at 7.5 volts to boil a fresh layer of Thorium to the filament surface. When using a tube tester you do not use the test setup, you only apply voltage to the filament. Some tubes rejuvenate, some don't. I have put several back in service over the years and I keep the rejuvenated tubes for my personal use since their remaining (restored) life is questionable.

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 Post subject: Re: Jefferson radio tube rejuvinator
PostPosted: Oct Wed 30, 2019 6:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 14411
Location: S. Dartmouth MA 02748-1225 USA
I have a Jefferson unit and another brand, (forgot)...

I have not used them but they both are designed for 110 volts. I would be cautious using them at today's 125 volts. Could be a bit high for the flashing step.

Just a few words about the rejuvenation process.

It is not a concocted scheme to save tubes. FWIR RCA mentions the process and it is in Government documents.

Tungsten filament tubes, those one amp tubes like the '00 and the '01 cannot be rejuvenated.

Oxide coated tubes like the WD-11 cannot be rejuvenated.

Some have used a raised filament voltage on oxide tubes with success. Evey time I have tried this I have 'Killed" the tube of any remaining emission...

The 1/4 amp '00a and the '01a can and the early 71 (not the "A"), the 210, (later 210 are oxide). Along with several others including larger vintage transmitting tubes can be rejuvenated.

There is one very important step that is not re-reinforced in all rejuvenating instructions. That is, the need NOT to connect the GRID and the PLATE to ANYTHING.

During flashing there is large amount of electrons available and the forces at that temperature holding useful thorium to the surface are very weak. ANY potential will remove the thorium in massive amounts, even to test the tube. It is a mistake to monitor the emission of a tube in process of rejuvenation. Let the grid and plate be free of all connection to any circuit.

I routinely rejuvenate with a Triplett tube tester, using the filament setting switch as the filament voltage control.

I have an "interposer" adapter that connects only the filament of the tube and easily plugs in/out. I do monitor the filament voltage with what ever meter is handy. I also use other socket adapters for tubes such as the Shaw base and the UV-'99 base.

Four-pin tube filament connection only interposer.
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There are steps to the rejuvenating process outside of the full force "flashing" & aging. If each step fails, move on to the more aggressive. That saves unnecessary "abuse" to the tube.

1 - In a battery set, burning the tubes at full brilliance with "B and "C" batteries disconnected for an hour or so. This was a routine procedure for 20's era radio fans. That would apply 6 to 6.6 volts to the tube filaments, grids would be grounded more or less via the radios circuits. The process would "wake-up" lazy tubes. Remember, Many early tubes were very inconsistent in their manufacture so some gas may be present, some filaments installed longer than others, etc. The burning would help to normalize the emission to some degree

2 - Using the known published charts for rejuvenation the next step for sleeping tubes is to apply the voltage for aging for the time advised NO connections to grid or plate. Failing this step.

3 - Full flashing, aging. Once again, no connections to grid or plate. If the tube fails yet the filament is intact. then all thorium is used up.

I'll add, 20's radio fans, frankly, pushed their sets with high volumes and earlier sets did not make use of grid bias. In a weeks time the thorium would get exhausted from the surface of the filaments particularly the audio tubes. Such tubes were referred to as "paralyzed". A term meant to indicate that the tubes could be revived.. Such service it was expected that tubes be replaced at regular intervals. Bumping up the plate voltage without the required "C" voltage or simply overloading the plate current could cause such an action.

If your a truly conservative collector/user, the process of rejuvenation may reveal gassy tubes from the normally non-gassy tubes. These discovered gassy tubes can be used in the grid-leak detector like a gas detector, however, results may not be what is expected from a built for purpose gas detector tube.

There is some usefulness to the thorium exhausted tube especially in a single tube receiver. That is using an "A" source that is more the 6 volts (for '01a) and using the tube like a 1 amp tube. There is risk the filament rheostat could get overheated :roll: Works until the filament parts...

Rejuvenating the gas detector '00a is a very iffy process. These tubes will not test correctly in some instances as the plate voltage must be very low to confirm proper operation. It has been said if the tube goes directly into ionization during a test it will be ruined, the filament getting bombarded with ions. I have not followed that through as I do not wish to destroy a tube to prove the failure mode...

To the poster henrypal who brought this topic back from the past.

Create the circuit if you want or need be it some sort of automation to the rejuvenation process. I have almost always done it manually using simple plug-in adapters to accommodate the tubes in the tube tester.

See Nostalgia Air article for tube charts, times/voltages.

http://www.nostalgiaair.org/References/ ... lash08.htm

GL

Chas

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