Hi,
I got a new toy which is a tube curve tracer which allows as well to program individual regeneration routines per tube type (RoeTest - Röhrenprüfgerät Röhrenmessgerät).
It is a marvoulos system, which allows you to heat with any voltage you want, or anode voltage up to 600v, -ug til -100v etcetc.
So besides all the great stuff about testing and tracing etc, you can write routines where you give the tester a sequence like:
1. Heat only at normal voltage for 30sec
2. continue to overheat at 145% heater voltage for 2min
3. contine to apply 200V and vary grid voltage until 200mA emission and while the tube is getting red anodes, continue to decrease grid voltage to stay at 200mA
4. reduce heater voltage step by step until normal heater voltage is achieved
obviously you can choose connections as you like, so you could connect all grids to anodes for the procedure above.
Here are two spreadsheets with example procedures:
https://www.radiomuseum.org/forumdata/upload/Regenerieren_von_Roehren_1.xls
https://www.radiomuseum.org/forumdata/upload/Regenerieren_von_Roehren_2.xls
...so this is all I know...before now going and just destroying some tubes in trial and error, I want to ask those of you, who did the job before about your experience...?
My more specific questions:
- Overheat: How ? Heater-Voltage high or Anode-Voltage or both ?
- How long ? The speadsheets above indicate 15min per step, which means easily 90 min...? Or only 2 mn per step ?
- Connecting all grids to anode first and then all grids to cathode...? g1,g2 and g3 ? This will give a very low anode voltage...given that 200mA should not be exceeded...?
- which difference per tube type / chemistry ( barium vs. others )?
- "Your program" for popular tubes, say el34 ?
I guess it would be interesting to understand what the initialization process in the factory does and looks like...
I got a new toy which is a tube curve tracer which allows as well to program individual regeneration routines per tube type (RoeTest - Röhrenprüfgerät Röhrenmessgerät).
It is a marvoulos system, which allows you to heat with any voltage you want, or anode voltage up to 600v, -ug til -100v etcetc.
So besides all the great stuff about testing and tracing etc, you can write routines where you give the tester a sequence like:
1. Heat only at normal voltage for 30sec
2. continue to overheat at 145% heater voltage for 2min
3. contine to apply 200V and vary grid voltage until 200mA emission and while the tube is getting red anodes, continue to decrease grid voltage to stay at 200mA
4. reduce heater voltage step by step until normal heater voltage is achieved
obviously you can choose connections as you like, so you could connect all grids to anodes for the procedure above.
Here are two spreadsheets with example procedures:
https://www.radiomuseum.org/forumdata/upload/Regenerieren_von_Roehren_1.xls
https://www.radiomuseum.org/forumdata/upload/Regenerieren_von_Roehren_2.xls
...so this is all I know...before now going and just destroying some tubes in trial and error, I want to ask those of you, who did the job before about your experience...?
My more specific questions:
- Overheat: How ? Heater-Voltage high or Anode-Voltage or both ?
- How long ? The speadsheets above indicate 15min per step, which means easily 90 min...? Or only 2 mn per step ?
- Connecting all grids to anode first and then all grids to cathode...? g1,g2 and g3 ? This will give a very low anode voltage...given that 200mA should not be exceeded...?
- which difference per tube type / chemistry ( barium vs. others )?
- "Your program" for popular tubes, say el34 ?
I guess it would be interesting to understand what the initialization process in the factory does and looks like...
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When I worked with servicing of Tv sets, we used to regenerate old worn out picture tubes, by similar methods. The success rate varied, but a rather big percentage got a much better picture, and some kept on working for several years, such as a couple of my own sets. The regeneration, or revunenation as it is also called, works by burning away the surface of the cathode that has low emission, and exposing fresh material with higher emission.
Understood...and I would not touch a valvve which works fine. But sometimes you have those candidates like the Philps DD El34 from the 50s, which has only 54% emission left and you want to give it a second life...and some colectors even swear on their success rates when it comes to barium / thoriated tungsten types...
But my question was not to do this or not to do this. I will experiment with this in any case...but it would be nice to collect some knowledge upfront.
But my question was not to do this or not to do this. I will experiment with this in any case...but it would be nice to collect some knowledge upfront.
There is a patent on heater initial overpower that improves the statistics of better h-k resistance during manufacture, and for rejuvination - circa 1950s I think. I'll look it up later today.
I'd also be interested if you could determine if slightly gassy valves could be recovered by selective getter heating of some kind.
I'd also be interested if you could determine if slightly gassy valves could be recovered by selective getter heating of some kind.
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Typical consumer "receving tubes" die for two main reasons. Loss of emission, vacuum contamination (often called gas) or both. Shorts and alignment issues do happen as does an open heater, but these are less common.
Overheating the anode will not help any general purpose receiving tube. It will only make the gas problem worse and not help the loss of emission.
I borrowed the CRT zapper from the TV shop about once a year and shocked the picture tube back to life in my old 1957 vintage color TV (with a mid 60's vintage CRT in it). It worked by overheating the cathodes (about 8 or 9 volts on the 6.3 volt heaters), then discharging a cap between the cathode and all the other grids at the press of a button. As stated this ripped the worn out oxide layer off the top, exposing new material which had better emission. Occasionally it would create an cathode to G1 short which could often be cured with another push of the button. The CRT's heater voltage would then be returned to normal for several minutes and the emission readings taken again. The process could be repeated if there was no improvement.
Obviously this can't be done forever because the cathode will eventually be destroyed. I started with a free CRT pulled from a dead TV and kept it alive for 6 or 7 years, back in a time when color TV was rare and expensive.
The grid in a CRT is made of solid metal with a hole in it. It is physically stronger than the wire grids in a receiving tube, so the same process might be useful, but scaled down.
Some specialized tubes and many transmitting tubes can be "degassed" by overheating the anode, but they were designed this way. It has been reported that you can rejuvenate some receiving tubes by baking them in an oven, but I have not tried this.
Overheating the anode will not help any general purpose receiving tube. It will only make the gas problem worse and not help the loss of emission.
I borrowed the CRT zapper from the TV shop about once a year and shocked the picture tube back to life in my old 1957 vintage color TV (with a mid 60's vintage CRT in it). It worked by overheating the cathodes (about 8 or 9 volts on the 6.3 volt heaters), then discharging a cap between the cathode and all the other grids at the press of a button. As stated this ripped the worn out oxide layer off the top, exposing new material which had better emission. Occasionally it would create an cathode to G1 short which could often be cured with another push of the button. The CRT's heater voltage would then be returned to normal for several minutes and the emission readings taken again. The process could be repeated if there was no improvement.
Obviously this can't be done forever because the cathode will eventually be destroyed. I started with a free CRT pulled from a dead TV and kept it alive for 6 or 7 years, back in a time when color TV was rare and expensive.
The grid in a CRT is made of solid metal with a hole in it. It is physically stronger than the wire grids in a receiving tube, so the same process might be useful, but scaled down.
Some specialized tubes and many transmitting tubes can be "degassed" by overheating the anode, but they were designed this way. It has been reported that you can rejuvenate some receiving tubes by baking them in an oven, but I have not tried this.
I thought this was about last night's Dr Who (BBC America) story.
The usual explanation is that there should be a mono-atomic film of Barium on the surface of the oxide. This may "dry out" (evaporate). There's more Barium deep inside the oxide. Ideally this migrates to the surface about as fast as the surface evaporates. Sometimes it doesn't. Over-heating loosens-up the deep Barium so it diffuses to the surface faster.
I've heard of it, it was WIDELY done on TV sets, I have seen similar treatment techniques on Transmitter tubes but don't have a cite.
Of course we can't look inside a sealed tube so whether we "burn the surface" or "simmer the oxide" is a moot point.
In 1970s I rejuvenated old picture tubes by simply ramping up heater voltage. There were special 3-tap filament autotransformers for this purpose. The first tap was 7V, the second 8V, and the third 9V. After 9V does not help, the tube goes to trash. It was really helpful in extending CRT's life for 2-4 years, and I never had a 9V heater blowout.
As to rejuvenation, there are 10s of different recipies, which may or may not work. My favorite one is 2 min at 2x heater voltage followed by a prayer to St. Nicholas.
As to rejuvenation, there are 10s of different recipies, which may or may not work. My favorite one is 2 min at 2x heater voltage followed by a prayer to St. Nicholas.
A link discussing rejuvenation:
Valve Rejuvenation - UK Vintage Radio Repair and Restoration Discussion Forum
I wouldn't go the microwave route:
An experiment for gassy tubes
I read the chapter on getters again in RCA 1962 Electron Tube Design:
electron Tube Data sheets - RCA Documents
Page 522 summary point 3 seems to be the only substantiated aspect of using whatever available active getter flash material is still left to pull back any slightly gassy valve (ie. bias voltage in a cathode bias circuit starts to increase slightly over time as grid voltage rises above 0V, given that grid leak is acceptable value).
I was going to try to selectively heat the getter material to hopefully not too much more than 150-200C (to avoid contributing to other outgassing mechanisms) by getting a strong light source such as qu-Hal bulb to focus on the getter material only. If I use a large convex lens then that may also assist by filtering out low infra-red frequencies which the valve glass will be opaque to. For me, the test jig would be an amplifier push-pull output stage with independent cathode bias where the slightly gassy valve is just held to 50% or so of anode dissipation by a variac supply constraining heater and B+ voltage levels.
Valve Rejuvenation - UK Vintage Radio Repair and Restoration Discussion Forum
I wouldn't go the microwave route:
An experiment for gassy tubes
I read the chapter on getters again in RCA 1962 Electron Tube Design:
electron Tube Data sheets - RCA Documents
Page 522 summary point 3 seems to be the only substantiated aspect of using whatever available active getter flash material is still left to pull back any slightly gassy valve (ie. bias voltage in a cathode bias circuit starts to increase slightly over time as grid voltage rises above 0V, given that grid leak is acceptable value).
I was going to try to selectively heat the getter material to hopefully not too much more than 150-200C (to avoid contributing to other outgassing mechanisms) by getting a strong light source such as qu-Hal bulb to focus on the getter material only. If I use a large convex lens then that may also assist by filtering out low infra-red frequencies which the valve glass will be opaque to. For me, the test jig would be an amplifier push-pull output stage with independent cathode bias where the slightly gassy valve is just held to 50% or so of anode dissipation by a variac supply constraining heater and B+ voltage levels.
There are multiple possible problems and multiple "fixes".
As you and Tubelab say, K-G1 shorts happen. The best first fix is to fold a towel, put the CRT face down, and drop it a few inches a few times. Maybe the crap falls down to the CRT face, and will settle harmlessly at the bottom of the screen when you put it back in service. As Tubelab says, many of these heater over-heaters also had a ZAP function, which might burn-out stray crap. Aside from temporary cookers, there were boosters you put in the TV permanently (well, until the CRT quit completely). Like running your "tired" EL34 on 7.0V heat.
I would not fret a oxide-cathode tube in audio service that "read low emission". The max emission of an oxide cathode is far in excess of any real audio need. Over-use of the crude emissions testers can damage the cathode. The analyzer the OP described seems to be able to plot the tube's performance. Run it at typical voltages and see if you get expected currents. A big EL34 amp may peak well over 250mA for a small part of an audio cycle. But the average is probably under 100mA.
Well, let's not forget there is typically nothing to loose...the candidates we talk about are going into the trash bin otherwise...so we can experiment. And I am happy to do so, but need a bit guidance which program to run.
By the way: I can measure vacuum quality and its development as well. So, for sure a parameter to watch.
I started with an EL34 as I had them laying around. Not sure, if they are the best candidate.
So I used heater overheating to 9.45V for 2 min. Let them cool down. - Nothing happened really.
I used than a more aggressive mode three time with cooling times in between where you overheat the heater to 9.45V, set anode voltage to 250V and let the program have the tube emitting 250mA.
As described here : Roehren-Regenerier-Geraet_zum_Selberbauen (sorry, german, but maybe google translater does a decent job), I watched the tube to become a bit red, but stay dark red and not becomes bright red.
All grids and connections are normal pentode operation. I got the tube moving from 54% to 74% emission...vacuum is not so nice, but not sure how it looked upfront as I forgot to document this, will do with the next candidate...
I have read in the spreadsheets above that they want one to connect all grids to the anode...really ? As well g1 ?
By the way: I can measure vacuum quality and its development as well. So, for sure a parameter to watch.
I started with an EL34 as I had them laying around. Not sure, if they are the best candidate.
So I used heater overheating to 9.45V for 2 min. Let them cool down. - Nothing happened really.
I used than a more aggressive mode three time with cooling times in between where you overheat the heater to 9.45V, set anode voltage to 250V and let the program have the tube emitting 250mA.
As described here : Roehren-Regenerier-Geraet_zum_Selberbauen (sorry, german, but maybe google translater does a decent job), I watched the tube to become a bit red, but stay dark red and not becomes bright red.
All grids and connections are normal pentode operation. I got the tube moving from 54% to 74% emission...vacuum is not so nice, but not sure how it looked upfront as I forgot to document this, will do with the next candidate...
I have read in the spreadsheets above that they want one to connect all grids to the anode...really ? As well g1 ?
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Please read this: http://www.roehrentest.de/Gitterstrom und Vakuum_EN.pdf
Basically, using the vacuumfactor of Barkhausen by measuring grid current and anode current in relationship to each other.
By the way: All credits have to go to Helmut Weigl who designed the Roetester now in the 9. Generation...I guess he is doing this now for more than 15 years. I am not in any way related to him, I am just a customer of him who finally found the time to build the kit he is selling. Marvelous support by him, he makes sure the stuff will work as expected.
Basically, using the vacuumfactor of Barkhausen by measuring grid current and anode current in relationship to each other.
By the way: All credits have to go to Helmut Weigl who designed the Roetester now in the 9. Generation...I guess he is doing this now for more than 15 years. I am not in any way related to him, I am just a customer of him who finally found the time to build the kit he is selling. Marvelous support by him, he makes sure the stuff will work as expected.
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Greetings to Blitz and the forum.
Back when I first started out as a "wireless mechanic" in the middle of another century, ordinary folks could often barely afford new valves for their radios, my then boss used his Lazarus machine to save the customer the cost of replacement. Of course, they had to buy new ones a couple of years on anywho, so the boss was the real winner as the service charge was made twice for the same fault.
This is the set up. Basically you connect your valves heater to one variable voltage supply, capable of 3 × nominal heater rating, and another supply variable up to say, 30v, negative to the the cathode, and positive through a lamp to the grid (to restrict the current through the delicate grid wires), the lamp being rated 28v at 50mA (about 60 ohms cold).
The method is, run the valves heater at its nominal voltage for a few minutes to warm it up and to prevent thermal shock, then, take it to 2 × nominal, and ramp up the cathode/grid supply until an even blue glow is seen around those electrodes (it's often possible to see this happen through holes that are in the anode, or through the mica's. If the whole valve glows its probably just gassy). If the glow doesn't appear, then take the heater voltage to 3× and try again. Some, notably the larger power types also need a higher bias on the grid/cathode, small signal ones, a bit less.
THEN, WHEN THE BLUE GLOW APPEARS, QUICKLY SWITCH OF THE HEATER POWER LEAVING
THE VALVE CATHODE TO COOL WITH THE CATHODE/GRID SUPPLY STILL POWERED UP.
It doesn't seem to work at all with power rectifier valves, perhaps they run so much current in use that their cathodes are kept "clean" until they becomes completely knackered, though signal diodes do seem to respond well.
I've found this successful with tired valves of both directly and indirectly heated types, as well as ones that have become lazy with lack of use, ie. used pulls out of the junk box. It's success rate I've found to be about 80% for an acceptable lasting improvement, provided it has NOT been tried before! Remember, it is a form of thermionic abuse and weaklings will die. Trying the process repeatedly on the same example will also destroy the valve, so if you get 50% emission back after one pass, accept it, and don't be tempted to give it one for luck.
BTW....I remember the Blitz
Cheers, Norman.
Back when I first started out as a "wireless mechanic" in the middle of another century, ordinary folks could often barely afford new valves for their radios, my then boss used his Lazarus machine to save the customer the cost of replacement. Of course, they had to buy new ones a couple of years on anywho, so the boss was the real winner as the service charge was made twice for the same fault.
This is the set up. Basically you connect your valves heater to one variable voltage supply, capable of 3 × nominal heater rating, and another supply variable up to say, 30v, negative to the the cathode, and positive through a lamp to the grid (to restrict the current through the delicate grid wires), the lamp being rated 28v at 50mA (about 60 ohms cold).
The method is, run the valves heater at its nominal voltage for a few minutes to warm it up and to prevent thermal shock, then, take it to 2 × nominal, and ramp up the cathode/grid supply until an even blue glow is seen around those electrodes (it's often possible to see this happen through holes that are in the anode, or through the mica's. If the whole valve glows its probably just gassy). If the glow doesn't appear, then take the heater voltage to 3× and try again. Some, notably the larger power types also need a higher bias on the grid/cathode, small signal ones, a bit less.
THEN, WHEN THE BLUE GLOW APPEARS, QUICKLY SWITCH OF THE HEATER POWER LEAVING
PHP:
It doesn't seem to work at all with power rectifier valves, perhaps they run so much current in use that their cathodes are kept "clean" until they becomes completely knackered, though signal diodes do seem to respond well.
I've found this successful with tired valves of both directly and indirectly heated types, as well as ones that have become lazy with lack of use, ie. used pulls out of the junk box. It's success rate I've found to be about 80% for an acceptable lasting improvement, provided it has NOT been tried before! Remember, it is a form of thermionic abuse and weaklings will die. Trying the process repeatedly on the same example will also destroy the valve, so if you get 50% emission back after one pass, accept it, and don't be tempted to give it one for luck.
BTW....I remember the Blitz
Cheers, Norman.
Greetings to Blitz and the forum.
BTW....I remember the Blitz
Cheers, Norman.
As a young lad I remember black and white TV's.
Ours packed up and from a stack of old used valves I replaced the valves one by one until it started working again.
I must have been about 12 then so a completely stupid and dangerous thing to do. I am surprised I lived this long.
We had an old Radiogram and I was always fascinated by the magic eye.
When it finally died my mother let me strip it down for scrap.
If I remember correctly, the manufacturing process was something like this:
Apply the vacuum pump, and pump the tube down; then use RF heating on the plate to get it to outgas, and continue the vacuum pump.
Then the glass opening to the vacuum pump was sealed, and the pump removed.
Lastly the getter pan(s) were heated with RF to get them to flash.
I believe that most restoration processes were to fix either the cathode, or the Direct Heating filament emission.
I think most of my power tubes run at about 190 to 240 degrees. I am not sure how well 'activating' the getter will work.
When I get a gassy tube, it either goes into the garbage, or it goes on the museum display board.
Apply the vacuum pump, and pump the tube down; then use RF heating on the plate to get it to outgas, and continue the vacuum pump.
Then the glass opening to the vacuum pump was sealed, and the pump removed.
Lastly the getter pan(s) were heated with RF to get them to flash.
I believe that most restoration processes were to fix either the cathode, or the Direct Heating filament emission.
I think most of my power tubes run at about 190 to 240 degrees. I am not sure how well 'activating' the getter will work.
When I get a gassy tube, it either goes into the garbage, or it goes on the museum display board.
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