Dear Folks,
I have some small signal russian NOS tubes ( 6N1P,6N2P,6N6P,6N14P ... ) and would like to use them for small audio projects. In some articles out in the space I read that it is mandatory to "burn-in" alls NOS tubes before use. The reason why to do this is mostly a little bit mystic for me. Someone told: [FONT=ARIAL, HELVETICA]"[/FONT][special=[FONT=ARIAL, HELVETICA]a certain amount of the gases trapped in its materials is "leached" out into the vacuum of the tube]%[/special]"
[/FONT] The procedure to inspire a tube is fairly complex and take several days. First increase heater voltage over serveral hours/days, grounding grid and no HT voltage. After that do the same with HT voltages and heated tube, grounded grid. At least run the tube a few days/hour well biased but no signal.
I would like to ask you if this is realy necessary or it´s one of the mystic things round about tubes?
Best regards
Karsten
I have some small signal russian NOS tubes ( 6N1P,6N2P,6N6P,6N14P ... ) and would like to use them for small audio projects. In some articles out in the space I read that it is mandatory to "burn-in" alls NOS tubes before use. The reason why to do this is mostly a little bit mystic for me. Someone told: [FONT=ARIAL, HELVETICA]"[/FONT][special=[FONT=ARIAL, HELVETICA]a certain amount of the gases trapped in its materials is "leached" out into the vacuum of the tube]%[/special]"
[/FONT] The procedure to inspire a tube is fairly complex and take several days. First increase heater voltage over serveral hours/days, grounding grid and no HT voltage. After that do the same with HT voltages and heated tube, grounded grid. At least run the tube a few days/hour well biased but no signal.
I would like to ask you if this is realy necessary or it´s one of the mystic things round about tubes?
Best regards
Karsten
Hi!
I don't see a need for a special procedure to burn in tubes. I use many NOS tubes. They do burn in and improve after a while, but I do that in the actual amp.
I would discourage a burn in procedure with heater voltage and no plate voltage for indirectly heated tubes. Many indirectly heated tubes can develop a interface layer when they are operated without plate current unless they are designed for that.
If you insist on a burn in, I would use the nominal heater voltage and start with a low plate voltage and increase that step by step, but don't run them without plate voltage.
Best regards
Thomas
I don't see a need for a special procedure to burn in tubes. I use many NOS tubes. They do burn in and improve after a while, but I do that in the actual amp.
I would discourage a burn in procedure with heater voltage and no plate voltage for indirectly heated tubes. Many indirectly heated tubes can develop a interface layer when they are operated without plate current unless they are designed for that.
If you insist on a burn in, I would use the nominal heater voltage and start with a low plate voltage and increase that step by step, but don't run them without plate voltage.
Best regards
Thomas
For noval tubes, I bake them in an oven at 350F for four hours, and allow to cool before using.
Prior to this I just plugged them in and ran them. I experienced several failures (6F4P specifically). Since baking them I have experienced no failures.
The theory behind this procedure is that heating them helps to activate the getter to remove trace gasses.
ymmv.
Prior to this I just plugged them in and ran them. I experienced several failures (6F4P specifically). Since baking them I have experienced no failures.
The theory behind this procedure is that heating them helps to activate the getter to remove trace gasses.
ymmv.
Morgan Jones suggests an oven bake and has some data to back that up. I run the heaters for an hour or so, then apply plate voltage. That's not long enough to poison the cathode (a real issue) but long enough to get everything nice and warm and encourage outgassing and gettering.
Nothing wrong at all with what Thomas suggests, and it may even be theoretically better, it's just a bit of a PITA.
Nothing wrong at all with what Thomas suggests, and it may even be theoretically better, it's just a bit of a PITA.
Try running them whit some alummina foil over them. to make sure the getter spot gets Hot
A lot of tubes are just burned in at the factory whit AC on the tube and a lightbulb to limit the current. Works fine and keeps the equipement used simple.
cathode activity on poor tubes can be brought back to usable if you run the heaters Hot (not only for thorium coated tubes)
V4lve.
A lot of tubes are just burned in at the factory whit AC on the tube and a lightbulb to limit the current. Works fine and keeps the equipement used simple.
cathode activity on poor tubes can be brought back to usable if you run the heaters Hot (not only for thorium coated tubes)
V4lve.
Hi all,
Thank you for your comments and knowledge.
For my little understanding of physics and chemical reactions the getter should do all things well. After manufactoring the getter absorbes any gas influence of the vacuum. This can only be some rest of gas inside the tube, gas particles from internal structure ( desoprtion ) or very small ( a few molecules ) from outside of the tube ( permeation ). So far I understand all relevant gas parts of internal material is set free by heating the tube extremly while evacuate ( create vacuum ) on manufacturing. Fireing the getter later will bind the rest of gas. All tubes, especial the military ones, are burned in to verify thier parameters.
For that I see no really physical reason why a NOS tube should burned in. Nevertheless I will run the tubes in circuit for 24h to reach the operating temeratur of all components and measure if I inside the given parameters.
Thanks a lot for this enlighting discussion.
Karsten
Thank you for your comments and knowledge.
For my little understanding of physics and chemical reactions the getter should do all things well. After manufactoring the getter absorbes any gas influence of the vacuum. This can only be some rest of gas inside the tube, gas particles from internal structure ( desoprtion ) or very small ( a few molecules ) from outside of the tube ( permeation ). So far I understand all relevant gas parts of internal material is set free by heating the tube extremly while evacuate ( create vacuum ) on manufacturing. Fireing the getter later will bind the rest of gas. All tubes, especial the military ones, are burned in to verify thier parameters.
For that I see no really physical reason why a NOS tube should burned in. Nevertheless I will run the tubes in circuit for 24h to reach the operating temeratur of all components and measure if I inside the given parameters.
Thanks a lot for this enlighting discussion.
Karsten
excuse me. i didnt realize the economic depression was that bad for bald people
No jokes. the alumina foil reflects the heat back inwards. and its a good way to heat up the inside parts.
For the real freaks you could make a little 1KW induction heater and re-flash the getter on poor tubes
V4lve
No jokes. the alumina foil reflects the heat back inwards. and its a good way to heat up the inside parts.
For the real freaks you could make a little 1KW induction heater and re-flash the getter on poor tubes
V4lve
Hi,
There is no real usefull difference which side of aluminium foil you use. Only temperatures higher than 500°C will have verry small effects. Furthermore the cooling effect of convection is much higher than the refelction factor of heat radiation. If you want to overheat your tube you should envelope it with something like rockwool.
Fireing/re-fresh the getter? If you overheat the internal material of a tube after initial fiering the getter you risk degassing. Otherwise the getter was already fired and condensed inside the tube. You can only heat the condesed part of the getter. What should this do?
There is no real usefull difference which side of aluminium foil you use. Only temperatures higher than 500°C will have verry small effects. Furthermore the cooling effect of convection is much higher than the refelction factor of heat radiation. If you want to overheat your tube you should envelope it with something like rockwool.
Fireing/re-fresh the getter? If you overheat the internal material of a tube after initial fiering the getter you risk degassing. Otherwise the getter was already fired and condensed inside the tube. You can only heat the condesed part of the getter. What should this do?
Can you elaborate on this? I have some 6C33's and GM70's I plan on using in future projects.
Not exactly. Used getter cups still contain barium Be-course They use MORE Barium than necessary en order to make sure all oxygen is absorbed. when all the air is removed the reaction stops this does not imply no barium metal is left in the getter
You cannot Heat the condensed part of the getter whit induction heating Be course thats a SALT
Metallic barium reacts whit a non metal makes it a salt reaction.
You can however heat the getter of any tube if there is still a good reserve of barium metal. it will flash again.
V4lve.
I've had no problem with GM70, either graphite or copper. I find they are relatively stable and only need minor bias adjustments during the first hours of operation. (1kV/120mA operation)
Long ago I designed a very bad OTL amplifier around 6C33, my biggest design failure..
I subsequently learned that running them in a test jig with just filament power for day or so then running them at 15 - 20W dissipation for another day or three helped a lot.. There are a couple of members with extensive applications experience with the 6C33.. Search on 6C33 and OTL here..I have avoided the 6C33 (well more truthfully lost interest in it) since the OTL debacle back in 1998.
Have to say I have heard some very good sounding SE amps designed around the 6C33 in the past so definitely worth the effort.
you can read thru these threads.....
http://www.diyaudio.com/forums/tubes-valves/137009-6c33c-b-pp-se.html
http://www.diyaudio.com/forums/tubes-valves/188076-6c33-ready-set-go.html
http://www.diyaudio.com/forums/tubes-valves/9630-otl-continued.html
http://www.diyaudio.com/forums/tubes-valves/186074-6c33.html
Recently I took 2 tubes - completely NOS.
Tung-Sol 6485 small signal true pentode, aka 6AH6.
Fresh from their boxes, each stamped APR 1972 38.
Set-up with IR-LED at the cathode 1.14 volts, G1 grounded thru 100 kohm, G2 at 110 volts, G3 tied to cathode, plate connected to 195 volts thru 12 kohm.
Monitored plate voltage for the 1st 4 hours in the life of these tubes:
#1: Vp started out at 135 volts, gradually dropped to 95 volts.
apparently Ip rose from 5 to 8.3 mA.
#2: Vp started out at 165 volts, over time dropped to 105 volts.
apparently Ip rose from 2.5 to 7.5 mA.
Both changed rapidly after turn-on, rate of change dropped considerably after 10 mins or so, but clearly went on for hours.
Tung-Sol 6485 small signal true pentode, aka 6AH6.
Fresh from their boxes, each stamped APR 1972 38.
Set-up with IR-LED at the cathode 1.14 volts, G1 grounded thru 100 kohm, G2 at 110 volts, G3 tied to cathode, plate connected to 195 volts thru 12 kohm.
Monitored plate voltage for the 1st 4 hours in the life of these tubes:
#1: Vp started out at 135 volts, gradually dropped to 95 volts.
apparently Ip rose from 5 to 8.3 mA.
#2: Vp started out at 165 volts, over time dropped to 105 volts.
apparently Ip rose from 2.5 to 7.5 mA.
Both changed rapidly after turn-on, rate of change dropped considerably after 10 mins or so, but clearly went on for hours.
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