811A VTTC
EEYORE, Sun Feb 12 2006, 08:56PMHello all,
on a whim, i bought an 811A JAN vacuum tube by Cetron. I need some help with calculating the values i need for the various parts such as grid leak components and all...I plan to run it with a MOT via a variac as to not overpower, nor overvolt it. How do i calculate the various resistors and capacitors needed?I may have 2 CDE Mica caps coming rated for 5000vac .001uF. I assume the tuning goes the same as with a standard coil?How do i calcuate the feedback coil?
Lotsa Qs, i know
Thanks!
Matt
Re: 811A VTTC
HV Enthusiast, Sun Feb 12 2006, 09:35PM
Steve Ward has already done a design for dual 811As. You could use his values as a starting point and modify from there.
Here is his webpage:
http://www.stevehv.4hv.org/VTTC1.htm
HV Enthusiast, Sun Feb 12 2006, 09:35PM
Steve Ward has already done a design for dual 811As. You could use his values as a starting point and modify from there.
Here is his webpage:
http://www.stevehv.4hv.org/VTTC1.htm
Re: 811A VTTC
..., Wed Feb 15 2006, 08:25AM
I made a single 811a mini coil using that exact tube :)
Instead of typing everything twice, I will refer you to my projects thread where the information is.
..., Wed Feb 15 2006, 08:25AM
I made a single 811a mini coil using that exact tube :)
Instead of typing everything twice, I will refer you to my projects thread where the information is.
Re: 811A VTTC
EEYORE, Wed Feb 15 2006, 08:21PM
Nice!Looks exactly what im looking for...A small coil to "play" with...With all my others being so dangerous, id like something more controllable....So i thought the 811a was rated for max 1500volts?
Heres what I have:
2700volt MOT Plan to use a variac to control this to 1500vac...
6.3volt 4 amp filament xfmr...
811a tube-Need to get a socket...
1.3nF 10kv cermic capacitor(quite large!)
Just need to amass some resistors and some ceramic bypass capacitors.
I plan to wind a smal secondary. I got a 6in spool of free magnet wire from Essex
Just for asking nicely...
Matt
EEYORE, Wed Feb 15 2006, 08:21PM
Nice!Looks exactly what im looking for...A small coil to "play" with...With all my others being so dangerous, id like something more controllable....So i thought the 811a was rated for max 1500volts?
Heres what I have:
2700volt MOT Plan to use a variac to control this to 1500vac...
6.3volt 4 amp filament xfmr...
811a tube-Need to get a socket...
1.3nF 10kv cermic capacitor(quite large!)
Just need to amass some resistors and some ceramic bypass capacitors.
I plan to wind a smal secondary. I got a 6in spool of free magnet wire from Essex
Just for asking nicely...
Matt
Re: 811A VTTC
..., Thu Feb 16 2006, 01:20AM
I have extra 811a sockets/top caps... They are not the twist lock kind, just spring clips for the pins; but work great. Also have extra 4k resistors and 2.2nf bypass caps...
I wouldn't worry about turning down the mot voltage; I have run the tube you have at >4kv and it didn't even think of arking over. Although if you are using that large of a tank cap you are going to need to turn down the power to keep the pate dissipation safe. 0.6nf at 2.2kv was just about right for the tube to glow a nice orange color throughout the plate... I guess that running it off a lower voltage would allow you to do short runs at a higher power and then turn it down for the longer runs, or add a stattco and run at high power all of the time...
I like my 811a coil because the streamers are so benign, they are almost silent, and you can touch them!
Good luck!
..., Thu Feb 16 2006, 01:20AM
I have extra 811a sockets/top caps... They are not the twist lock kind, just spring clips for the pins; but work great. Also have extra 4k resistors and 2.2nf bypass caps...
I wouldn't worry about turning down the mot voltage; I have run the tube you have at >4kv and it didn't even think of arking over. Although if you are using that large of a tank cap you are going to need to turn down the power to keep the pate dissipation safe. 0.6nf at 2.2kv was just about right for the tube to glow a nice orange color throughout the plate... I guess that running it off a lower voltage would allow you to do short runs at a higher power and then turn it down for the longer runs, or add a stattco and run at high power all of the time...
I like my 811a coil because the streamers are so benign, they are almost silent, and you can touch them!
Good luck!
Re: 811A VTTC
EEYORE, Thu Feb 16 2006, 02:03AM
Hmmm....Interesing about the voltage...
Im using a large capacitor simplyb/c its all i have
....I wonder if an MMC would suffice?I could series some Film/Foil caps.They are physcially large as well...Wima...
Ill PM you about the sockets...
Matt
EEYORE, Thu Feb 16 2006, 02:03AM
... wrote ...
I have extra 811a sockets/top caps... They are not the twist lock kind, just spring clips for the pins; but work great. Also have extra 4k resistors and 2.2nf bypass caps...
I wouldn't worry about turning down the mot voltage; I have run the tube you have at >4kv and it didn't even think of arking over. Although if you are using that large of a tank cap you are going to need to turn down the power to keep the pate dissipation safe. 0.6nf at 2.2kv was just about right for the tube to glow a nice orange color throughout the plate... I guess that running it off a lower voltage would allow you to do short runs at a higher power and then turn it down for the longer runs, or add a stattco and run at high power all of the time...
I like my 811a coil because the streamers are so benign, they are almost silent, and you can touch them!
Good luck!
I have extra 811a sockets/top caps... They are not the twist lock kind, just spring clips for the pins; but work great. Also have extra 4k resistors and 2.2nf bypass caps...
I wouldn't worry about turning down the mot voltage; I have run the tube you have at >4kv and it didn't even think of arking over. Although if you are using that large of a tank cap you are going to need to turn down the power to keep the pate dissipation safe. 0.6nf at 2.2kv was just about right for the tube to glow a nice orange color throughout the plate... I guess that running it off a lower voltage would allow you to do short runs at a higher power and then turn it down for the longer runs, or add a stattco and run at high power all of the time...
I like my 811a coil because the streamers are so benign, they are almost silent, and you can touch them!
Good luck!
Hmmm....Interesing about the voltage...
Im using a large capacitor simplyb/c its all i have
....I wonder if an MMC would suffice?I could series some Film/Foil caps.They are physcially large as well...Wima...Ill PM you about the sockets...
Matt
Re: 811A VTTC
..., Thu Feb 16 2006, 03:04AM
pm replied too...
The ideal thing for you to do would put 2 of the caps you have in series, but if you only have one then that won't work...
Probably the next easiest thing would be to buy one (here is a cheap source)
I wouldn't recomend a mmc type thing, the tank cap seems to be quite critical to correct operation. I tried replacing the 650pf one I had with a string of 3 2.2nf ceramics and the coil didn't even want to oscillate
..., Thu Feb 16 2006, 03:04AM
pm replied too...
The ideal thing for you to do would put 2 of the caps you have in series, but if you only have one then that won't work...
Probably the next easiest thing would be to buy one (here is a cheap source)
I wouldn't recomend a mmc type thing, the tank cap seems to be quite critical to correct operation. I tried replacing the 650pf one I had with a string of 3 2.2nf ceramics and the coil didn't even want to oscillate
Re: 811A VTTC
EEYORE, Thu Feb 16 2006, 04:42AM
I think i will try what i have before buying any capacitors...Im only using one 811a tube, so the power level wont rise too much....I think the plate can only take like 100ma or so?
Matt
EEYORE, Thu Feb 16 2006, 04:42AM
I think i will try what i have before buying any capacitors...Im only using one 811a tube, so the power level wont rise too much....I think the plate can only take like 100ma or so?
Matt
Re: 811A VTTC
..., Thu Feb 16 2006, 06:27AM
I believe they are good for 120ma continuous anode current, but in a vttc there is only current passing like 1/4 of the time...
I have not taken measurements for plate current yet, but I know that the tank current in my coil is almost 600a unloaded and 200a with streamers I see why a good tank cap is so important now...
Back to the original questions of how to calculate the feedback; so far as I can tell you can't. Just stick to around 20 turns (I found 18 works good for mine by having the tube ark over at the metal/glass seal between grid/cathode on the outside of the tube with 20 turns at 4.5kv, so I removed 2 turns and it hasn't happened since...)
For the tank cap; mica caps should be good but I do not know. I do that the doorknob caps sold by hrhdavid on ebay do work.
..., Thu Feb 16 2006, 06:27AM
I believe they are good for 120ma continuous anode current, but in a vttc there is only current passing like 1/4 of the time...
I have not taken measurements for plate current yet, but I know that the tank current in my coil is almost 600a unloaded and 200a with streamers
I see why a good tank cap is so important now...Back to the original questions of how to calculate the feedback; so far as I can tell you can't. Just stick to around 20 turns (I found 18 works good for mine by having the tube ark over at the metal/glass seal between grid/cathode on the outside of the tube with 20 turns at 4.5kv, so I removed 2 turns and it hasn't happened since...)
For the tank cap; mica caps should be good but I do not know. I do that the doorknob caps sold by hrhdavid on ebay do work.
Re: 811A VTTC
EEYORE, Thu Feb 16 2006, 05:56PM
Boy does that tube get HOT, just the filament...
I put on 12 turns of wire for the feedback(i ran out), and used a 3.3kohm10watt resistor for the grid. Nothing got warm but the MOT, 811a, and the primary. The tank cap stays cold actually....
Kinda strange thing happens-When i crank the variac to close to 75% the sparks get big(2.5inches) but then fade out quickly.Any ideas?
Plate gets red rather quickly as well....
Now that i see it works, i will have to build a proper setup for it
EEYORE, Thu Feb 16 2006, 05:56PM
... wrote ...
I believe they are good for 120ma continuous anode current, but in a vttc there is only current passing like 1/4 of the time...
I have not taken measurements for plate current yet, but I know that the tank current in my coil is almost 600a unloaded and 200a with streamers I see why a good tank cap is so important now...
Back to the original questions of how to calculate the feedback; so far as I can tell you can't. Just stick to around 20 turns (I found 18 works good for mine by having the tube ark over at the metal/glass seal between grid/cathode on the outside of the tube with 20 turns at 4.5kv, so I removed 2 turns and it hasn't happened since...)
For the tank cap; mica caps should be good but I do not know. I do that the doorknob caps sold by hrhdavid on ebay do work.
I tried a quick lashup last night....Got 1.5inchers...I believe they are good for 120ma continuous anode current, but in a vttc there is only current passing like 1/4 of the time...
I have not taken measurements for plate current yet, but I know that the tank current in my coil is almost 600a unloaded and 200a with streamers
I see why a good tank cap is so important now...Back to the original questions of how to calculate the feedback; so far as I can tell you can't. Just stick to around 20 turns (I found 18 works good for mine by having the tube ark over at the metal/glass seal between grid/cathode on the outside of the tube with 20 turns at 4.5kv, so I removed 2 turns and it hasn't happened since...)
For the tank cap; mica caps should be good but I do not know. I do that the doorknob caps sold by hrhdavid on ebay do work.
Boy does that tube get HOT, just the filament...
I put on 12 turns of wire for the feedback(i ran out), and used a 3.3kohm10watt resistor for the grid. Nothing got warm but the MOT, 811a, and the primary. The tank cap stays cold actually....
Kinda strange thing happens-When i crank the variac to close to 75% the sparks get big(2.5inches) but then fade out quickly.Any ideas?
Plate gets red rather quickly as well....
Now that i see it works, i will have to build a proper setup for it
Re: 811A VTTC
Vaxian, Wed Apr 11 2007, 07:40AM
That happens allot with VTTC's (nice sparks, then they deminish)
Something is getting hot I suspect. Have you checked the grid leak resistor? 10 Watts sounds a bit underrated to me. I know all about the use what you got method though, don't think I am getting critical, just making suggestions.
Do you have a topload at all? A topload can improve a VTTC quite a bit. Something small, around 3" for a 3" OD secondary. I can suggest an El-cheapo hardware store topload if you like, or see some of my other posts.
Look forward to seeing how your coil progresses, I am deep into VTTC country myself, just started my second, don't know which tube I'm going to use yet but already started the power supply & grid leak mounting.
Good luck, will watch for further posts about your coil, & pics?
Dan
Vaxian, Wed Apr 11 2007, 07:40AM
That happens allot with VTTC's (nice sparks, then they deminish)
Something is getting hot I suspect. Have you checked the grid leak resistor? 10 Watts sounds a bit underrated to me. I know all about the use what you got method though, don't think I am getting critical, just making suggestions.
Do you have a topload at all? A topload can improve a VTTC quite a bit. Something small, around 3" for a 3" OD secondary. I can suggest an El-cheapo hardware store topload if you like, or see some of my other posts.
Look forward to seeing how your coil progresses, I am deep into VTTC country myself, just started my second, don't know which tube I'm going to use yet but already started the power supply & grid leak mounting.
Good luck, will watch for further posts about your coil, & pics?
Dan
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