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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Today i got a nice little vacuum tube pentode from a thrown out television. It is nice, and the plate is bigger than the 811a, even though the bulb is much smaller. It is pretty incredible, the plate is 990 volts and 1.4 amps!! The tube is 36mc6. The plate dissapation is only 33 watts though, while 811a is 65 iirc. I am going to use the 811a schematic from Steve Ward, and probably run this thing CW considering its high plate voltage. I currently have the transformers from the television in the oven to dry out if it is wet, and i will just have to use my 4 inch secondary 'till i get some wire for a new secondary. I have a small 1 inch secondary that i might use, but it only has about 300-500 turns.
Time to go work on it some.
Update: Well, plate current is 125ma max. I don't know what i was thinking. Average cathode current is 1400ma. So, what does that mean?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
36mc6 has the same specifications as 6LQ6 except for the heater, which is a 36V series connection type, whilst 6LQ6 has a 6.3V heater for parallel connection. (There is a full form data sheet for 6LQ6 at Frank's)
I think you may have confused the maximum 'plate supply voltage' with the actual working anode/plate voltage itself which is very much lower at around 175V.
I don't know where your data sheet came from, but it seems to be a much shortened copy. 1200mA is the maximum peak current which the valve can tolerate in pulse operation. The average input power to the valve is 30W.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Harry wrote ...
36mc6 has the same specifications as 6LQ6 except for the heater, which is a 36V series connection type, whilst 6LQ6 has a 6.3V heater for parallel connection. (There is a full form data sheet for 6LQ6 at Frank's)
I think you may have confused the maximum 'plate supply voltage' with the actual working anode/plate voltage itself which is very much lower at around 175V.
I don't know where your data sheet came from, but it seems to be a much shortened copy. 1200mA is the maximum peak current which the valve can tolerate in pulse operation. The average input power to the valve is 30W.
Omg, wth? Dude.... You seem to be correct, but this place that i got the datasheet from must be soooo full of it. Look at the link in my first post. It says that under typical operation it is 175 volts and 125ma, like you said. But, under characteristics and typical operation, it says all this: Hortz Defl Amplifier DC Plate Supply Voltage ....................... 990 V Peak Positive-Pulse Plate Voltage ............. 750 V Peak Negative-Pulse Plate Voltage ............. -1100 V DC Grid No. 3 Voltage ......................... 250 V DC Grid No. 2 Voltage ......................... -330 V Peak Negative-Pulse Grid No. 1 Voltage ........ 400 V Average Cathode Current ....................... 1400 mA
Average cathode current is 1.4 amps? Cant be. DC plate supply voltage is 990 volts. That disagrees with the 175 volt plate rating.
So i don't understand. Either way, i am going to run it just like an 811a with a mot running on maybe 30-60 volts in.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Definitely something funny about that data.
TV sweep tubes were also used in audio amps and RF linear amps, typically running off something like 600V plate supply and 250V screen supply. These would be good values to shoot for if building a VTTC.
You won't be copying Ward's schematic exactly because this tube is a beam tetrode whereas the 811A is a triode. You need to figure out what to do with the screen grid. Connecting it to the plate is not a good idea, and connecting the two grids together may not be too smart either.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Here is a circuit diagram/schematic for a VTTC using the deflection valve/sweep tube PL504, which would need only small changes to use it with your valve
If you Google "PL504 VTTC" and "PL504 Tesla" you'll find all sorts of stuff about using these pentodes as Tesla coil exciters.
Remember that Line Output valves are designed for pulse operation only - generally pulses not exceeding 18 microseconds - so all figures in the data sheets assume the user will be running the valve in pulse mode.
European users with 230V mains can do without an HT transformer altogether by using a voltage doubler using high voltage electrolytics, provided always that you are comfortable and confident using potentially dangerous 'live chassis' techniques. (Best to use an isolation transformer if you have one!)
Other suitable European valves, besides PL504, are PL500, PL509 and PL519, though their prices have risen after their discovery by audio enthusiasts.
Here is a sweep tube VTTC design using PL519 by Vladimiro Mazzilli of ZVS fame:
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Well, i just hooked it up yesterday for a run, and i tied all the grids together. It worked ok, it would light a fluorescent bulb up very brightly, and it had ok breakout, but then i found that my mot was shorted. It has been for awhile. I am about to go do some changes, and see what i get.
Update: Well, i tried it again, and it arced over. Tube must have a leak. The tube was not touching anything while on, or off, but it arced. End of this project ._.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hmm, I just found one of these valves too!
Looks intact, perhaps the secret is to "cook" the valve as mentioned in Electronics World to remove some of the gas from inside before running it at max voltage so it doesen't arc over.
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Vacuum Tube Tesla Coil with Horizontal Output Tube.
