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Vacuum tubes with 117v filaments for VTTC

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Weston

Thu Mar 19 2009, 04:48AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

For a project I want to make a very tiny VTTC, however, a large space is taken up by the filament transformer. I have decided to try to use a tube with a 117v filament. Are any tubes with 117 v filaments suitable for radio frequency at a few watts. I was thinking of the 117N7, would this work? Any suggestions?

Tonskulus

Thu Mar 19 2009, 09:22AM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

I don't know if there is any tube with 117V filaments. Some bigger P-serie tubes (like PL519 etc) has around 50V filament voltage as those p-series are all rated 300mA standard filament current. Why dont you just tear apart cellphone charger and use its PCB as filament supply? Those smps style chargers are really tiny. There might be enough power for filaments of tiny tube.

Fabio

Thu Mar 19 2009, 10:53AM

Registered Member #122 Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148

For my plasma cigarette lighter i use one PL509 tube with heater directly powered with mains (230V-50Hz) with a 5uF 400Vac capacitor in series.

Of course, since you have a different voltage, frequency and a different tube you need a different capacitor, but calculating them is quite easy (think about the capacitive reactance formulas and resistive voltage divider formulas and merge them)

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EDIT:
I also use rectified mains for grid bias and doubled mains for plate voltage, a true transformerless design!

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Ciao !
Fabio.

Littlew

Thu Mar 19 2009, 06:58PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

you can use small 220-6.3/12 ferrite transformer. Today, there is MANY good electric transformers.
Also you can use rewinded transformers for halogen blubs it produce 12v @ ~15A , inside that transformer simple autogenerated half bridge and ferrite transformer.
i powered with that transformer GU-34b(for filiament test around 1 hour)

Proud Mary

Thu Mar 19 2009, 10:22PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi Weston,

what is "very tiny" son?

Don't even think about 117N7 - its a tetrode/diode rectifier twin package on a big octal base., and only has an ouput of 1W2.

Tell us what "very tiny" is, put the circuit diagram (schematic) up here, and who knows, I might just stake you to a good, powerful little valve if I don't think it's going to be wasted.

Weston

Thu Mar 19 2009, 11:43PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

I am basing my design from the schematic posted here: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?64252 I am building it to be as small as possible. I want to be able to easily bring it into school and other places for demonstrations, and have it on my desk when I am not bringing it anywhere (my previous coil was about half a meter square, not including the secondary). That means no transformers, that's why I want the tube to have a 117v filament. B+ will be doubled line voltage. I plan to have all components mounted on the base of the tube. The secondary, primary and feedback will be mounted on a form that will go over the tube.

LithiumLord

Fri Mar 20 2009, 01:38PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

You can try a TSD-990 or alike transformer - the whole PSU device will not be any big (the like 1.5cm/side cube of the xformer and a single DIP8 driver IC beneath, along with just a couple of other parts).

Dr. Dark Current

Fri Mar 20 2009, 03:17PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Fabio wrote ...

For my plasma cigarette lighter i use one PL509 tube with heater directly powered with mains (230V-50Hz) with a 5uF 400Vac capacitor in series.

I wouldn't do that, because when you turn it on just at the "right" time, the filament can get the full peak voltage across it (330V), it'll "tick" and the fun is over.

Tonskulus

Fri Mar 20 2009, 03:51PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Dr. Kilovolt wrote ...

Fabio wrote ...

For my plasma cigarette lighter i use one PL509 tube with heater directly powered with mains (230V-50Hz) with a 5uF 400Vac capacitor in series.

I wouldn't do that, because when you turn it on just at the "right" time, the filament can get the full peak voltage across it (330V), it'll "tick" and the fun is over.

PTC resistor in series will prevent this situation.

Weston

Fri Mar 20 2009, 11:30PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

So should I just use a PL509 tube and a capacitive ballast? I think I have some PTC resistors in my part bin....

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