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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS27-Tube VCA question
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Sun Jun 21, 2009 7:15 pm    Post subject: CGS27-Tube VCA question Reply with quote  Mark this post and the followings unread

Hey all

My question is in regards to CGS 27 Tube VCA and how to get 6V to the heater of the tube. I'm guessing that a voltage divider would be the easiest way to scale down the 15V to the 6V that i need.

The problem is i'm not too sure what value resisters to use as (i'm guessing) i need to supply enough current to the heater.... i worked it out to be a ratio of 0.4, so 4k and 6k resistors??

Any help on the matter would be great,

Thanks all ,Luke
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slacker



Joined: Nov 18, 2007
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Location: England
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PostPosted: Mon Jun 22, 2009 10:45 am    Post subject: Reply with quote  Mark this post and the followings unread

You don't need a voltage divider. You can do it with just a resistor from +15 to the heater, the heater itself then acts like the bottom resistor in the divider.
To do this you need to know how much current the heater draws. Then pick your resistor so it will drop 9 volts at that current, the heater will then drop the remaining 6 volts. You'll also need to make sure your resistor is rated at a high enough wattage for the current.
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hobgob_inc



Joined: Jun 09, 2009
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Location: Australia

PostPosted: Mon Jun 22, 2009 6:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah i see... thanks for that.

However I am unsure how much current the heater will draw. The data for CV4014 tubes states that heater current=0.3A. This seems massive...?
Do i just use this figure in my calculations?

Luke
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andrewF



Joined: Dec 29, 2006
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PostPosted: Tue Jun 23, 2009 3:51 am    Post subject: Reply with quote  Mark this post and the followings unread

0.3A is a typical current draw for a tube heater.

it is almost worth having a transformer just for this module.
Another option is a 6V or 5V wallwart, can usually find them in opshops for a dollar or 2.

My tube synth uses an old computer PSU to power the heaters, it was the cheapest (free) and easiest route.
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Thu Jun 25, 2009 5:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey guys.

Thanks a lot for clearing all that up. I will definitely have to rethink my power supply somewhat before i can plug up the tube VCA.......what a shame....

I will either have to up the current on my supply or think about incorporating another small transformer for the tube alone. If i did this, would i need a simple circuit to clean up the supply going to the heater??


thanks, Luke
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frequencycentral



Joined: May 25, 2008
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PostPosted: Tue Jun 30, 2009 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

A 7806 voltage regulator with a 100uf at the input and another at the output would be a simple way to get your 6 volts.
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hobgob_inc



Joined: Jun 09, 2009
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PostPosted: Tue Jun 30, 2009 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey freq central,

I did actually consider a Vreg but was not sure what other circuitry i may need. Are the 100uf's in series with the in/out or are they decoupling to ground??

I'm going to give this a go i think as my other modules don't seem to be drawing as much current as what i had anticipated.

Thanks for the tip,

Luke
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frequencycentral



Joined: May 25, 2008
Posts: 186
Location: UK

PostPosted: Tue Jun 30, 2009 5:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

hobgob_inc wrote:
Hey freq central,

I did actually consider a Vreg but was not sure what other circuitry i may need. Are the 100uf's in series with the in/out or are they decoupling to ground??

I'm going to give this a go i think as my other modules don't seem to be drawing as much current as what i had anticipated.

Thanks for the tip,

Luke


The 100uf's both go to ground, and provide a bit of decoupling. The advantage of a 7806 over a voltage drop resistor is that the 7806 will put out 6 volts however the supply voltage fluctuates, whereas the resistor method may fluctuate the divided voltage.

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hobgob_inc



Joined: Jun 09, 2009
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Location: Australia

PostPosted: Tue Jun 30, 2009 6:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Brilliant!!

thanks heaps for your input! I will let you know how it all goes.

Luke
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