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Old 17th March 2014, 11:57 AM   #1
jervill is offline jervill  United Kingdom
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Default Voltage doubler and filament supply

Hi guys,

I have a 2v 1A valve that I want to light with DC. The filament transformer I have are the hammond 2.5v 3A. I've had a look at bridge rectifying direct but am unsure if there'll be enough smoothing or voltage left (allowing for mains variations). So, I'm looking at maybe using a bridge voltage doubler, CRC and zener to regulate voltage. Any caveats on using this configuration on a directly heated triode?

Thanks
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Old 17th March 2014, 01:45 PM   #2
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Hi,
use some of the old Ge-Diodes.

Hilmar
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Old 17th March 2014, 04:35 PM   #3
kevinkr is offline kevinkr  United States
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Take a look at Schottky rectifier diodes and chose the one with the lowest forward voltage (vf) that you can find at your load current. This might give you 800mV or more to play with, a low dcr choke of 5mH or so with some large electrolytics in a CLC configuration might get you there, look for ones with dcr (probably well <1 ohm) in the range required to drop the voltage to 2V at your nominal line voltage. Start by using a 2 ohm resistor as the load so you do not risk your tubes.
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Old 17th March 2014, 05:31 PM   #4
tinitus is offline tinitus  Europe
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I thought one point of using dc heater would be the reg to keep it stable
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Old 17th March 2014, 11:42 PM   #5
jervill is offline jervill  United Kingdom
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Thanks guys I'm looking at those options.


Quote:
Originally Posted by tinitus View Post
I thought one point of using dc heater would be the reg to keep it stable
I'm a beginner . Could you elaborate please the point you're getting at.
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Old 18th March 2014, 12:12 AM   #6
tomchr is offline tomchr  United States
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I see two options:

1) Unregulated DC supply like Kevinkr suggests. If you can find some diodes with a low enough forward voltage drop, you can probably make that work.
2) Use a different winding on the transformer so you can use an actual regulator on the filament supply.

Depending on your application, rectified DC may be good enough, though a regulated filament supply will always provide lower hum.

~Tom
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Old 18th March 2014, 12:36 AM   #7
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Jervill,

The value of a regulator is often more important to get rid of ripple than the regulating function. One has only to elevate the input to high enough above the output to make ripple disappear - can save more $ than a fat smoothing capacitor might.

Apology, late: Yes, Jervill, you may use a doubler, particularly to enable a regulating chip to be used.

Last edited by Johan Potgieter; 18th March 2014 at 01:03 AM.
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Old 18th March 2014, 01:42 AM   #8
jervill is offline jervill  United Kingdom
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Quote:
Originally Posted by Johan Potgieter View Post
Jervill,

The value of a regulator is often more important to get rid of ripple than the regulating function. One has only to elevate the input to high enough above the output to make ripple disappear - can save more $ than a fat smoothing capacitor might.

Apology, late: Yes, Jervill, you may use a doubler, particularly to enable a regulating chip to be used.
Yes, the drop through a regulating chip was the first impetus to look at a doubler after it was recommended that I use one. But, I've not used any such chips before so I need to read up on it.

I'm trying to use a 102d (DHT) as an input tube so it is an important consideration how much noise there will be at this stage. I've only used DC on indirectly heated triodes (6sl7, 76, 6sn7...) and that was unregulated in my phono pre. Quiet enough, but I'm not sure what then is optimum on DHTs. As Tom mentions, it may be good enough. Just in case it's not I want to consider all options.

Last edited by jervill; 18th March 2014 at 01:51 AM.
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