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dc to dc stepdown convertors for dh filliments?

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Posted on April 26, 2015 at 11:13:47
amnesiac
Audiophile

Posts: 717
Joined: August 21, 2002
 I have bought some dc to dc converters off ebay. It says in one page they have to be isolated from ground.

Does this mean they go boom when the cathode is grounded?

I tried to search for an isolated version but only small insulated versions come up.

I though I had found a very easy and efficient way of stepping down higher voltage supply's to the low voltage filaments.

They are mass produced to power leds and charge battery's I think.

'

 

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RE: dc to dc stepdown convertors for dh filliments?, posted on April 26, 2015 at 11:22:47
drsx
Audiophile

Posts: 369
Location: around
Joined: September 11, 2005
 I don't see where it says anything about isolation. Just notice that the input and output ground are connected, so you'll need a separate winding + rectifier for each filament supply, and that the input supply should be floated.

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 26, 2015 at 12:35:47
amnesiac
Audiophile

Posts: 717
Joined: August 21, 2002
 No not on this page on another page. I just included that page to show the sort of converter I want to use. Here is the page.

I have actually built a quad module and tested it into 4 resisters and it works beautifully but I am yet to try it in a amp after reading this note I am worried! In theory if it worked it should be a very versatile little module capable of powering many different dh filaments. Well that was my plan anyway.

I had plans for larger tubes too. Power supplies can be built and choked at higher voltages than stepped down to the lower more difficult voltages. Rectifying and filtering low voltages is much less efficient then say at 20 volts then stepping down to 2 to 5 volts with only 5% loss.

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 26, 2015 at 12:58:03
drsx
Audiophile

Posts: 369
Location: around
Joined: September 11, 2005
 The item in the link is not even remotely the same thing. The first one does not have isolated grounds from in to out, and thus must use an individual floating supply for each filament. Think of it as a standard voltage regulator.

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 26, 2015 at 21:09:27
amnesiac
Audiophile

Posts: 717
Joined: August 21, 2002
 I am thinking I should just try it on my 10y amp which uses a conventional choked supply . I will know if it doesn't sound as good that way.I have searched ebay for the actual boards I used they don't seem to be too easy to find.The boards do have a isolated ground on the board physically anyway.

I was liking the digital read out on the one shown for ease of set up experimenting with output voltages which is worth playing with tt filimants. I am worried failure mode for these will be input voltage on my filimants.

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 27, 2015 at 07:11:05
Al Noakes
 The only digital readout you need is a lit filament and the only 'failure' mode will probably be a worse sounding amplifier . Avoid putting junk in your equipment , you'll stay happy this way :)

Al

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 29, 2015 at 23:34:05
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 @Al Noakes
I usually do not support what dealers say, but in this case I must.
A very good way of putting it - "worse sounding amplifier" "junk".

Particularly when the OP doesn't seem to know what exactly he is/should be doing.

That said, I am trying to advocate the HF approach using relatively cheap parts (electronic transformers for halogen light bulbs, modded, of course).

******

http://rh-amps.blogspot.com/

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 30, 2015 at 10:35:57
Al Noakes
 'That said, I am trying to advocate the HF approach using relatively cheap parts (electronic transformers for halogen light bulbs, modded, of course).'

If I think it's worth it , I tend to throw a bit of money at it . Nothing like the sort of money people pay for silly capacitors but more than a chunk of Chinese junk . These cheap Ebay items make people lazy , I'm sure applications can be found within amplifiers for these cheap boards but I certainly would be very apprehensive using these things on a directly heated valve's filament . I don't know about you but I find the filament supply is one of the most critical aspects of an amplifier . I have never used a halogen supply but eventually may have to use these to keep the size/weight of the intended amplifier down . VT127A have 5V 10.5A filaments , I have the transformers/chokes but the filament supply alone would weigh 25kgs per channel . This is why I'd consider a halogen supply here . It's nice to get optimum sound but sometimes nicer to have an amplifier that can be moved :)

Al

 

RE: dc to dc stepdown convertors for dh filliments?, posted on April 30, 2015 at 16:36:42
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 VT127A have 5V 10.5A filaments , I have the transformers/chokes but the filament supply alone would weigh 25kgs per channel . This is why I'd consider a halogen supply here . It's nice to get optimum sound but sometimes nicer to have an amplifier that can be moved :)

Exactly my two points:
1) definitely can be moved: just look at the size of the filament supply that I ended up using on my RH813, getting 2 secondaries 10V 5A each as well as one 6.3V 1A secondary for the driver tubes;
2) black background, cleaner than DC - with very clean sound, it's AC after all, but without the hum, and sounds a bit cleaner than mains AC (which might be an effect of the totally black background compared with some mains hum from ordinary AC).

It's definitely worth the effort, but not really as cheap as it looks because the parts needed for the mod eventually cost just as much as the electronic transformer itself.

******

http://rh-amps.blogspot.com/

 

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