DHT Heater using VCCS - PCB or Kit (Possible Group buy)

cressy · Post by **cressy** » Sun Sep 07, 2014 1:26 pm

coming very late into this thread, i wondered if one of these modules would work with my nuvistor phono stage. needed is 2.1v at about 1.6a to heat all 4 of them. currently on there is a diy hifi supply module that really struggles to produce the low voltage and i think is dropping out of regulation as it is right at the bottom of its adjustment.

as the heater hum was the actual issue with it that caused it to be shelved one of these might fit the bill. ive just looked at a simple dc supply using psud but i dont think it will solve the problem and will still be too noisy.

looking at it, these modules can produce exactly what i want in terms of voltage and current, but i dont see anywhere where they have been used in a phono stage (unless i missed it, its a long thread.....)

cheers ant

pre65 · Post by **pre65** » Sun Sep 07, 2014 1:34 pm

Ant, could you try a higher voltage on the module and then use a resistor to drop it to the required value ?

cressy · Post by **cressy** » Sun Sep 07, 2014 1:38 pm

i considered doing that but was unsure as to how that would affect the board, it isnt mine so i didnt want to blow it up

IslandPink · Post by **IslandPink** » Sun Sep 07, 2014 2:12 pm

Are the nuvistors directly-heated or indirect ?
I'm assuming indirect, since you're asking about heating all four of them !
Either way, I'm pretty sure you can get the voltage you need - just a matter of changing the setting resistors .

cressy · Post by **cressy** » Sun Sep 07, 2014 2:17 pm

yep they are indirectly heated iirc there are 5 pins on them

IslandPink · Post by **IslandPink** » Sun Sep 07, 2014 3:59 pm

Then see :
http://www.audio-talk.co.uk/phpBB2/viewtopic.php?t=4050

pre65 · Post by **pre65** » Sun Sep 07, 2014 4:16 pm

At 1.6A a 1R would drop 1.6v.

I can't see how raising the module output by 1.6v (and avoiding regulator dropout ?) and reducing it again with a 1R could damage the module.

What transformer (or winding) is on the module input ?

IslandPink · Post by **IslandPink** » Fri Oct 24, 2014 3:24 pm

Unfortunately the magic smoke escaped from Andrew's latest minor iteration to the 3A board. No test on this one as yet.

Andrew · Post by **Andrew** » Fri Oct 24, 2014 3:57 pm

cressy wrote:yep they are indirectly heated iirc there are 5 pins on them

If they are indirect then one of the simpler modules could happily drive them as a series or parallel chain, cheaper too.

IslandPink · Post by **IslandPink** » Fri Nov 07, 2014 7:31 pm

IslandPink wrote:Unfortunately the magic smoke escaped from Andrew's latest minor iteration to the 3A board. No test on this one as yet.

My fault - minus 24V input to the circuit is not optimum !

To answer Ed's unanswered question from a few pages ago - yes, they are good for GM70 . If you use an SMPS, just feed about 24V into one of the initial cap placements .
At the moment, the only debate is whether you want C0G caps with or without conductive epoxy in the feedback loop to the current regulator.

Alex Kitic · Post by **Alex Kitic** » Sun Nov 09, 2014 9:16 am

IslandPink wrote: - yes, they are good for GM70...

Well, currently working on the RH70 (with GM70 tubes, obviously) I could not resist commenting...

The relentless grind of DIYers going towards DC for the filaments, and the various solutions to achieve DC heated filaments has almost had me drawn in the wrong direction. The internet is full of DC solutions for filaments: unregulated, choke first, choke after, voltage regulation, current regulation, servo... and of course, there is standard AC as an alternative, reasonably unusable for higher voltage filaments like the GM70 (20V makes for a lot of hum).

But I stopped and took a good look at what it takes - at lest 1.5x more AC power than necessary (more, actually, for the current regulation approach, due to the increased voltage drop) -- at high currents this becomes sort of an issue with heat as well, besides the inefficiency, consumption, size, etc. The size of the transformers, the heat emanating from the various parts of the DC circuitry, the need to engineer it all in such a manner as not to melt the box, or the other components, or my shelf...

Than I glance towards the other side of the bargaining table, where a small black box sits patiently waiting (electronic transformer for halogen light bulbs). Small, efficient, powerful, quiet...

"But haven't the good people adviced you against doing it? There is danger that you are going to hear artefacts..." - says the little guardian angel each of us has.

Yeah, right

My hearing must be seriously impaired, LOL... and with hearing it seems other stuff has gone as well (sanity, maybe?).

Well, what can I say but - enjoy DC and engineering unnecessary circuitry, while I enjoy music (with, as someone has put if very correctly "the blackest of backgrounds for direct heated tubes")!

pre65 · Post by **pre65** » Sun Nov 09, 2014 11:43 am

Alex, I think it's great that you find the modified halogen light modules so good.

I'd love to try them on my GK-71 but I fear the conversion work is beyond my skill level.

If you'd like to make a pair for me I would cover your costs, and postage.

Alex Kitic · Post by **Alex Kitic** » Sun Nov 09, 2014 2:57 pm

pre65 wrote: I'd love to try them on my GK-71 but I fear the conversion work is beyond my skill level.

If you'd like to make a pair for me I would cover your costs, and postage.

I really believe that's not something you couldn't do yourself - particularly having in mind that you are able to build amps.

The requirements are basically the same as for GM70, 20V 3A?

Since I am in this development process with the RH70, I guess it should be fairly easy to build a couple units more: I can always test it on the new breadboard to check how it works, and sounds... Would you need a stereo unit, or 2 mono units?

pre65 · Post by **pre65** » Sun Nov 09, 2014 3:18 pm

Yes, the filament voltage/current is the same as GM70.

My amps are monoblocks so I would need 2.

The amps are in the process of a power supply rebuild at the moment (dual mono) so it would be an ideal time to incorporate modified filament supplies.

Alex Kitic · Post by **Alex Kitic** » Sun Nov 09, 2014 7:11 pm

pre65 wrote: My amps are monoblocks so I would need 2.

The amps are in the process of a power supply rebuild at the moment (dual mono) so it would be an ideal time to incorporate modified filament supplies.

I have to check with the shop where I buy the units of the same type as the one shown in the RH813 blog entry. If you need 2, I have to get 2x 105VA units.

I understood your GK71 amps were monoblocks - but why do they have a dual-mono supply? Dual-mono usually means separate supplies in the same box? If you house your power supply in a separate box, maybe one transformer for both channels might be a better choice?

What is your usual mains voltage? The units I use are specified for 220V, but operating them at 240V should not be a problem (besides a slightly higher voltage that will also be reflected to the output). My home mains is 223-225V, and I use them also with my voltage boost transformer setup that elevates the mains voltage to a more usual 230-232V as in the continental EU.

You can send me an e-mail, or a PM for various details - I'll check out the shop this week to see whether they've got the right type of units.

audio-talk

DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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