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

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Nick
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#1126 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Nick »

I just looked at the spec sheet for the 12A.

You can read all sorts of things on the internet.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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pre65
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#1127 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by pre65 »

Nick wrote: Sun May 17, 2020 12:35 pm I just looked at the spec sheet for the 12A.

You can read all sorts of things on the internet.
I have the RCA 112A data sheet, and yes there are all sorts of things on the internet, but not all can be believed.
Life is what happens to you while you're busy making other plans. John Lennon

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#1128 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Nick »

pre65 wrote: Sun May 17, 2020 12:50 pm I have the RCA 112A data sheet, and yes there are all sorts of things on the internet, but not all can be believed.
Exactly which is why I wondered why you posted
although I have read that slightly starving filaments may be an improvement.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#1129 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by pre65 »

Nick wrote: Sun May 17, 2020 3:32 pm
pre65 wrote: Sun May 17, 2020 12:50 pm I have the RCA 112A data sheet, and yes there are all sorts of things on the internet, but not all can be believed.
Exactly which is why I wondered why you posted
although I have read that slightly starving filaments may be an improvement.
But, by the same token, it does not mean it's untrue either.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
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#1130 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by pre65 »

pre65 wrote: Sun May 17, 2020 3:35 pm
Nick wrote: Sun May 17, 2020 3:32 pm
pre65 wrote: Sun May 17, 2020 12:50 pm I have the RCA 112A data sheet, and yes there are all sorts of things on the internet, but not all can be believed.
Exactly which is why I wondered why you posted
although I have read that slightly starving filaments may be an improvement.
But, by the same token, it does not mean it's untrue either.
I did a search on Audio-talk for "starved filaments" and there have been discussions about the topic. Whether the views held then are still applicable I can't say.
Life is what happens to you while you're busy making other plans. John Lennon

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#1131 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Andrew »

I have a new batch of PCB, Phil, if you want to 'speriment?
Analogue, the lost world that lies between 0 and 1.
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#1132 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by pre65 »

Andrew wrote: Sun May 17, 2020 8:39 pm
I have a new batch of PCB, Phil, if you want to 'speriment?
Can you remind me Andrew, do your boards have a trimmer for fine tuning the output ?
Life is what happens to you while you're busy making other plans. John Lennon

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#1133 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Andrew »

pre65 wrote: Sun May 17, 2020 8:58 pm
Andrew wrote: Sun May 17, 2020 8:39 pm
I have a new batch of PCB, Phil, if you want to 'speriment?
Can you remind me Andrew, do your boards have a trimmer for fine tuning the output ?
Yes, but I also keep saying trimmer pots are rubbish, and not to use them. Sadly, I am often ignored ;) However, if it's a prototype then I'll excuse you.
Analogue, the lost world that lies between 0 and 1.
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#1134 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Ray P »

Does anyone recall what the voltage drop across these DHT filament supplies is?

I'm planning to use a couple of these modules in my MoFo preamp - need them to deliver 9.3V @ 120mA so need to size a suitable transformer, which I guess will be >9VAC so I'll need to upgrade the filter caps too.
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#1135 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick »

Ray P wrote: Mon Dec 28, 2020 6:01 pm Does anyone recall what the voltage drop across these DHT filament supplies is?

I'm planning to use a couple of these modules in my MoFo preamp - need them to deliver 9.3V @ 120mA so need to size a suitable transformer, which I guess will be >9VAC so I'll need to upgrade the filter caps too.
About 4v I think (from the peak voltage obviously)

9v will get you about 8.7v max.
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#1136 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Nick »

I built one up for a 300b, for 5v out a few weeks ago, that needed 8.5v AC in before there was no dropping out on the scope on the low points of the input AC, 8.5v = 12v for no load, so that would put the drop at 7.5v, but that was with a 30va transformer feeding it.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#1137 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick »

Nick wrote: Mon Dec 28, 2020 6:18 pm I built one up for a 300b, for 5v out a few weeks ago, that needed 8.5v AC in before there was no dropping out on the scope on the low points of the input AC, 8.5v = 12v for no load, so that would put the drop at 7.5v, but that was with a 30va transformer feeding it.
Yes I fell into the trap of underestimating the VA requirements of the transformer. Immediate buzz killed when I got my head around the sizing and replaced them.
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#1138 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Ray P »

I've got a 10VAC transformer to hand but it looks as though I might need to go up to 12VAC - either way I'll need to go up to 25V rating on the filter caps.
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#1139 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by RhythMick »

Ray P wrote: Mon Dec 28, 2020 6:55 pm I've got a 10VAC transformer to hand but it looks as though I might need to go up to 12VAC - either way I'll need to go up to 25V rating on the filter caps.
What's the spec of the transformer?
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#1140 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Ray P »

RhythMick wrote: Mon Dec 28, 2020 7:00 pm What's the spec of the transformer?
I don't remember the specifics off hand - it's down in the garage - but it's relatively meaty for this requirement...
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