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

[Nick]

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

You can read all sorts of things on the internet.

[pre65]

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.

[Nick]

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.

[pre65]

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.

[pre65]

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.

[Andrew]

I have a new batch of PCB, Phil, if you want to 'speriment?

[pre65]

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 ?

[Andrew]

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.

[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.

[RhythMick]

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.

[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.

[RhythMick]

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.

[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.

[RhythMick]

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?

[Ray P]

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...