DHT Heater using VCCS - PCB or Kit (Possible Group buy)
#1126 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
I just looked at the spec sheet for the 12A.
You can read all sorts of things on the internet.
You can read all sorts of things on the internet.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#1127 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
I have the RCA 112A data sheet, and yes there are all sorts of things on the internet, but not all can be believed.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#1128 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Exactly which is why I wondered why you posted
although I have read that slightly starving filaments may be an improvement.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- pre65
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#1129 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
But, by the same token, it does not mean it's untrue either.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
- pre65
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#1130 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#1131 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
I have a new batch of PCB, Phil, if you want to 'speriment?
Analogue, the lost world that lies between 0 and 1.
- pre65
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#1132 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
Can you remind me Andrew, do your boards have a trimmer for fine tuning the output ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#1133 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.
#1134 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.
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.
Sorry, I couldn't resist!
#1135 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
About 4v I think (from the peak voltage obviously)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.
9v will get you about 8.7v max.
#1136 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#1137 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.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.
#1138 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
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.
Sorry, I couldn't resist!
#1140 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)
I don't remember the specifics off hand - it's down in the garage - but it's relatively meaty for this requirement...
Sorry, I couldn't resist!