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Old 14th May 2011, 09:18 AM   #1
hihopes is offline hihopes  South Africa
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Default Best DHT heater?

Has anyone done reasonably thorough comparative testing of different DHT heater supplies? I am interested in Rod Coleman's boards, but wonder how they stack up against various others out there. I could build one myself, but doubt it would be as good as Rod's. I know Guido Tent is marketing one and I have seen one from DIY Hi-Fi Supply. I would like to get the best within reason, but price is important too. Any suggestions would be most welcome.
Thanks,
William.
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Old 14th May 2011, 01:20 PM   #2
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Don't forget choke input filament supplies!! Or some variation of that like small input caps round 220 - 470uF. I ignored that option because it seemed (and is) a huge undertaking in terms of weight and size. but when I tried it I immediately understood why others recommend it.

My preamp uses filament bias, and that demands a totally clean DC supply. So I actually ended up with a choke input supply feeding Rod Coleman boards.

There are a few such "hybrid" options - Rod uses a gyrator for example.

Andy
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Old 14th May 2011, 01:30 PM   #3
hihopes is offline hihopes  South Africa
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Thanks Andy. My feelings about choke input supplies are much like yours were. I would have to have a choke locally made, meaning I would have to provide a design and specifications for it and then hope they are followed properly. My first option is to look at a board; if that can be improved upon by filtering the supply to it, then I will do that too, but afterwards.
Do you know if anyone has done any comparisons between various boards?
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Old 14th May 2011, 01:42 PM   #4
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I've not compared boards but I have been through a few options. I used LM1084 supplies for a while and I still have one in my amp that needs replacing. There were the basis for the Ronan Reg which had two voltage regs followed by a current reg. They get the job done and are reasonably good. Advantage is the voltage is rock solid and not too sensitive to the input voltage.

Rod's supplies vary a little more with the input voltage but I don't think that matters, and they certainly run cooler which means smaller heatsinks so it's a win situation. They sound audibly better than LM1084 options.

I haven't tried Guido's options - he's done a lot of work on this.

I'm in the UK so Rod is kind of the home team for me, most helpful, and very easy and rewarding to communicate with - which is really useful when you're experimenting with these things. He really is very thorough and has tried out a large range of options to optimise his design.

Andy
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Old 14th May 2011, 04:59 PM   #5
Gluca is offline Gluca  Italy
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choke input + rod's regulator here, that is the best solution I found.
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Old 14th May 2011, 05:12 PM   #6
hihopes is offline hihopes  South Africa
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OK, that's 2 of you already. What sort of current are you guys working with and what value chokes are you using?

BTW I have already emailed Rod - waiting for his reply
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Old 14th May 2011, 07:37 PM   #7
Gluca is offline Gluca  Italy
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801A which draws 1.25A and 211 for 3.25A. I cannot remember choke's value but for 801A I am using a stock hammond (others are custom made), you can easily calculate min H and max A for the chokes.
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Old 14th May 2011, 08:50 PM   #8
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I use some big 280mH chokes I got NOS stock - 2.7A so pretty useful. First I used a 10Y with filament bias in my preamp, but eventually preferred the 26 in filament bias. Attached circuit.

I should really use choke input for all 3 stages of my setup - 26, 46 and 300b. One day when I can find space to put all the stuff! You need a rack just for the amp parts, what with HT PSU and filament supplies plus heatsinks etc.

Andy
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Old 14th May 2011, 11:04 PM   #9
Fuling is offline Fuling  Sweden
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LCLCL-filtered filament supplies works really well in my 6B4G SET. 25mH-22000uF-25mH-44000uF-112mH IIRC. Dead quiet but not "dead" sounding as might be the case when using voltage regulators.
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Old 15th May 2011, 07:00 PM   #10
hihopes is offline hihopes  South Africa
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MORE choke users! Looks like I gotta go that way - some time. I can wind small air-core chokes, up to a few mH. Wonder what will happen if I put some ferrite rods into the middles of them? Anyone tried it?
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