Does anhone use those switching power supply for the heaters? - Page 2 - diyAudio
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Old 4th May 2007, 04:02 PM   #11
kevinkr is offline kevinkr  United States
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You'll definitely want to heat both sections of the 6C33 otherwise the tube behaves in a very non-linear manner for ac operation. Had this problem with my old otl design using this tube. (See my site for the sordid details.. )

Probably 12.6V operation will be easier to manage from a wiring gauge standpoint but high current 5V supplies are easier to come by. You might have to add an additional turn or two on the smps transformer to get proper operation at 6.3V - and usually you will also have to change a feedback resistor as well. Remote sense is a good choice in this application to eliminate the effects of voltage drop in the filament wiring.

There is a huge benefit to doing this however, and that is in terms of efficiency and weight. My filament transformers weighed about 18lbs apiece.
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Old 4th May 2007, 07:55 PM   #12
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Location: Alps:Tube amp designs over 150W, SMPS guru.
I regulary design using 10W smps for DC down-line front ends.. When using split load concertina or sim with high cathode voltage, I always lift (isolate) heater to roughly half cathode volts. i.e if cath =+100V use +50V and decouple with small 10uF electrolytic to ground. This will avoid heater/cathode noise esp if combination med mu triode and high gain pentode is used.
Additionally, common mode chokes may have to be fitted to both in/out to avoid noise in chassis. This is a common problem of charge-injection where a tab of a switching mos may be clamped to chassis via insulating washer.

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Old 4th May 2007, 08:51 PM   #13
gofar99 is offline gofar99  United States
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Greetings, In regard to Brian Beck's post. I have had similar experience using laptop supplies for tube preamps. I recently assembled a kit with various mods (on the diyaudioprojects.com site "Beauty") and found that it didn't sound quite right. On a scope (photo in the article) you could see the 70KHZ spikes that got through from the laptop smps. I used a pair of 100uh chokes and .1uf caps as filters. Other solutions would also work. On general principle I will now scope any smps to make sure high freq trash doesn't make it to the preamp, amp or whatever.

good listening,
gofar99
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Old 4th May 2007, 09:43 PM   #14
JoshK is offline JoshK  Canada
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Thanks for the tip Kevin! I haven't made up my mind yet on how to go about this. I did get my hands on some surplus iron, but as you said, they are huge and heavy. I'll probably use them to start with and consider a change to SWPS when it is running.
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